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The New Leader in ADA Compliant Detectable Warnings |
ACCESS BOARD RESEARCH
Detectable Warnings: Synthesis of U.S. and International Practice
PDF version
12 May 2000
prepared by:
Billie Louise Bentzen, Ph.D.
Janet M. Barlow, COMS
Lee S. Tabor, architect
Accessible Design for the Blind
P.O. Box 1212
Berlin, Massachusetts 01503 USA
978-838-2307 voice / fax
bbentzen@ma.ultranet.com
The products shown in this report are only intended to serve as
illustrated examples and are not intended as endorsements of the
products. Other products may be available. The Access Board does not
evaluate or certify products for compliance with its accessibility
guidelines. Users are advised to obtain and review product
specifications for compliance with the accessibility guidelines.
ACKNOWLEDGEMENTS
The authors wish to express their appreciation to all who generously contributed their time and efforts in providing information, specifications, and photographs, to those who participated in interviews, and to those who gave permission for us to list their names in this publication as contacts for more information.
The authors are thankful to Lois Thibault of the U.S. Access Board for the provision of difficult to obtain resources, and for her careful editing and suggestions on content organization.
We also wish to acknowledge the dedicated research assistance of Abigail Tabor and Rebekah Barlow.
ILLUSTRATION CREDITS
All drawings by Lee Tabor except as noted.
All photos by the authors except as noted.
Photos by Martin Miller: cover, 8-15 through 8-30.
Photos by Lois Thibault: 1-3, 1-4, 2-5, 3-7, 4-4, 4-13, 5-1, 5-2, 5-3,
5-5, 5-11.
Photos by Murray Mountain: 3-5, 4-6, 4-13, 4-14.
Photos by Douglas Barlow: 2-4, 3-6, 5-8.
Photos by Lukas Franck: 5-6, 5-14.
Photos by Ken Zimmerman: 5-7, 6-2.
Photo by Barry Eager: 3-1.
Photo by Robert Laurie: 5-4.
Photos courtesy of Beneficial Designs: 4-5, 4-7.
Photo courtesy of Rick McCarter: 5-10.
Photo courtesy of Maryvonne Dejeammes: 4-10
Photos reproduced, with permission, from K&omul;nig, 1996: unnumbered,
p. 64, 4-11, 4-12.
Photo reprinted from Ketola & Chia, 1994: 3-3
Drawing by Joanne Bergen reproduced from Bentzen et al., 1994: 2-6.
Drawing reproduced, with permission, from Guidance on the use of tactile
paving surfaces, 1998: 3-4.
Drawings reproduced, with permission, from &Omul;NORM V 2102: 4-1, 4-2.
Drawing reproduced, with modification, by permission, from Sawai et al.,
1998: 4-3.
Photos and drawings from manufacturer’s brochures: Engineered Plastics, 1-7; Disability Devices: 1-8; Architectural Tile & Granite: unnumbered, p. 26; Summitville, 5-12; Carsonite; 5-15; Strongwall Industries: 7-8, 7-9; Increte: 7-10; Cote-L: 7-11, 7-13, 7-14; Vanguard ADA Products: 7-12.
CONTENTS -- DETECTABLE WARNINGS: SYNTHESIS OF US AND INTERNATIONAL PRACTICE
[Page numbers listed below refer to page locations in the hardcopy text version of the document.]
Content of synthesis / 9
Purpose of synthesis / 9
Sources of information / 9
How people who are blind detect streets
Curbs are a definitive cue / 11
How curbs are detected / 11
Elimination of curbs / 11
The need to rely on multiple clues / 11
The difficulty of finding and using multiple clues / 12
Detecting transit platform edges
Techniques for detecting transit platform edges having a drop-off / 12
Blind people at risk at transit platform edges / 12
Japan / 13
United Kingdom / 13
U.S. research to identify detectable warning surfaces
Extensive research program on detectability / 13
Importance of under foot detectability / 14
Early projects / 14
Surfaces for transit platforms / 14
ANSI A117.1-1980- Tactile warnings / 15
Specification of texture / 15
ANSI A117.1-1986- Detectable warnings / 15
Implementation of ANSI A117.1-1980 & 1986 / 15
ADAAG (1991)- Truncated dome detectable warnings / 16
Controversy in the U.S. / 16
ANSI A117.1-1992- Deleted detectable warning specifications / 16
Some ADAAG requirements for detectable warnings suspended / 16
Research on detectable warnings recommended / 17
Rights-of-way guidelines / 17
Local and state guidelines / 17
Variety of recommendations / 17
ICC/ANSI A117.1-1998- Equivalent detectability / 18
Other textured walking surfaces
Other surfaces / 18
Raised design flooring / 18
Directional tactile paving / 18
Truncated dome detectable warnings
Focus on truncated dome detectable warnings / 19
Chapter 2. Detectable Warnings in ADAAG
Definition of detectable warnings / 21
Specification for detectable warnings / 21
Visual contrast / 21
Geometry of detectable warnings
Dome alignment & pattern / 21
Dome profile / 22
Detectable warnings at transit platform edges
Requirement for transit platform edges (ADAAG 1991) / 22
Why the warning is placed at the platform edge / 22
Why the warning is 24 inches wide / 22
Width & placement decision also based on positive experience / 23
Detectable warnings at curb-ramps, hazardous vehicular ways & reflecting pools
Requirement at curb-ramps / 23
Requirement at hazardous vehicular ways / 23
Requirement at reflecting pools / 24
Chapter 3. Recent Research on Detectable Warnings
Effect of curb-ramps on blind pedestrians
Effect on street detection / 26
Effects of slope and placement / 26
Effects of detectable warnings on travel by blind pedestrians
Detectable warnings are helpful at curb-ramps / 26
Detectable warnings reduce falls at transit platform edges / 27
Effects of detectable warnings on people with mobility impairments
Effects on transit platforms / 27
Effects at slopes or curb-ramps / 27
Benefits at curb-ramps / 27
Effects at hazardous vehicular ways / 28
Evaluation of detectable warning materials
Laboratory testing / 28
Field testing / 28
Research on sound on cane-contact differences
A test of difference in sound / 29
Contrast of detectable warnings / 29
Research shows value of safety yellow / 29
Standards for safety yellow / 29
Many truncated dome surfaces / 30
Many truncated dome surfaces found to be highly detectable / 30
Factors which have little effect on detectability / 30
Factor which decreases detectability / 30
Research on dome dimensions & spacing
Japanese research / 30
Dome height tests / 31
Dome diameter and spacing tests / 31
Optimal dome diameter & spacing combinations / 31
Illustrations of international tactile ground surface indicators
Chapter 4. International Use of Warning Surfaces
Tactile ground surface indicators / 34
TGSIs as a wayfinding system / 34
TGSIs to indicate a variety of features / 34
TGSIs for warnings & directional information / 34
U.S. approach to warning surfaces / 34
U.S. approach to directional surfaces / 35
Usage by country
Japan / 35
United Kingdom / 36
Australia / 39
New Zealand / 41
Italy / 42
France / 44
Germany / 45
Austria / 46
Netherlands / 48
International Organization for Standardization (ISO) / 49
Technical Committee 173 (ISO/TC173) / 49
ISO draft on TGSIs / 49
Applications / 49
Installation of warning surfaces / 50
Chapter 5. U.S. Use of Detectable Warning Surfaces: Case Studies
Locating U.S. installations of detectable warning surfaces
Developing a list of locations / 52
Mail survey / 52
Other information sources / 52
Responses to survey / 52
State & local requirements / 52
Interviews regarding detectable warning installations
Interview / 53
Locating appropriate persons / 53
Types of locations for detectable warnings / 53
City interviews / 53
Transit system interviews / 54
Other interviews / 54
Interview questions / 55
Snow removal / 55
Materials / 55
Color of detectable warnings / 56
Installation dates / 56
Installation costs / 56
Installation method / 56
Interview results - installation problems
Installation problems or difficulties / 56
Interview results - maintenance
General maintenance / 57
Snow & ice removal / 57
Interview results - durability
Durability / 57
Interview results - public reaction
Public reaction, problems or concerns / 58
No record of any lawsuits / 59
Lawsuits, but no details / 59
Case studies
Austin, Texas / 59
Metropolitan Atlanta Rapid Transit Authority (MARTA) / 61
Roseville, California / 62
Metro North Railroad / 63
Harrisburg, Pennsylvania / 65
Massachusetts Bay Transportation Authority (MBTA) / 66
Cleveland, Ohio / 67
Baltimore County, Maryland / 68
Bay Area Rapid Transit (BART) / 69
Claremont, California / 70
Chapter 6. U.S. Use of Detectable Warning Surfaces: Applications
Purpose of this chapter / 73
ADAAG / 73
California Title 24 / 73
Project ACTION panel of experts / 73
Accessible Rights-of-Way: A Design Guide / 74
Designing Sidewalks & Trails for Access: Part II. A Best Practices Guidebook / 74
ACB Street Design Guidelines / 74
Roseville, CA / 74
Cambridge, MA / 74
Austin, TX / 74
Towson, MD / 74
AER resolutions / 74
ACB resolutions / 75
NFB resolutions / 75
Recommendations for detectable warnings at curb-ramps
Whole surface of ramp - ADAAG / 75
Whole surface of ramp - California Title 24 / 75
Bottom 3 feet - Roseville, CA / 76
Bottom 2 feet - Multiple sources / 76
Parallel curb ramp / 76
Detectable warnings at hazardous vehicular ways
California Title 24 / 76
Detectable warnings at medians & islands
Cut-through medians / 77
Cut-through splitter islands / 77
Detectable warnings at raised crosswalks & intersections
Raised crosswalks & raised intersections / 78
Fitting to a blended curb at a raised intersection / 78
Chapter 7. U.S. Detectable Warning Products
Manufacturing standards / 80
ADAAG technical specification / 80
Brick pavers / 80
Pattern repetition / 80
Complementary tile pairs / 81
Working with irregular shapes / 81
Truncated dome diameter / 81
Manufacturers’ response / 81
Types of detectable warning products
Summary / 82
Use of term "detectable warning" / 82
Rely on current specifications / 82
Details should be verified / 82
Definition / 82
Natural stone, stone composites, & ceramic tile / 83
Brick pavers / 83
Large precast units / 83
Definition / 83
Rigid and flexible composition / 83
Tile size / 84
Installation / 84
On-site fabrication of truncated dome surfaces
Definition / 84
On-site production of domed surface / 84
Stamped concrete / 84
Detectable warnings that are not on grade / 85
Surface-applied dome products / 85
Characteristics of detectable warning products
Slip resistance / 86
Color / 86
Contrast / 86
Sound on cane-contact & resiliency / 86
Durability / 87
Detectable warning product matrix
Matrix / 87
Photographs of detectable warning products
Sample photography / 88
16 photographs of product samples / 89
Detectable warning manufacturers
List of manufacturer names and contact information / 90
References and Annotated Bibliography / 96
Glossary / 107
Questionnaire for interviews regarding detectable warning installations / 109
Content of synthesis
This synthesis summarizes the state-of-the-art regarding the design, installation and effectiveness of detectable warning surfaces used in the U.S. and abroad. The need for a warning surface is documented. U.S. and international research on detectable warnings is reviewed. U.S. and international standards and guidelines for detectable warnings are presented. Use of detectable warnings in the U.S. and abroad is described, with illustrative case studies. Information is provided on U.S. detectable warning products and manufacturers. Jurisdictional recommendations for the use of truncated dome detectable warnings are summarized and illustrated.
Purpose of synthesis
The synthesis was developed under contract to the U.S. Access Board. It will be helpful to transportation engineers, planners, and other interested persons working to make public rights-of-way more accessible to people who have visual impairments.
Sources of information
Information about detectable warning products and installations comes from these sources. Information from the U.S. is based on input from individuals representing public and private agencies or businesses that have installed truncated dome detectable warnings. International information is based on input from individuals who are familiar with the development and regulatory history of warning surfaces in each country. Information on detectable warning products is based on interviews with company representatives and on company literature.
Fig. 0-2. Curb ramp complying with ADAAG 4.7.7 (temporarily suspended), Cleveland, OH. Photo shows a perpendicular curb ramp surfaced with brick truncated dome pavers on the whole surface of the ramp, excluding the flares.
BACKGROUND
Summary
This chapter includes information on travel clues and cues used by persons with visual impairments at curb-ramps and transit platform edges. Early approaches to providing additional cues in Japan and the United Kingdom are described. The results of U.S. programs of research to identify detectable warning surfaces are summarized, and U.S. standards are discussed.
Chapter contents
This chapter covers the following topics.
How people who are blind detect streets / 11
Detecting transit platform edges / 12
Early solutions / 13
U.S. research to identify detectable warning surfaces / 13
History of U.S. standards / 14
Other textured walking surfaces / 15
Truncated dome detectable warnings / 16
HOW PEOPLE WHO ARE BLIND DETECT STREETS
Curbs are a definitive cue
The development of sidewalks and streets, with their identifying curbs—the network of vehicular and pedestrian circulation—gave pedestrians who were blind predictable environmental features that could be used to maintain orientation and safety when traveling independently. Curbs designed to separate pedestrian from vehicular flow and to provide a gutter edge to contain and direct water flow, provided a reliable cue to pedestrians who were blind that they had arrived at an intersecting street. Detection of a down curb unmistakably informed blind pedestrians that they had come to the end of the sidewalk and that their next step would be into the street.
How curbs are detected
Detection techniques depend on the travel aids used by people who are blind, such as long canes or dog guides, and their amount of vision. People who are blind and use a long cane for a travel aid detect a curb, or any other drop-off such as stairs or a platform edge, by a change in the angle of the wrist and the failure of the cane to contact the sidewalk at the expected level. People who use dog guides are alerted to the presence of a curb or other drop-off when their dogs stop. They then confirm the presence of the drop-off with a foot. People who have low vision, and do not use either a long cane or dog guide, rely on differences in color or shading of the walking surface. The sidewalk and street may have visual contrast, or the curb material may contrast with the sidewalk or street.
There are a number of other sources of information about the location of the curb indicating the end of the sidewalk (and the beginning of the street) which may be used by any person having a visual impairment, regardless of their travel aid or amount of low vision. These include traffic sounds, the slope of the sidewalk, the end of a building line, and changes in sun or wind. These are all simply clues to the sidewalk/street boundary. None is a definitive cue.
Elimination of curbs
Accessibility requirements that were developed in the 1960s resulted in the disappearance of curbs at many intersections. Curb-ramps, blended curbs and depressed corners became common features. Recently, raised crosswalks and intersections have been introduced from Europe. Hotel, retail, airport, and other building entrances have been designed without a curb separating them from street grade, for easy access for pedestrians using wheeled luggage or carts, as well as for persons with disabilities.
The need to rely on multiple clues
In the absence of a definitive cue—the curbed sidewalk—at the sidewalk/street boundary, it has become much more difficult for pedestrians who are blind to detect streets. When blind pedestrians do not detect a curb at the end of a block, they must rely on multiple clues which, taken together, indicate the high probability that they have come to a street. They may detect a change in slope, which could be a curb ramp, a change in terrain, or a broken sidewalk. The end of a building line or grass line may suggest that there is a street directly ahead. Changes in sun and wind are also clues. However, none of these clues, by itself, confirms the presence of an intersecting street. One of the most reliable clues, when it is present, is the sound of traffic on the intersecting street. But in many locations, and at different times of the day or days of the week, there may be little or no traffic.
The difficulty of finding and using clues
Complex traffic operations, including actuated signals and right turn on red, have made it increasingly difficult to analyze the environment using vehicular sound. Large traffic volume and high ambient sound often mask traffic flow and the sounds of vehicles starting and stopping. Blind pedestrians have become increasingly at risk in urban environments where traffic flow information is complex, unclear, masked by other sounds, or absent. The trend toward aggressive driving has decreased the likelihood that drivers will stop for pedestrians in crosswalks at unsignalized intersections, and the general decline in pedestrian traffic has made it increasingly difficult for blind travelers to obtain assistance for street crossings where needed.
DETECTING TRANSIT PLATFORM EDGES
Techniques for detecting transit platform edges having a drop-off
Detection techniques depend on the travel aids used by people who are blind, and their amount of vision. People who are blind and use a long cane for a travel aid detect the edge of a transit platform having a drop-off by a change in the angle of the wrist and the failure of the cane to contact the platform at the expected level. They must normally come to a stop after taking no more than one step following the cane information.
People who use dog guides are alerted to the presence of the platform edge when their dogs stop. They then confirm the exact location of the platform edge drop-off with a foot. People who have low vision, and do not use either a long cane or dog guide, rely on differences in color or shading between the platform and the track bed. Usually the platform is a lighter color than the track bed, although the reverse may also be true. Sometimes people having low vision are able to see a colored safety line defining the end of the safe waiting area, and sometimes illumination patterns may be helpful in determining the location of the platform edge.
There are a number of other sources of information about the general location of the platform edge, such as other riders waiting a safe distance from the drop-off, and changes in air currents.
Blind people at risk at transit platform edges
Falling and fear of falling at high-level transit platform edges have been found to be a major problem and cause of anxiety in blind transit riders (Bentzen, Jackson & Peck, 1981). In Bay Area Rapid Transit (BART) in San Francisco, during the ten years before the installation of detectable warnings along platform edges, approximately one fourth of all accidents along the edges of raised platforms involved persons who were visually impaired (McGean, 1991).
Japan
Japan was the first country to make up for the information lost by removal of curbs at intersections. Beginning in the 1960s the Japanese installed a warning surface on curb-ramps that was detectable both underfoot and by use of the long cane. Warning surfaces at curb-ramps and blended curbs are now commonplace throughout Japan. Warning surfaces are also used on nearly all high-level transit platforms.
Surface texture
Most of the early Japanese surfaces intended to be warnings had a surface configuration of domes about 5 mm high, which might be somewhat flattened or truncated on top, arranged in a square pattern, and having domes about 65 mm apart on center.
Placement, size, and material
Warning surfaces typically were placed on the lower end of curb-ramps, or along the former curb line where there were blended curbs. Warning widths varied from about 30 mm to about 900 mm. Materials used included rubber, stainless steel, cast pavers, and tiles. On transit platforms, warning surfaces were commonly 300 mm wide and placed about 900 mm back from platform edges. Warning surfaces were used in conjunction with directional surfaces to form networks of travel paths for persons who are visually impaired.
Fig 1-1. Japanese transit platform showing detectable warning at the top of stairs and parallel to the platform edge, and a tactile path leading from the stairs to the waiting area along the platform. Photo shows detectable warnings at top of stairs, a linear tactile path going toward the platform edge, a junction of paths at a right angle, and a one foot deep tactile path along the platform at about three feet from the platform edge.
United Kingdom
In the United Kingdom, a warning surface having a standardized pattern of truncated domes, referred to as modified blister paving, has been recommended for use in specified locations and dimensions since 1983 (Department of Transport, 1991; Gallon, Oxley & Simms, 1991; Textured pavements to help blind pedestrians, 1983).These warnings can now be found throughout the United Kingdom on curb-ramps and blended curbs. Most are cast pavers.
U.S. RESEARCH TO IDENTIFY DETECTABLE WARNING SURFACES
Extensive research program on detectability
An extensive program of research in the United States to identify walking surfaces that could be used to alert people with visual impairments to the presence of hazards such as streets and platform edges began in 1980. This research has been conducted by a number of researchers and sponsored by the Federal Highway Administration, the Urban Mass Transportation Administration (now known as the Federal Transit Administration), the Federal Transit Administration, and the U.S. Architectural and Transportation Barriers Compliance Board (Access Board).
Importance of under foot detectability
Many tested surfaces have been found to be non-detectable or minimally detectable; these are not appropriately considered to be detectable warnings. It is essential that warnings be highly detectable under foot as well as by use of the long cane. A minority of people who are legally blind regularly use a long cane for obtaining surface information as they travel. Other people who are visually impaired use dog guides or their low vision. To detect changes in walking surfaces, they rely on visual contrast and/or under foot information. Low vision is quite variable; a person who often can see streets, platform edges and stairs may sometimes be unable to see them because of glare, poor illumination, poor visual contrast, or fatigue. Many surfaces that seem likely to be highly detectable are only somewhat detectable, especially under foot. Figure 1-2 shows a number of surfaces that have been found to be minimally detectable.
Fig. 1-2. Cross-sections of surfaces found to be low in detectability. Drawn at full scale. Drawing shows profiles of eight grooved surfaces. Grooves vary in width between ¼" and 2", in depth between 1/16" and ¼", and in spacing between ¼" and 2".
Early projects
The earliest projects in the U.S. emphasized detection by blind persons who were using a long cane, of a warning surface adjoining brushed concrete. A ribbed rubber mat was found highly detectable to blind persons using a long cane because it varied from concrete in texture, resiliency and sound (Aiello & Steinfeld, 1980). A resilient tennis court surface was found to be highly detectable to blind long cane users (Templer & Wineman, 1980). Various steel surfaces were found to be highly detectable on the basis of differences in sound between steel and concrete when contacted by a long cane used in a tapping technique (Templer, Wineman & Zimring, 1982).
Surfaces for transit platforms
A warning surface was needed for use on transit platforms, which was highly detectable when it adjoined a variety of surfaces in common use on platforms. The next series of projects addressed this need, and identified two surfaces suitable for transit platform use, which were both highly detectable when used in association with brushed concrete, exposed aggregate concrete, rubber (Pirelli) tile, and heavy wooden decking (Peck & Bentzen, 1987).
One was a prototype "corduroy" surface having raised ribs which were dome-shaped in cross section, 3/16 in high, ¾ in wide, and 2 in apart on center. The other was a resilient rubber tile having a truncated dome pattern (the pattern that was the basis for the technical specification in the Americans with Disabilities Act Accessibility Guidelines (ADAAG).
Both of these surfaces were more highly detectable in a noisy environment than a rough textured steel surface or a resilient tennis court surface. Both of these surfaces were highly detectable to blind persons both under foot and with the use of a long cane. The truncated dome surface was recommended for a standard warning surface because similar surfaces were being used for warnings in Japan and England. Linear surfaces were being used in Japan as directional surfaces.
ANSI A117.1-1980—Tactile warnings
In the 1980 ANSI (American National Standards Institute) Standard, A117.1-1980 American National Standard: Specifications for Making Buildings and Facilities Accessible to and Usable by Physically Handicapped People, what were then referred to as tactile warnings were specified for the entire walking surface of curb-ramps. A 36 in (915 mm) wide strip was specified along the full edge of blended curbs, and a tactile warning surface was also specified for tops of stair runs except those in dwelling units, in enclosed stair towers, or to the side of the path of travel. Further, tactile warnings were specified for edges of reflecting pools that did not have railings, walls or curbs.
Tactile warnings were to be standardized within a building, facility, site, or complex of buildings
ANSI standards are voluntary consensus standards. ANSI A117.1-1980 includes specifications for curb-ramps as well as tactile warnings.
Specification of texture
ANSI A117.1-1980 4.29.2 "Tactile Warnings on Walking Surfaces. Tactile warning textures on walking surfaces shall consist of exposed aggregate concrete, rubber, or plastic cushioned surfaces, raised strips, or grooves. Textures shall contrast with that of the surrounding surface…. Grooves may be used indoors only."
ANSI A117.1-1986—Detectable warnings
ANSI A117.1-1986 American National Standard for Buildings and Facilities—Providing Accessibility and Usability for Physically Handicapped People, continued to specify the same warning textures, by then called detectable warnings, on the full width and depth of curb-ramps, at uncurbed intersections, at tops of stair runs, and at reflecting pools.
Implementation of ANSI A117.1-1980 & 1986
Early implementations of the ANSI A117.1-1980 and ANSI A117.1-1986 standard for tactile warnings included a number of surface treatments such as grooved concrete, which were subsequently found not to be highly detectable to pedestrians who are blind. Grooved concrete is still used in some jurisdictions today, and it is sometimes called a detectable warning although it has not been found to be highly detectable and has not been recommended in any U.S. standard for outdoor use. The photos below illustrate a variety of curb ramp treatments that are not now considered to be detectable warnings because they have not been found to be highly detectable and are not standardized, or because they are easily mistaken for other common features in the pedestrian environment.
Fig. 1-3. A blended curb in Columbus, OH, which uses difficult-to-detect rows of raised brick. Photo on left shows a wide radius blended curb with rows of bricks set in edgewise separated by horizontal bricks to act as a warning. Photo on right is a close-up of the previous photo. Each row of bricks set edgewise, end to end, in rows parallel to the curb line, is separated by one row of bricks laid flat, end to end. The edgewise bricks appear to be about ¼" above the level of the horizontal bricks.
Fig. 1-4. (Left) Curb ramp with a minimally detectable grooved surface in Phoenix. Photo shows a 4’ wide curb ramp with narrow grooves parallel to the direction of travel.
Fig. 1-5 (Right) A curb ramp with a narrow border of detectable warning pavers at the sides and smooth pavers in the middle. Blind pedestrians could easily miss the narrow border of detectable warning pavers. Photo shows a blended curb at a corner, having a very elaborate treatment on a cement sidewalk, of a single row of gray bricks with domes, filled with small, gray, flat pavers.
ADAAG (1991)—Truncated dome detectable warnings
In 1991, the Architectural and Transportation Barriers Compliance Board (Access Board) published the Americans with Disabilities Act Accessibility Guidelines (ADAAG), which included scoping and technical specifications for truncated dome detectable warnings at curb-ramps, hazardous vehicular ways, reflecting pools, and edges of transit platforms having drop-offs. The ADAAG specifications are provided in Chapter 2. The specifications were based on the extensive program of research described above.
Controversy in the U.S.
Both specifications and scoping for detectable warnings quickly became one of the most controversial issues in ADAAG. Truncated dome detectable warnings were strongly advocated by some individuals and organizations of blind travelers and the orientation and mobility profession. They were strongly opposed by other individuals and organizations of blind travelers and by some individuals and organizations representing people concerned with safety of persons with mobility impairments. Blind persons opposing detectable warnings at intersections and hazardous vehicular ways claimed that other cues were available and that detectable warnings were an unnecessary and costly feature.
Additionally, concerns were expressed regarding the use of truncated dome detectable warnings on sloped curb-ramps and the possibility of trips and falls for sighted pedestrians, particularly women wearing high heels, as well as difficulty for wheelchair users in traversing ramps with additional "bumps."
CABO/ANSI A117.1-1992—Deleted detectable warning specifications
By 1992, some members of the ANSI A117.1 committee were no longer certain that detectable warnings were needed in any location, and all specifications for the texture and for its use in various locations were dropped. There remained only the mention of standardization within a building, facility, site, or complex of buildings.
Some ADAAG requirements for detectable warnings suspended
Since April 1994, ADAAG requirements for truncated dome detectable warnings at curb-ramps, hazardous vehicular ways and reflecting pools have been temporarily suspended while the Access Board has sought additional research on whether detectable warnings are needed at curb-ramps and hazardous vehicular ways, whether detectable warnings help people with visual impairments, and whether detectable warnings have adverse impacts on people with mobility impairments. The requirement for truncated dome detectable warnings at transit platform edges remains in effect.
Research on detectable warnings recommended
The requirement for detectable warnings at curb-ramps, hazardous vehicular ways, and reflecting pools was suspended pending research to determine whether curb-ramps resulted in problems for pedestrians who are blind, whether detectable warning surfaces helped blind pedestrians, and whether detectable warnings on curb-ramps had adverse impacts on persons with mobility impairments. See Chapter 3 for a summary of this research.
Rights-of-way guidelines
In 1994 the Access Board proposed rights-of-way guidelines, Section 14, adapting the basic ADAAG 1-10 provisions for application to public rights-of-way. However, Section 14 was not adopted as part of the Department of Justice Standard for Accessible Design. Accessible Rights of Way: A Design Guide published by the Access Board in 1999, states: "Although no Federal scoping or technical requirements have been established that apply specifically to public rights-of-way, both ADAAG and UFAS [Uniform Federal Accessibility Standards] contain technical requirements for the construction of accessible exterior pedestrian routes that may be applied to the construction of public rights-of-way. In the absence of a specific Federal standard, public entities may also satisfy their obligation by complying with any applicable State or local law that establishes accessibility requirements for public rights-of-way that are equivalent to the level of access that would be achieved by complying with ADAAG or UFAS."
Local and state guidelines
Many state and local government agencies have adopted standards that include specific recommendations intended to meet pedestrian accessibility requirements. The following pedestrian guidelines were reviewed to determine recommendations regarding the installation of detectable warnings surfaces.
Washington Pedestrian Facilities Guidebook
Portland [Oregon] Pedestrian Design Guide
Oregon Bicycle and Pedestrian Plan
Florida Pedestrian Planning and Design Handbook
Massachusetts Pedestrian Transportation Plan
California Local Assistance Procedures Manual
Variety of recommendations
All of these guidelines recommended some type of tactile warning surface on curb-ramps. In addition, traffic-engineering professionals from Arizona, Minnesota, Georgia, New Jersey and South Carolina stated, in interviews, that there were state or local recommendations for a surface change on the curb ramp.
Portland, Oregon, and the States of Oregon, Washington, and Florida guidelines all suggest a texture change on the curb ramp to define the street edge for pedestrians who are visually impaired or blind. However, a truncated dome surface is not required. The Oregon Bicycle and Pedestrian Plan recommends that a diamond grid pattern be stamped on curb-ramps, and the Portland Pedestrian Design Guide recommends that curb-ramps be finished with heavy brooming parallel to the curb.
California requires grooves around the top of the curb ramp, truncated dome detectable warnings on the ramp surface where the slope is lower than 1:15, and a ½ in beveled lip at the curb line.
Other guidelines stated that a tactile warning was needed on the curb ramp but gave no guidelines for surface type.
ICC/ANSI A117.1-1998--Equivalent detectability
By 1998, based on recommendations of the ADAAG Review Advisory Committee which had recently been submitted to the Access Board for the revision of ADAAG, specifications for truncated dome detectable warnings at platform edges were included in the ANSI A117.1-1998 standard on accessibility. In this edition of ANSI A117.1, the texture and visual contrast specifications were the same as those in ADAAG. Alternatively, equivalent detectability could be provided by other means (ICC/ANSI A117.1-1998 705.3.2 and 705.3.3).
OTHER TEXTURED WALKING SURFACES
Other surfaces
A number of other textured surfaces are used on curb-ramps, but they have not been demonstrated to be highly detectable to pedestrians who are blind, both under foot and by the use of a long cane. Grooved cement has been found to be minimally detectable to people using a long cane as a travel aid, and it is even less detectable under foot. Other decorative surfaces that may be assumed to be detectable have not been tested for detectability. Many surfaces that look like they should be highly detectable have been found to be low in detectability.
Consistency in a warning surface is essential if it is to reliably be understood as a warning by pedestrians with visual impairments. The truncated dome texture specified in ADAAG 4.29.2 is the only surface that should be considered a detectable warning.
Raised design flooring
Raised design flooring sold as sheet goods or resilient tile may have a pattern of slightly raised circles. This product, sometimes known as Pirelli tile, is not highly detectable and should not be considered a detectable warning.
Directional tactile paving
Some countries have specifications for a raised, directional texture to guide people who are visually impaired. This texture is similar in height and width to truncated domes, but is a linear element. Such a directional texture should not be used as a warning.
Fig. Unnumbered. Photo is a top view of a tile having four raised, slightly rounded, flat-topped bars.
Fig. 1-6. Directional tactile tile (Armor-Tile). Photo is a low angle view of a thin epoxy polymer composite tile having raised bars. A micro-texture can be seen, which is intended to make the surface slip-resistant.
Fig. 1-7. Directional tactile tile (Detectable Warning Systems). Photo is a top view of one corner of a large sheet of resilient material with a raised bar texture.
TRUNCATED DOME DETECTABLE WARNINGS
Focus on truncated dome detectable warnings
This publication uses the term "detectable warning" to mean the walking surface consisting of truncated domes as specified in ADAAG.
The technical specification for detectable warnings in ADAAG is a truncated dome surface. Truncated domes are the only texture that has repeatedly been demonstrated to have excellent detectability to pedestrians who are bind, both under foot and through the use of a long cane. Therefore, the primary focus of this synthesis is on truncated dome detectable warnings. When the term "detectable warning" is used in this synthesis, it always refers to a truncated dome surface.
Fig. 1-8. Curb-ramps with truncated dome detectable warnings on opposite sides of an alley, Cleveland, OH. Photo shows detectable warnings on the entire surface of two curb ramps on opposite sides of a narrow alley. The flares do not have detectable warnings.
DETECTABLE WARNINGS IN ADAAG
Summary
This chapter presents specifications for detectable warning surfaces as specified in the Americans with Disabilities Act Accessibility Guidelines (ADAAG). It includes information on ADAAG technical provisions for detectable warnings at transit platform edges, on curb-ramps, preceding hazardous vehicular ways, and surrounding reflecting pools.
Chapter contents
This chapter covers the following topics.
Definition & specification / 21
Geometry of detectable warnings / 21
Detectable warnings at transit platform edges / 22
Detectable warnings at curb-ramps, at hazardous vehicular ways, and reflecting pools / 23
Definition of detectable warnings
A detectable warning is: "A standardized surface feature built in or applied to walking surfaces or other elements to warn visually impaired people of hazards on a circulation path." ADAAG 3.5
Detectable warnings are unique and standardized features, intended to function much like a stop sign. They alert pedestrians who are visually impaired to the presence of hazards in the line of travel, indicating that they should stop and determine the nature of the hazard before proceeding further.
Specification for detectable warnings
ADAAG specifies: "Detectable warnings shall consist of raised truncated domes with a diameter of nominal 0.9 in (23 mm), a height of nominal 0.2 in (5 mm) and a center-to-center spacing of nominal 2.35 in (60 mm) and shall contrast visually with adjoining surfaces, either light-on-dark or dark-on-light. The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact." ADAAG 4.29.2
Visual contrast
The appendix to ADAAG recommends that detectable warnings contrast visually with adjoining surfaces. "The material used to provide contrast should contrast by at least 70%. Contrast in percent is determined by: Contrast = [(B1 – B2)/B1] x 100 where B1 = light reflectance value (LRV) of the lighter area and B2 = light reflectance value (LRV) of the darker area. Note that in any application both white and black are never absolute: thus, B1 never equals 100 and B2, is always greater than 0." ADAAG A4.29
GEOMETRY OF DETECTABLE WARNINGS
Dome alignment & pattern
The detectable warning surface consists of truncated domes on a square pattern which are typically arranged in either of two configurations, diagonal alignment, and parallel alignment.
Figure 2-1 illustrates how both configurations can comply with the ADAAG specification for detectable warning. Depending on which configuration is used, the rows of domes will be aligned with, or at a 45° angle to the curb or platform edge, or the direction of travel. Pedestrians encountering either configuration will find the surface pattern equally detectable.
Another acceptable and plausible arrangement of truncated domes uses an equilateral triangular grid. Only one U.S. manufacturer has ever chosen to produce a detectable warning surface using this pattern.
Fig. 2-1. Patterns and alignments of truncated domes comprising the ADAAG detectable warning. The top portion of the drawing shows an overhead view of a truncated dome array in which the domes are arranged in a square pattern but the pattern is turned so that the sides of each square are diagonal to the direction of travel. This is referred to in this publication as diagonal alignment. It is the most common array in products currently in use in the U.S. The required 2.35" distance between domes is measured across the diagonal of the square. In the middle portion of the drawing, the same array has been rotated 45 degrees so that the sides of the squares are parallel with or perpendicular to the direction of travel. The bottom portion of the drawing shows an overhead view of an array in which the domes are arranged in a triangular pattern. The spacing between any two adjacent domes is always 2.35"
Dome profile
Fig. 2-2. Height and diameter of truncated domes used in ADAAG detectable warning. Drawing is a cross-section of one truncated dome, showing the .9" required diameter being measured at the bottom of the dome. The truncated dome is .2" high.
DETECTABLE WARNINGS AT TRANSIT PLATFORM EDGES
Requirement for transit platform edges (ADAAG 1991)
"Platform edges bordering a drop-off and not protected by platform screens or guardrails shall have a detectable warning. Such detectable warnings shall comply with [ADAAG] 4.29.2 and shall be 24 inches wide running the full length of the platform drop-off." ADAAG 10.3.1(8)
This requirement is applicable to new construction, alteration, and in key stations in existing transit facilities.
Fig. 2-3. Detectable warning used at platform edge bordering a drop-off. Drawing shows a small portion of a transit platform having a drop-off. There is a 24" deep strip of detectable warning along the platform edge.
Why the warning is placed at the platform edge
The rationale for placement of detectable warnings as required by ADAAG was as follows. Advocates wanted the warning to be at or very near the platform edge so that there would be no possibility that a traveler could interpret a width of platform between the warning and the edge as a safe place to stand. Transit managers wanted the warning to be at the edge so that on platforms that were retrofitted with detectable warnings, there would be sufficient platform width on the side away from the edge to accommodate a typical rush hour number of riders without the necessity for riders to stand on the warning due to crowded conditions.
Why the warning is 24 inches wide
The rationale for the width of detectable warnings required by ADAAG was the following. Twenty-four in (610 mm) had been repeatedly demonstrated to be a sufficient width of a surface highly detectable both under foot and by use of a long cane, to enable detection and stopping on that surface by most blind travelers (Peck & Bentzen, 1987; Templer & Wineman, 1980; Templer, Wineman & Zimring, 1982).
Transit managers wanted the warning to be as narrow as possible. They did not want riders to either stand and wait on the warning, or travel on it while no train was at a platform. Therefore a warning surface needed to: reduce the effective standing capacity of platforms as little as possible; enable blind passengers to stop a safe distance from the platform edge without having to contact the edge to determine where it was; and demarcate the limit of the safe waiting area for all passengers.
Transit managers reasoned that while most passengers would wait behind the warning most of the time, there would nonetheless be a small minority of passengers who would choose to walk along the warning, between the edge and waiting passengers, if the warning was wider than 24 in (R. Weule, BART Safety Manager, personal communication, 1986).
Width & placement decision also based on positive experience
Also contributing to the rationale for ADAAG specifications regarding both width and placement of detectable warnings on transit platform edges was a decrease in accidents for all riders on BART (McGean, 1991) and Metro Dade (A. Hartkorn, Metro Dade Safety Manager, personal communication, 1994) in the years following installation of 24 in wide detectable warnings at platform edges in those systems.
Fig. 2-4. Detectable warning surface at MARTA Station, Atlanta, GA. Photo is looking down the length of a MARTA platform. The detectable warning can be seen beginning immediately at the platform edge and extending back 24". Beyond the detectable warning, farther from the platform edge, is a 12" deep strip of granite. The rest of the platform is relatively smooth pavers
DETECTABLE WARNINGS AT CURB-RAMPS, HAZARDOUS VEHICULAR WAYS AND REFLECTING POOLS
Requirement at curb-ramps
"A curb ramp shall have a detectable warning complying with [ADAAG] 4.29.2. The detectable warning shall extend the full width and depth of the curb ramp." ADAAG 4.7.7. (Temporarily suspended April 12, 1994, July 29, 1996, and November 23, 1998)
Fig. 2-5. Florida curb ramp complying with ADAAG 4.7.7. Photo shows an apex curb ramp having a detectable warning on the entire surface of the ramp. The sidewalk is brick pavers.
Requirement at hazardous vehicular ways
"If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning which is 36 in (915 mm) wide, complying with 4.29.2." ADAAG 4.29.5 (Temporarily suspended April 12, 1994, July 29, 1996, and November 23, 1998)
Fig. 2-6. Example of detectable warning at a level rail crossing (a type of hazardous vehicular way). Drawing shows a sidewalk with rails running across it. There is no curb or detectable boundary of any kind to indicate that the pedestrian will encounter rails. However, a 36" deep detectable warning is placed parallel to each outer rail, about 24" from the rail.
Requirement at reflecting pools
"The edges of reflecting pools shall be protected by railings, walls, curbs, or detectable warnings complying with [ADAAG] 4.29.2." ADAAG 4.29.6 (Temporarily suspended April 12, 1994, July 29, 1996, and November 23, 1998).
RECENT RESEARCH ON DETECTABLE WARNINGS
Summary
This chapter summarizes research to answer questions about the need for and effectiveness of detectable warnings for people who are blind or visually impaired and the effects of detectable warnings on pedestrians with mobility impairments. The chapter then describes research on visual contrast and sound contrast. It concludes with further research on detectability and discriminability conducted in Japan and the United Kingdom.
Chapter contents
This chapter covers the following topics.
Effects of curb-ramps on blind pedestrians / 26
Effects of detectable warnings on travel by blind pedestrians / 26
Effects of detectable warnings on people with mobility impairments / 27
Evaluation of detectable warning materials / 28
Research on sound on cane-contact differences / 29
Research on visual contrast / 29
Research on detectability / 30
Research on dome dimensions and spacing / 30
EFFECTS OF CURB-RAMPS ON BLIND PEDESTRIANS
Effect on street detection
Two research projects (Barlow & Bentzen, 1994; Bentzen & Barlow, 1995; Hauger, Safewright, Rigby & McAuley, 1994) confirmed that removal of the single reliable cue to the presence of an intersecting street, that is, the down curb, did result in the inability of even skilled, frequent blind travelers to detect some streets. Barlow and Bentzen found that on 35% of approaches to unfamiliar streets, blind travelers using a long cane failed to detect the presence of an intersecting street before stepping into it. Hauger et al. found failure to detect streets on a somewhat smaller percentage of trials.
Effect of slope & placement
Both projects (Barlow & Bentzen, 1994; Hauger et al., 1994) found that failure to detect streets was highly correlated with slope of the curb ramp. Barlow and Bentzen also found that street detection was correlated with the abruptness of change in angle between the approaching sidewalk and the curb ramp. Both projects found that street detection was more likely when curb-ramps were at the apex of a corner than when they were in the line of travel. Hauger et al. also found that apex curb-ramps were more likely to lead to unsuccessful street crossings than perpendicular curb-ramps.
Fig. 3-1. Where there is no difference in slope or elevation between the sidewalk and street, it is particularly difficult for pedestrians who are blind to determine when they have reached an intersecting street. Blended curb in Sacramento, CA. Photo shows a blended curb where asphalt of the adjoining street has been raised to curb level at a corner. There are trolley tracks in the parallel street
EFFECTS OF DETECTABLE WARNINGS ON TRAVEL BY BLIND PEDESTRIANS
Detectable warnings are helpful at curb-ramps
Hauger et al. (1994) obtained subjective data from 70 research participants who were blind or who had low vision, indicating that detectable warnings were judged to be helpful. In the same project, raters viewing videotapes of the 70 participants as they crossed intersections with and without detectable warnings on curb-ramps, found that a higher proportion of unsuccessful crossings occurred where there were no detectable warnings than where there were detectable warnings.
They also found that the visual contrast of detectable warnings helped participants with low vision establish and maintain a heading toward the opposite corner. Participants using dog guides may also have been aided by the visual contrast that the dog guides appeared to head for.
Hughes (1995) conducted research in which 17 participants who were totally blind or who had low vision traveled up and down laboratory ramps having eight different tactile surfaces, of which five were truncated domes. Ten of the participants then responded to structured interviews including questions about their perception of the tactile surfaces. Nine said use of tactile surfaces on curb-ramps would increase their safety. Six said that use of the tactile surfaces would make them more likely to travel by foot.
Detectable warnings reduce falls at transit platform edges
During the seven years following the installation of detectable warnings on all platform edges in the BART system, platform edge accidents decreased for all riders, but especially for riders having visual impairments (McGean, 1991). In San Francisco, riders in stations having different platforms serving both BART and Muni (San Francisco Municipal Railway) were observed to stand at different distances from the platform edge. On BART platforms, which had 24 in detectable warnings along the edges, passengers tended to wait behind the warning, that is, at least two feet from the edge. On MUNI platforms, which did not have detectable warnings, passengers waited closer to the edge (McGean, 1991).
EFFECTS OF DETECTABLE WARNINGS ON PEOPLE WITH MOBILITY IMPAIRMENTS
Effects on transit platforms
Objective and subjective research confirm that truncated dome detectable warnings at transit platform edges do not adversely affect people having a variety of mobility impairments. None of the 24 participants in research by Peck and Bentzen (1987) in BART had any difficulty maneuvering across or along truncated domes or turning on truncated domes. Participants in this Peck and Bentzen research reported that truncated domes would have minimal effects on their travel in BART. A few people who used canes or crutches said they felt their aids would be less likely to slip as they exited trains onto the truncated dome surface than onto smoother surfaces.
Effects at slopes or curb-ramps
Objective and subjective research confirm that truncated dome detectable warnings on slopes or curb-ramps have minimal adverse effects on people with mobility impairments. Bentzen, Nolin, Easton, Desmaris and Mitchell (1993, 1994b) videotaped 40 participants having those mobility impairments which made them most likely to have difficulty on bumpy, sloping surfaces, travel up and down, stopping, starting, and turning on nine ramps (slope 1:12) having nine different truncated dome surfaces and one ramp surfaced with brushed concrete. Video raters observed minimal evidence of increased effort, slipping, loss of stability, or wheel or tip entrapment on this challenging task. Participants in this Bentzen et al. (1993, 1994b) research reported minimal effects of truncated domes relative to the brushed concrete surface.
Hughes (1995) had nine people with mobility impairments travel up and down eight ramps with different tactile surfaces. No individuals reported or were observed to have problems with directional control, stability, effort or discomfort that would have altered their ability to travel safely.
Benefits at curb-ramps
Hauger et al. (1994) had 30 participants with mobility impairments travel up and down curb-ramps with and without truncated domes. A majority felt that they were safer, had better traction, and were more stable on ramps having truncated domes than on concrete ramps. Forty four percent of participants said it required less effort to negotiate up and down the ramps with detectable warnings than the concrete curb-ramps; 23% said the reverse. Some wheelchair users said it was easier to find and steer toward the up-ramp on the opposite corner when it had the contrasting detectable warning surface.
Fig. 3-2. Stamped concrete detectable warning on curb ramp, Austin, TX. Photo shows a person in a wheelchair going down a perpendicular curb ramp that has a 4’ wide by 5’ deep detectable warning made of stamped concrete.
Effects at hazardous vehicular ways
Hauger et al. (1994) observed pedestrians at three commercial sites where shopping carts were used and where detectable warnings were installed to separate the pedestrian and vehicular ways. In 12 hours of observation, more than 1,500 pedestrians crossed the detectable warnings. No significant incidents or problems were observed for the general public, which included persons with mobility impairments, shopping carts, shopping carts with children, large gurneys, and baby carriages.
EVALUATION OF DETECTABLE WARNING MATERIALS
Laboratory testing
Eighteen truncated dome materials were submitted to laboratory testing under a project sponsored by the Federal Transit Administration (Ketola, N. & Chia, D., 1994). Standard tests were performed for impact resistance, wet and dry slip resistance, wear resistance, high-pressure hot water resistance, and adhesion/bond strength after 55 hours soaking in water.
Impact tests under room temperature, hot and cold conditions found that, in general, rubber-based and polymer composite materials performed quite well; more rigid products (cementitious or ceramic tile) performed poorly. All materials exceeded the minimum value for slip resistance recommended by the Access Board under both wet and dry conditions. Wear resistance tested by 30 seconds of sandblasting revealed a wide variety in performance of materials. High pressure hot water testing revealed little difference among products. Seven materials were found to have poor adhesion/bond strength. Detailed results of laboratory testing are in Ketola and Chia, 1993.
Field testing
Eight of the surfaces subjected to laboratory testing were field tested in high pedestrian traffic indoor and outdoor areas in stations of three rail transit systems, the MBTA (Boston), GCRTA (Cleveland), and SEPTA (Philadelphia) (Ketola & Chia, 1994). Evaluations included installation and maintenance, wear resistance, maintenance of bond, resistance to cracking and chipping, and maintenance of color.
Proper installation was found to be crucial to good performance. Factors affecting adequacy of installation included installer skill, ambient conditions, surface preparation, application of material and setting period. No transit system reported maintenance problems with any material. No transit system reported any difficulty removing snow and ice from any materials using the same tools and chemicals used on the rest of the platform surface. Although materials differed in wear resistance, all were estimated to have a relatively long useful life.
Materials differed widely in maintenance of bond; four materials had some bond failure. Materials differed greatly in resistance to cracking and chipping; two materials had no instances of cracking and chipping, and two had repeated instances. Three materials showed no color change indoors or outdoors; one material showed major color change.
Fig. 3-3. Installation of detectable warning test surfaces at MBTA’s South Station, Boston, MA. Photo shows a corridor with 24" deep detectable warning materials running all the way across it at regular intervals.
RESEARCH ON SOUND ON CANE-CONTACT DIFFERENCES
A test of difference in sound
Although ADAAG 4.29.2 requires that detectable warning surfaces used indoors differ in sound on cane-contact, there has been no attempt to quantify the amount of difference in sound. Bentzen and Myers (1997) did, however, test four truncated dome products installed on an outdoor light rail platform in Sacramento for differences in sound on cane-contact.
Surfaces differed from one another in both objective and subjective measures of differences in sound on cane-contact between the adjoining platform of pavers and the detectable warnings. Difference in sound between the warning surface and the adjoining platform surface appears to be related to both the detectable warning material and the way in which it is installed. The detectable warning material installed with a slight gap between the warning and the substrate was most detectable on both objective and subjective measures.
Contrast of detectable warnings
ADAAG 4.29.2 requires that detectable warnings contrast visually with adjoining surfaces, either dark on light, or light on dark. A 70% contrast in light reflectance between a detectable warning and an adjoining surface is recommended in the Appendix (A4.29.2).
Research shows value of safety yellow
Recent research indicates that the color safety yellow is so salient— even to persons having very low vision—that it is highly visible even when used in association with surfaces having light reflectance values differing by as little as 40% (new, gray-white concrete) (Bentzen, Nolin, and Easton, 1994a). A safety yellow detectable warning surface having a 40% reflectance difference from new concrete was subjectively judged more detectable than a darker warning surface which contrasted with new concrete by 86% (Bentzen et al., 1994a). Hughes (1995) found that yellow or yellow-orange warning surfaces were preferred over black warning surfaces.
Standards for safety yellow
Safety yellow is a color that is standardized for use as a warning in the pedestrian/highway environment.
U.S. —ANSI Z535.1-1991, 6.3
Internationally—ISO 3864-1984(E)
Many truncated dome surfaces
Following publication of ADAAG in 1991, numerous manufacturers entered the market. The products differed slightly in execution of the truncated dome dimensions and spacing as well as materials (see Chapter 7). Truncated dome products soon included resilient sheet material, dimensional pavers, tiles, polymer composites, bricks, pre-cast concrete, stamped concrete and applied surfaces.
Many truncated dome surfaces found to be highly detectable
In 1994 the Federal Transit Administration sponsored laboratory research (Bentzen, Nolin, Easton, Desmarais & Mitchell, 1994) to evaluate the detectability of truncated dome surfaces that differed in material, dome dimensions, and dome spacing. Thirteen surfaces representing the extremes as well as the midpoints of dome dimensions and dome spacing were tested by 24 blind participants for under foot detectability in association with four transit platform surfaces varying in roughness and resiliency. Each detectable warning surface was paired with brushed concrete, coarse exposed aggregate concrete, Pirelli tile, and wooden decking.
Detection rate was greater than 95% for all but one warning surface (a prototype that was not offered for sale).
Factors which have little effect on detectability
A number of factors were found to have little or no effect on detectability.
Parallel vs. diagonal alignment of domes
Differences in resiliency
Additional small elements added to increase slip resistance
Irregularities in spacing where domes in adjoining tiles or pavers were
somewhat closer together or farther apart than within the tiles or
pavers
A gradual increase in dome height within the first several inches
Factor which decreases detectability
Detectability of truncated dome warning surfaces was less when the warning was installed in association with coarse exposed aggregate concrete.
RESEARCH ON DOME DIMENSIONS AND SPACING
Japanese research
Dome (raised dot) height, diameter and spacing were investigated to determine optimal dome dimensions and spacing. (Report of fundamental research on standardization relating to tactile tiles for guiding the visually impaired, 1998). For testing dome height, 60 participants walked from smooth tiles, across domed tiles of different heights, and were asked to report whether they detected a domed tile under foot. For testing dome diameter and spacing, 60 blind participants walked from smooth tiles, across either domed tiles or directional (bar) tiles having different dimensions, and reported whether tiles had domes or a directional (bar) pattern. (See Fig. 4-3 for the nine diameters and spacings tested.). Participants also rated tiles for ease of identifying them as either dome or directional tiles.
Dome height tests
Dome heights tested were 0 mm, 2.5 mm, 5.0 mm, 7.5 mm and 10 mm. All participants detected tiles having 5.0 mm high domes. Fifteen percent of participants could not detect tiles having 2.5 mm high domes. Some participants stumbled when traversing tiles having 10 mm high domes. Five mm high domes were recommended.
Dome diameter and spacing tests
Dome base diameters tested were (22 mm, 28 mm, and 35 mm), and dome spacings were (42.9 mm, 50 mm, and 60 mm). Top diameter of domes was always 10 mm less than bottom diameter. Dome spacing was measured on centers parallel to one side of a square pattern.
Optimal dome diameter and spacing combinations
Three tiles had identification rates greater than 90% and were also rated easy to identify:
22 mm base diameter with 50 mm spacing;
22 mm base diameter with 60 mm spacing; and
28 mm base diameter with 60 mm spacing.
ILLUSTRATIONS OF INTERNATIONAL TACTILE GROUND SURFACE INDICATORS
Fig. 3-4. Warning pavers at a raised crosswalk. United Kingdom. Drawing shows a wide raised crosswalk. The crosswalk is made of brick pavers, and is bordered on each side with light colored pavers. On the sidewalk at each end of the crosswalk is a 4’ deep area of detectable warning extending the full width of the crosswalk.
Fig. 3-5. Detectable warning at top & bottom of stairs, exterior use in Australia. Photo shows a wide exterior stairway leading from a building, down to a walk on a lower level. A strip of detectable warning 2’ deep, and running the full width of the stairs, is placed one tread-width away from the top and bottom riser. The stairs have a contrasting nosing. The detectable warning and stair nosing have good visual contrast from the darker pavers of the stairs and landing at the top.
Fig. 3-6. (Left) Detectable warnings (blister surface) on the three curb-ramps at a splitter island, Ireland. Photo shows a small, triangular splitter island with a curb ramp on each side having detectable warning. Beside each curb ramp is a pedestrian pushbutton. The pushbuttons are of a type on which walk/wait information can be read on a panel near the top of the pushbutton housing.
Fig. 3-7. (Right) Tactile ground surface indicators leading away from stairs, Louvain, Belgium. Photo shows a linear directional surface along a wide paved area in front of stairs going up; the directional surface is perpendicular to the risers. Directly in front of the stairs, the same type of linear, directional surface leads perpendicularly from the first directional surface, to the stairs. At the "T" junction of the directional surfaces is a non-textured square, having high visual contrast.
INTERNATIONAL USE OF WARNING SURFACES
Summary
This chapter includes information on approaches to use of tactile ground surface indicators, including warning surfaces. Information on selected countries having significant experience in the application of warning surfaces is presented. Each entry includes the history, specifications or guidelines for textures and locations, maintenance and durability, and acceptance.
Chapter contents
This chapter covers the following topics.
Different approaches / 34
Japan / 35
United Kingdom / 36
Australia / 39
New Zealand / 41
Italy / 42
France / 44
Germany / 45
Austria / 46
Netherlands / 48
International standardization / 49
Common conversions (inches are rounded figures)
5 mm = 0.2 in
25 mm = 1 in
50 mm = 2 in
60 mm = 2.35 in100 mm = 4 in
200 mm = 8 in
300 mm = 12 in
500 mm = 20 in600 mm = 24
1200 mm = 47
1800 mm = 71
2 m = 79 in
Tactile ground surface indicators
Worldwide, a number of ground or floor surfaces have been used to provide different types of information to people who have visual impairments. In the work of the International Organization for Standardization (ISO), these surfaces are referred to as tactile ground/floor surface indicators or TGSIs.
TGSIs as a wayfinding system
In many countries, TGSIs are conceptualized as providing a comprehensive wayfinding system for people with visual impairments. In implementing this approach, extensive use is made of linear surfaces that provide guidance from one place to another such as between the stairs and the platform edge in a transit station. Surfaces that are similar to the detectable warning surface in the U.S. are designated as "attention fields," and are typically used at path intersections, at curb-ramps (especially mid-block), or at turns, as well as at platform edges and curb-ramps. Japan, Austria, Switzerland, France and Italy take this approach.
Fig 4-1. "Attention field" surface shown circled here, and in Fig. 4-2. Drawing shows a square of truncated dome surface, an "attention field," marking the "T" intersection of linear textured tactile paths.
Fig. 4-2. Wayfinding system of linear surfaces and attention fields in Austrian subway system. Drawing shows system of tactile paths leading from top of stairs on subway platform to and along the platform edges, and to an information point. At each path intersection, there are truncated dome attention fields.
TGSIs to indicate a variety of features
In the United Kingdom, seven different tactile ground or floor surfaces are used to help people who are visually impaired recognize different types of features in the environment. Different surfaces are used to indicate crossing points (curb-ramps), hazards (steps, ramps, entrances to transit platforms), indoor transit platform edges, outdoor transit platform edges, segregated shared bicycle/pedestrian surfaces, and amenities such as public telephones and ticket offices. A linear surface is also used as a guidance path.
TGSIs for warnings & directional information
Some countries, including Australia, New Zealand and Canada use warning surfaces (truncated domes) only where there are vehicular hazards or drop-offs. They also use linear directional surfaces where directional cues such as grasslines, curbs, hedges, fences, or walls are not present.
U.S. approach to warning surfaces
In the U.S., (although opinions vary), the prevailing attitude as articulated in standards and guidelines, is that warning surfaces are needed primarily at highly hazardous locations where there is no definitive cue denoting the boundary between pedestrian and vehicular ways (curb-ramps and hazardous vehicular ways), or where there is a drop-off (platform edges, reflecting pools and stairs). It is recognized that people who are blind are usually able to negotiate these hazards safely, using their normal travel aids such as long canes or dog guides, especially when they are in familiar areas. Detectable warnings can provide information about the presence, location and direction of hazards that is useful to blind pedestrians traveling in unfamiliar places. Detectable warnings can also provide confirming cues about the environment for pedestrians who may not have highly developed travel skills.
U.S. approach to directional surfaces
There has been limited use of directional surfaces in the U.S. for such purposes as guidance across wide or skewed intersections, or guidance to a curb ramp. Most of this experience has been in San Francisco, Sacramento and San Diego, CA. No standards or guidelines have ever been established in the U.S. for the use of directional surfaces. In the U.S. it is not considered necessary to provide a comprehensive tactile wayfinding system for people who have visual impairments. Blind pedestrians are instead taught to extract clues from the environment, using natural guidelines provided by such features as grasslines, fences, hedges, building lines and traffic.
History of use
Tactile warning and guidance surfaces have been used in Japan since 1967. Use began in Okayama Prefecture and is now widespread throughout Japan. Tactile warning and guidance surfaces are used on platforms and top and bottom of stairs in almost 100% of transit station in metropolitan areas. They are also used at curb-ramps and on sidewalks. There is on-going research to determine optimal dimensions for truncated dome warning and linear directional surfaces (Murakami, Aoki, Taniai, & Muranaka, 1982; Murakami, Ohkura, Tauchi, Shimizu, & Ikegami, 1991; Report of fundamental research on standardization…, 1998).
Most common texture
Texture is not standardized; dome shape, diameter and spacing varies. This is the Most common texture
Dome height—5 mm (all warning surfaces)
Dome base diameter—35 mm
Inter-dome spacing—50 mm with parallel or diagonal alignment
Guidelines for location of warning surfaces
Guidelines are contained in Guidelines for Installation of Tactile Guide Blocks for the Visually Impaired and Commentary (1985). These are guidelines only; dimensions are given in only a few instances, but there are numerous illustrations.
Curb-ramps—600 mm deep, about 300 mm from the street, the full width of the associated crosswalk
Islands—on islands wherever a crosswalk contacts an island, 600 mm deep, about 300 mm from the street, the full width of the associated crosswalk
Products
Products used for warning surfaces are
Stone
Concrete
Synthetic rubber
Plastic resin
Vinyl chloride
Durability and maintenance
Durability and maintenance of warning surfaces are not considered problems in Japan. Heavily traveled warning surfaces wear out regardless of the material. Color changes, splitting of tiles, falling off of tiles, and deterioration of domes sometimes occur. Snow and ice area not normally removed. Synthetic rubber and vinyl chloride are very slippery when wet.
Acceptance
Warning and guidance surfaces are well accepted in Japan. Many Japanese persons with visual impairments depend on warning and guidance surfaces. Persons with mobility impairments accept them. There are few complaints from persons who are elderly. There are few complaints from bicyclists.
Information provided by
Masaki Tauchi, Ph.D. Okayama Prefectural University
111 Kuboki, Soja-shi
Okayama 719-11, Japan
Tel: +81 866-94-2188
Fax: +81 866-94-2206
E-mail: mtauchi@fhw.oka-pu.ac.jp
Fig. 4-3. Japanese research varied the size of truncated domes (dot diameter) and the spacing interval between domes (dots). Of the nine detectable warning test surfaces, three (shown enclosed by the line) were identified as dot (versus bar) tiles on at least 90% of trials. Drawing shows an overhead view of a 3 x 3 array of surfaces, the factorial combination of three dot diameters with three dot spacings. Dot diameters are 22, 28 and 35 mm. Intervals between domes, measured on the side of a square, are 42.9, 50 and 60 mm. The three dome diameter and spacing combinations that had identification rates greater than 90 were: 22 mm base diameter with 50 mm spacing; 22 mm base diameter with 60 mm spacing; and 28 mm base diameter with 60 mm spacing.
History of use
Domed warning (blister) surfaces have been used on curb-ramps and at at-grade crossings in the UK since 1986. The domed surface for warning was changed to a truncated dome surface because it was more comfortable, particularly for persons with mobility impairments associated with arthritis. Extensive research has been conducted on detectability, discriminability and memory for seven different tactile paving surfaces to provide a warning at curb-ramps, at stairs and ramps, at off-street transit platform edges, and at on-street transit platform edges, to provide guidance along a route, to provide information about a segregated cycle/pedestrian way, and to provide information about the location of amenities such as public telephones (Gallon, 1992; Gallon, Oxley & Simms, 1991; Savill, Davies, Fowkes, Gallon & Simms, 1996; Savill, Stone & Whitney, 1998).
Texture
Specifications for the blister surface and its use first were adopted in 1986. They were revised in 1991 (Disability Unit Circular 1/91).
Dome height—5 mm ± .5 mm
Dome base diameter—25 mm
Domes 64-67 mm apart with parallel alignment.
Locations of tactile paving surfaces
Extensive guidance on the location and installation of six different tactile paving surfaces is contained in Guidance on the use of tactile paving surfaces (1998), which supercedes Disabilitiy Unit Circular 1/91). Each surface is to be used for a different purpose.
Pedestrian crossing points where the sidewalk is flush with the street
Hazards including stairs, level crossings and the approach to light rapid transit platforms
The edge of off-street rail platforms
The edge of on-street rail platforms
A shared cycle track/footway surface and central delineator strip
Guidance along a route where traditional cues such as property lines or curbs are not available
Sidebar:
"It is vitally important that the removal of any existing kerb upstand at a recognized crossing point, is accompanied by the installation of the blister surface." Guidance on the Use of Tactile Paving Surfaces (1998)
Warning surface at curb-ramps, medians, and raised crosswalks
Guidance on the installation of truncated domes (blister surface) on curb-ramps, medians, and raised crosswalks is as follows.
Depth of installation varies with nature of crossing, 400-1200 mm across curb ramp, with stem (1200 mm wide) to the building line at signalized crossings
On medians greater than 2 m wide, warning surface required for depth of 800 mm at each side
On medians less than 2 m wide, warning surface required for entire depth of median
On the sidewalk at both ends of raised crosswalks.
Red normally used at signalized crossings
Buff (or any color other than red, which contrasts with surrounding pavement) normally used at unsignalized crossings
Warning surface at off-street transit platform edges
Specifications for truncated domes and guidance on their installation on off-street transit platform edges are as follows.
Dome height—5 mm ± 0.5 mm
Dome base diameter—22.5 mm
Installation—400 mm deep, installed 500-700 mm from platform edge
Other warning surfaces
Two additional warning surfaces are recommended for other purposes. At on-street platform edges: a surface comprised of small raised lozenge shapes running in the direction of the platform edge is installed at a depth of 400 mm, 500-700 mm from the platform edge. At stairs, level crossings and the approach to light rapid transit platforms: an 800 mm deep "corduroy" surface is required.
Products for curb-ramps and transit platforms
The following materials are typically used for warnings at curb-ramps and transit platforms.
Pre-cast concrete pavers
Natural stone
Other materials are currently being investigated.
Products for other applications
Typical products
Rubber tile
Vinyl
Occasionally used for special purposes
Hardwood
Aluminum
Stainless steel
Brass nails
Fig. 4-4. Brass nails installed in pavement as detectable warnings. Photo shows an area of detectable warning surface about 2’ deep by 4’ long that is formed by inserting brass nails with large, rounded heads into the sidewalk pavers along a curb line. One sneaker-clad foot can be seen on the domes.
Durability
In heavily trafficked areas, modules need occasional replacement to maintain the detectable texture.
Slip Resistance
There is no evidence that surfaces are slippery under any conditions.
Acceptance
Acceptance of truncated dome detectable warnings (blister surfaces) is good. They are reported to be helpful to people with visual impairments. Some people having mobility impairments report having difficulties, therefore the extent of the surface is limited. No adverse impact has been reported for the general public.
Information provided by
Sue Sharp, Disability Policy Branch, Mobility Unit Dept. of the
Environment,
Transport and the Regions
Floor 1/11, Great Minster House
76 Marsham St.
London SW1P 4DR, England
Phone: +44 (0) 171 890 4917
Fax: +44 (0) 171 890 6102
E-mail: sue_sharp@detr.gsi.gov.uk
Peter Barker, Manager, Joint Mobility Unit
Royal National Institute for the Blind
224 Great Portland St.
London W1N 6AA, England
Phone: +44 (0) 171-387 2233
Fax: +44 (0) 171-388 3160
E-mail: Pbarker@rnib.org.uk
History of use
Truncated dome warning surfaces have been specified since 1988, but not required under the Building Code of Australia until 1999 (AS 1428.4 Design for access and mobility—Tactile ground surface indicators for the orientation of people with visual impairment). Warning surfaces are required at curb-ramps, medians, stairs, ramps, escalators, around overhead obstacles under 2000 mm in height from the floor, and at main entrances to buildings where there is no curb separating the pedestrian from the vehicular way. Warning surfaces are also becoming common at bus and trolley stops, railway platforms and wharves
Specifications: two types
Type A
Dome height—4 to 5 mm
Dome base diameter—23 ± 1 mm
Dome top diameter—11.5 ± 1 mm
Dome spacing—60 ± 1 mm apart, measured on the diagonal, with diagonal alignment
Type B—recommended for outdoor use
Dome height—4 to 5 mm
Dome base diameter—35 ± 1 mm
Dome top diameter—25 ± 1 mm
Dome spacing—50 ± 1 mm apart, with parallel alignment
Location
Warning surface locations are specified in the Building Code of Australia.
At curb-ramps: placed 300 mm back from the curb line, 600 mm deep, and the width of the ramp.
At medians and islands: placed 300 mm back from the curb line, 600 mm deep, and the entire width of the curb-ramp or cut-through.
At high use vehicular areas such as parking lots: placed 300 mm back from the driveway, 600 mm deep, and full width of the pathway.
At transit platforms: placed 600 to 900 mm from platform edge, 600 mm deep
At bus stops: placed 300 mm back from the edge of the road, 600 mm deep and 1800 mm wide
At tops and bottoms of stairways and escalators: one tread width from riser, 300 ± 10 mm deep for enclosed stairways and escalators, and 600 ± 10 mm deep for unenclosed stairways and escalators
Fig. 4-5. (Left) Australian curb ramp with detectable warning. Photo shows detectable warning pavers extending almost all the way across a curb ramp. They are 4’ wide by 2’ deep, set 1’ back from the street.
Fig. 4.6. (Right) Curb ramp leading to handicapped parking space, Australia. Photo shows a 2’ deep X 4’ wide strip of truncated dome detectable warning placed about one foot back from the curb line, at a crosswalk leading from an accessible parking space onto a sidewalk.
Products
Concrete—must be 60-70 MPa (8,700-10,000 psi) in strength to maintain luminance contrast in wet weather and to produce strong, durable domes.
Vitrified porcelain
Synthetic rubber/vinyl
Polymer plastic—on trial
Layers of reflective paint—on trial
Durability
Concrete and vitrified porcelain are durable, but domes can be damaged when snowplows are not set carefully. Synthetic rubber/vinyl is subject to damage. Methacrilate resin cracks and chips.
Acceptance
People with visual impairments find them helpful provided they have some instruction in their use. Major organizations of and for people with mobility impairments agree that rises of 5 mm can be negotiated without difficulty. Truncated domes are not used in "Aged Care Residential Facilities" as they could be hazardous to residents who shuffle. Also, residents become familiar with layout of their residences and do not need warnings. The general public experiences no problems. When used to warn of overhead protrusions where there is no barrier, they protect all pedestrians.
Information provided by
Murray Mountain, Access Design Solutions
103 New Street
Brighton, Victoria
Australia 3186
Phone: +61 3 9593 3750
Fax: +61 3 9592 9071
Mobile: 0414 589 414
E-mail: mountain@alphalink.com.au
Fig. 4-7. Detectable warning surface across full width of sidewalk at an alleyway (hazardous vehicular way) in Australia. Photo shows a wide sidewalk that slopes down to be completely blended with a driveway. A 24" deep strip of detectable warning pavers extends the full width of the blended curb. It is separated from the driveway by a 12" wide painted line.
History of use
Truncated dome warning surfaces and guidance surfaces have been in use in New Zealand since 1990. They have been required since 1993 under NZS/AS 1428.4 Design for access and mobility—Tactile ground surface indicators for the orientation of people with visual impairment. Most local authorities are using warning surfaces at intersections.
Texture of warning surface
Specified by NZS/AS 1428.4 and Land Transport Safety Authority Standards RTS 14 (June 1997)
Type A
Dome height—4 to 5 mm
Dome base diameter—23 ± 1 mm
Dome top diameter—11.5 ± 1 mm
Dome spacing—60 ± 1 mm apart, measured on the diagonal, with diagonal alignment
Type B—(preferred in New Zealand)
Dome height—4 to 5 mm
Dome base diameter—35 ± 1 mm
Dome top diameter—25 ± 1 mm
Dome spacing—50 ± 1 mm apart, with parallel alignment
Location
Warning surfaces are required
At curb-ramps: placed 300 mm back from the curb line, 600 mm deep, and the width of the ramp
At medians and islands: placed 300 mm back from the curb line, 600 mm deep, and the entire width of the curb-ramp or cut-through
At high use vehicular areas such as parking lots: placed 300 mm back from the driveway, 600 mm deep, and 600 mm min. wide
Products
Precast concrete
Synthetic rubber
Cobble stone with truncated domes
Maintenance and durability
Concrete is extremely durable and maintenance-free. There are some maintenance problems with synthetic rubber. There has been minimal experience with snow removal, but this does not seem to be a problem. Surfaces are not slippery in wet or dry conditions.
Acceptance
Positive feedback from people with visual impairments has been received for 10 years. People with mobility impairments have a strong preference for Type B warnings. No complaints by general public have been received except when tiles are not installed flush with the ground surface. General recognition of tactile tiles at crossing points has increased awareness of general population, making these crossing points safer. People with multiple disabilities consider them helpful. People who are elderly report that they are helpful.
Fig. 4-8. Diagram showing requirements for guidance surface and detectable warning on curb-ramps in New Zealand. Drawing shows curb ramp for mid-block crossing. A 24" deep detectable warning extends across the width of the curb ramp and is placed 12" back from the curb line. A 24" wide linear surface intersects the middle of the detectable warning and extends from the detectable warning to the far side of the sidewalk so that a pedestrian walking down the block would encounter the linear surface and could follow it to locate the curb ramp.
Information provided by
Michael Browne, Mobility Research Centre
P.O. Box 9518, Newmarket
Auckland, New Zealand
Phone: +64 520-4953
Fax: +64 524-4177
History of use
A tactile warning surface, "Loges," exhibited in Düsseldorf, Germany was introduced in Italy in 1997. Loges is now used in 20 cities. Locations include subway stations, railway stations and post offices.
Texture of domes
A handbook describes the texture characteristics (Orientation and safety guide-strip: Designer’s handbook).
Full domes 5 mm high having diagonal alignment are used as a warning.
Truncated domes 5 mm high having diagonal alignment are used to signal a
danger that can be safely overcome.
Dome base diameter—22 mm
Dome spacing—55 mm with parallel arrangement
Location
Distance of warning surface from the indicated danger varies.
Placed 300-400 mm back from a danger that can be crossed
Placed 500-700 mm back from a danger which cannot be crossed
Depth of warning—400 mm
Products
Commonly used materials are:
Concrete (exterior use)
Rubber (interior use)
Reconstructed stone (areas of artistic or historic significance)
Stoneware
Maintenance, durability and slip resistance
Maintenance and durability are not considered to be a problem. Surfaces are as easy to maintain as other paving or flooring surfaces. Surfaces are as durable as other paving or flooring surfaces. Surfaces do not become slippery.
Acceptance
Warning surfaces are well accepted in Italy. Blind pedestrians find them very helpful. Blind pedestrians consider that warning surfaces promote a positive image of pedestrians with visual impairments, as they travel with greater independence and confidence. People having mobility impairments do not find them troublesome.
Information provided by
Antonio Quatraro, Counselor in the domain of the integration of the
visually impaired.
Via L. Fibonacci 9 50131
Firenze, Italy
Phone: +39 335 246246
Fax: +39 55 588103
E-mail: a.quatraro@fol.it
History of use
Use of warning surfaces began in France in 1989, along rail transit platforms. French standard, NF P 98-351,1989, Footways—Provision for disabled persons—Warning for caution—Characteristic and testing of pedotactile warning devices for the blind and partially sighted, specifies textures, locations and placement of warning surfaces.
Along railway platforms
At crosswalks with cut curbs
At raised crosswalks.
Warning surfaces have been required since September 1999 on curb-ramps and on sidewalks where they adjoin raised crosswalks.
Specified texture
The texture of the domes is:
Dome height—5 mm
Dome base diameter—25 mm (domes not truncated)
Dome spacing—75 mm on center, with diagonal alignment.
The dome profile is specified by French standard NF P98-351. Figure 4-9 shows the dimensions of the dome.
Fig. 4-9. Dimensions of French dome profile (full dome, not truncated). Drawing shows fully rounded dome, 5 mm high and 25 mm in diameter.
Placement of warning surfaces
Depth of the warning surface and placement in relation to the street or platform edge are the same for different environments
Placed 900 mm back from platform edge or bottom of curb ramp, extending the length of the platform, or width of the curb ramp
420 mm deep
Materials
Commonly used materials are
Rubber
Concrete pavers
Methacrilate resin
Stainless steel tiles or stainless steel nails
The photograph in Figure 4-10 shows a detectable warning installation with steel nails manufactured by ACCESSIville.
Fig. 4-10. French detectable warning nails. Photo shows pavers with domed, steel nail heads forming the detectable warning surface along a blended curb.
Durability
Concrete pavers have performed best in France. Rubber is difficult to adhere. Methacrilate resin cracks and chips.
Acceptance
Warning surfaces are well accepted in France because of the involvement of persons with disabilities in their design. Surfaces were field tested and approved by persons with visual impairments and persons with mobility impairments. On rail transit platforms, all passengers tend to wait further from the platform edge, behind the warning.
Information provided by
Maryvonne Dejeammes CERTU9
Rue Juliette Recamier69456
Lyon 06France
Tel: (33)(0) 4 72 74 5867
Fax: (33)(0) 4 72 74 5930
E-mail: mdejam@certu.fr
History of use
Tactile ground surface indicators have been used in Germany since 1984. Warning and guidance surfaces are now in use in approximately 1000 (17%) of German railway stations, and they are widely used in pedestrian areas in towns and cities. Efforts toward standardization began in 1989. A sinusoidal wavy texture, in various dimensions, is used for guidance and warning.
Standard texture
Standards are to be published in April 2000 as DIN 32984. The texture [shown in an unnumbered figure] is comprised of parallel rounded grooves.
Grooves—3 mm deep
Spacing—10 to 20 mm on center
Location
TGSIs are used at curb ramps, medians, top and bottom of stair runs, transit platforms, and bus stops.
Fig. 4-11. Warning &guidance surface at German bus stop. Drawing shows bus stop with bus. There is a path of grooved paving on the sidewalk, extending the length of the bus, defining the waiting area. It appears to be set back from the curb at least two feet. A larger rectangle of the grooved pavers at one end of the path indicates the boarding area. A path of grooved paving extends from the waiting area back to the inner edge of the sidewalk, to alert pedestrians who are blind to the presence and location of the waiting area.
Products
The following products are used in Germany
Concrete tiles
Ceramic tiles
Hard rubber tiles
Metal plates
Maintenance and durability
Surfaces are easily cleaned using cleaning machines. Surfaces are less slippery than normal concrete surfaces when wet, oily or icy. Surfaces are adequately durable.
Acceptance
The guidance system is well accepted by all groups. Blind pedestrians who use a long cane find the guidance system helpful, but travel somewhat more slowly using the system than when not using it. Surfaces are well accepted by people with mobility impairments because they comply with a standard requiring a minimum tremor to wheels when crossing structured surfaces. Most rail passengers seem to use the guidance system as an indication of the limit of the safe waiting area on the platform. Older persons comment that their feet don’t get cold when they stand on rubber guidance tiles at bus stops.
Fig. 4-12. German TGSI path down a sidewalk and to a crosswalk. Photo is looking down a wide sidewalk of gray pavers along an urban street. A path of grooved pavers runs down the middle of the sidewalk. In the foreground it terminates in a larger, rectangular, "attention field," that alerts the pedestrian who is blind to an intersecting path leading to a crosswalk.
Information provided by
Gerhard Kuper
Von-Siemensstr. 6A
D 22880 Wedel, Germany
Phone & Fax: +49 4103-87083
E-mail: Gerhard.Kuper@arcormail.de
Volker Koenig
Wiedetwiete 42
D 22880 Wedel, Germany
Phone: +49 4103 84311
Fax: +49 4103 180438
History of use
Warning surfaces have been used in Austria since 1992, primarily on transit platforms. Approximately 80% of metro stations in Vienna have warning surfaces.
Specifications for warning textures ("attention fields")
&Omul;NORM V2102, adopted in 1997, specifies the dimensions of tactile indicators for warning (attention) and guidance, and the dimensions and placement for installations on transit platforms and on public rights-of-way. Warnings can be either truncated domes or truncated pyramids.
Height—5 mm preferred
4 mm minimum acceptable for exterior use
3 mm minimum acceptable for interior use
Dome diameter—base 30-40 mm; top 20-30 mm
Dome spacing—50-70 mm on center
Pyramid side—base 30 mm; top 20 mm
Pyramid spacing—45-50 mm on center, with parallel alignment
Warning and guidance indicators should contrast visually with adjoining
surfaces by at least 30%.
Placement and dimensions
&Omul;NORM V2102 also specifies dimensions and placement of warning textures to indicate changing situations and boarding locations on transit platforms and public rights-of-way. At changing situations, warning indicators should be 300-400 mm from a change such as a drop-off, stairs or a ramp; they should be 400-1000 mm deep. At boarding locations, warning indicators should be 100-120 cm square. At cut-through islands or medians, a 600 mm deep warning indicator should be placed at each side of the island. At raised crosswalks, warning indicators should be placed on the sidewalk 300-400 mm from the curb line.
Fig. 4-13. A linear directional surface leads to and beyond a level rail crossing. A detectable warning surface extends from building to curb line on both sides of tracks, Vienna, Austria. Photo shows a linear directional surface on a sidewalk, leading toward a level rail crossing. It is intersected by a detectable warning that extends from the building line to the curb. A similar arrangement of directional and warning surfaces can be seen on the far side of the tracks.
Fig. 4-14. A linear directional surface leads to a detectable warning surface at a curb, Vienna, Austria. Photo shows a linear directional surface intersecting a detectable warning at a curb ramp.
Materials
Materials used for warning indicators are:
Stone
Concrete
Road marking paint
Maintenance, durability and slip-resistance
Maintenance, durability and slip resistance of warning indicators are not a problem. Stone and concrete surfaces have not deteriorated. Road marking paint is in good condition after seven years. Snow and ice removal is not considered a problem. Warning surfaces are sometimes slippery, but only when surrounding surfaces are also slippery.
Acceptance
Warning indicators are well accepted. Pedestrians with visual impairments find them very helpful. There have been no complaints from persons with mobility impairments.
Information provided by
Günther ErtlWiener Linien-Vproj
A-1030 Wein, Erdbergstrasse 202
Vienna, Austria
Phone: +43 (0) 1 7909-41300
Fax: +43 (0) 1 7909 41390
E-mail: guenther.ertl@wienerlinien.co.at
History of use
In the early 1980s a rubber warning surface was introduced in Holland. Although detectability seemed good, the surface was not sufficiently durable. Extensive research has been conducted on 40 surfaces.
Recommended texture
A truncated dome ("blister") surface is now recommended for warning —25 domes in 30 x 30 cm module
Location
Warnings should be 60 cm deep, and as wide as the hazard. They are recommended for use in the following types of locations.
Dangerous crossings
All crossing points where there is no level difference between the pedestrian way and the vehicular way
Tops and bottoms of stairs
Bus stops
"Decision points" where tactile guidance surfaces intersect
Products
The product currently recommended is a metal plate that has been pre-formed with blisters, glued on 30 x 30 cm concrete, then coated with a gritty white or yellow epoxy layer.
Fig. 4-15. Detectable warning pavers at a blended curb. Photo shows a 2 ft deep truncated dome detectable warning, placed about 1 ft back from the street, along a blended curb at a mid-block crossing.
Information provided by
Henk Grotendorst, Dutch Federation of the Blind and Partially Sighted
Postbus 2062
3500 GB Utrecht, Netherlands
Phone: +30 299 28 78
E-mail: h.grotendorst@sb-belang.nl
International Organization for Standardization (ISO)
ISO is a worldwide federation of national standards bodies. International Standards are prepared through the work of ISO technical committees and working groups. International organizations, governmental and non-governmental, in liaison with ISO, participate on technical committees and working groups. Adoption of ISO standards by member countries is voluntary.
Technical Committee 173(ISO/TC173)
ISO/TC173--Technical systems and aids for disabled or handicapped persons, has a number of working groups, including one on tactile ground/floor surface indicators (TGSIs). Working Group 7 completed Committee Draft ISO/CD 11550.2(E), Technical aids for blind and vision impaired persons, "Tactile ground/floor surface indicators (TGSIs)," in November 1999.
ISO draft on TGSIs
The ISO draft on TGSIs specifies requirements for design and installation of tactile indicators for use on ground or floor surfaces to assist the orientation and mobility of people with visual impairments. It includes specifications for warning, directional, and shared pedestrian/cycle surface indicators
Warning surface: The warning surface is comprised of truncated domes:
Dome height- 5 ± .5 mm
Dome top diameter- 12-25 mm
Dome spacing- 50-65 mm on
Directional surface: The directional surface is a series of raised elongated bars running in the direction of pedestrian travel.
Bar height- 5 ± .5 mm
Bar top width- 30 ± .5 mm
Bar spacing- 75 ± .5 mm on center
Shared pedestrian/bicycle indicator
The shared pedestrian/bicycle indicator is
a central delineator strip with a trapezoidal profile, 150 ± 1 mm wide
Trapezoid height: 12-20 mm ± 1 mm
Top surface: 50 ± .1 mm
Contrast luminance factor
Recommended minimum of 30% luminance contrast between tactile indicators and surrounding surfaces
Applications: Applications for warning surfaces are:
Curb-ramps
Crossings where there is a raised road surface
Vehicle crossovers with high traffic flows
Pedestrian refuges/medians
Railway platforms and passenger wharves
Level railway crossings
Stairways and moving stairs
Intersections with shared pedestrian/bicycle traffic
Shared pedestrian/bicycle paths.
Installation of warning surfaces
Warning surfaces are to be:
Installed across the full width of the trafficable surface
Installed perpendicular to the path of travel
Set back a maximum of 400 mm from the hazard
Have a minimum depth of 400 mm (600 mm preferred)
Have a base surface level 0-3 mm above the surrounding surface
Laid so there is no likelihood of surfaces lifting
Have slip resistance in accordance with the standard of the country where the application is laid
U.S. USE OF DETECTABLE WARNING SURFACES: CASE STUDIES
Summary
This chapter includes information on use of truncated dome detectable warnings in the U.S. The method of obtaining information is described, and a summary of the information is given. The chapter concludes with case studies of selected cities and rail transit systems where truncated dome detectable warnings have been installed. Case studies include history, locations, maintenance and durability, and acceptance of detectable warnings in each location.
Chapter contents
This chapter covers the following topics:
Locating U.S. installations of detectable warning surfaces / 52
Responses to mail survey / 52
Interviews regarding detectable warning installations / 53
Interview locations / 53
Interview questions / 54
Interview results - general; installation problems; maintenance; durability; public reaction / 55
Austin, TX / 59
Metropolitan Atlanta Rapid Transit Authority (MARTA), Atlanta, GA / 61
Roseville, CA / 62
Metro North Railroad, greater New York City / 63
Harrisburg, PA / 65
Massachusetts Bay Transportation Authority (MBTA), Boston, MA / 66
Cleveland, OH / 67
Baltimore County, MD / 68
Bay Area Rapid Transit (BART), San Francisco, CA / 69
Claremont, CA / 70
LOCATING U.S. INSTALLATIONS OF DETECTABLE WARNING SURFACES
Developing a list of locations
An E-mail survey was sent to several mailing lists of individuals who might have information regarding locations of detectable warnings surfaces in the United States. Manufacturers were also contacted and installation locations were requested. Available pedestrian design guidelines were also reviewed to determine locations that currently require a truncated dome detectable warning surface.
Mail survey
In October 1999, a survey was sent to E-mail listserves whose subscribers might be aware of locations where a texture change is used to provide information to pedestrians who are visually impaired or blind. Groups included pedestrian advocates, orientation and mobility specialists, Association for Education and Rehabilitation of the Blind and Visually Impaired (AER), individuals who are blind or visually impaired, and traffic engineers.
The survey requested specific locations, types of location (curb ramp, transit platform, edge of street, medians) and the texture (grooves, grid pattern, brick, rubber mat, truncated domes, or other), of any texture change intended to provide information to pedestrians with visual impairments. The survey also requested the name of a contact person who might be able to answer questions about experience with truncated dome detectable warning surfaces.
Other information sources
Manufacturers of truncated dome detectable warning materials, who were asked for contacts in locations where their products had been installed
Conversations with Access Board staff
A review of references in previously published materials
Personal contacts of authors
American Public Transit Association
Responses to survey
The 48 responses included surveys from 28 states, the District of Columbia and Canada. Many respondents noted two or more locations and types of locations, for example, the name of an entire transit system that had detectable warnings and a list of several intersections in that city with grooves on the curb-ramps. Five respondents replied that they were not aware of any locations where a texture change was used. Thirty-nine reported the use of other surfaces besides, or in addition to, truncated domes, including grooves, grid patterns, standard bricks, exposed aggregate, and "exposed rock."
State and local requirements
Responses from several states indicated that there were state or local requirements for tactile surfaces on curb-ramps. For example, a traffic engineer from Minnesota stated that an exposed aggregate was required on all curb-ramps, and a response from Phoenix stated that grooves were required on curb-ramps in all new construction.
California requires grooves at the top of the curb ramp and detectable warnings where the slope is less than 1:15.
Fig. 5-1. A minimally detectable warning surface in Portland, ME. Photo shows a wide brick curb ramp that has five rows of cobblestones at the bottom, parallel to the curb line.
INTERVIEWS REGARDING DETECTABLE WARNING INSTALLATIONS
Interview
Research assistants made calls to locations identified by the initial survey as having truncated dome detectable warnings. The detectable warning and its location was confirmed and it was determined that the individual being interviewed had some responsibility related to its installation or use. Names of additional contacts were requested.
Locating appropriate persons
Architects and facilities maintenance supervisors of transit systems, ADA coordinators of transit systems and cities, traffic engineers, city engineers, and various public works officials were queried. Phone calls were made to city public works departments, engineering departments, and transit systems in order to locate knowledgeable individuals. Some cities have a designated curb ramp manager- many do not. In several situations, the public official was unaware of the presence of detectable warning within his/her jurisdiction until the researcher identified the specific location.
Types of locations for detectable warnings
The people interviewed reported the following types of locations for detectable warnings:
Curb-ramps at intersections- 18 jurisdictions
Curb-ramps throughout the city- 2 cities
Entrances to public stores, between parking lot and entrance- 4 jurisdictions. Transit system platforms, or light rail loading areas, usually at numerous locations throughout systems- 17 systems
Raised intersection crosswalks, along driveways at a school for the blind, and a university- 3 reports
Fig. 5-2. Curb ramp with exposed aggregate surface in Virginia. Pedestrians who are blind do not reliably detect exposed aggregate concrete. Photo shows 4’ wide curb ramp of exposed aggregate. The aggregate looks very coarse.
City interviews
Interviews were conducted for these cities:
Roseville, CA
Sacramento, CA
San Diego, CA
San Francisco, CA
Chicago, IL
Cambridge, MA
Towson, MD
Anoka, MN
Greensboro, NC
Lakeland, FL
Transit system Interviews
Interviews were conducted for these transit systems:
San Diego Trolley, San Diego, CA
Bay Area Rapid Transit, (BART), San Francisco, CA
San Francisco Municipal Rail-way (MUNI), San Francisco, CA
Valley Transportation Authority, San Jose, CA
AC Transit, San Pablo, CA
Metrolink, Southern California Commuter Rail
Sacramento Regional Transit, Sacramento, CA
Metro-Dade Transit, Miami, FL
Metropolitan Atlanta Rapid Transit Authority (MARTA), Atlanta, GA
Chicago Transit Authority, Chicago, IL
MTA and Maryland Area Rail Commuter (MARC), Baltimore, MD
Massachusetts Bay Transportation Authority, Boston, MA
Metro North Railroad, Greater New York City, NY
Cleveland Regional Transit Authority, Cleveland, OH
Portland TriMet, Portland, OR
Virginia Railway Express, Washington DC & VA
Other interviews
Interviews were conducted with these individuals and organizations:
Maintenance supervisor at University of Alaska, Fairbanks, AK
Maintenance supervisor at ARCO, Anchorage, AK
Blind person in Canada
Manager at a TOYS R US store, Roseville, CA
Manager of Checkers Drive-In, Lakeland, FL
Contractor in Atlanta, GA
Blind person in Towson, MD
Consultant in accessibility issues, Ottawa, ON, Canada
Employee of Q-Lube, Bonney Lake, WA
Maintenance supervisor at the Washington State School for the Blind, Seattle, WA
Contractor in Ontario, CA