Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments
Final Report
(Task Order 18 under Project DTFH61-01-C-00049) Authors: James Jenness & Jeremiah Singer May 24, 2006 Prepared for: Federal Highway Administration Washington, DC Prepared by: Westat Rockville, Maryland Visual Detection of Detectable Warnings Table of Contents
Executive Summary ....................................................................................................................................1 1 Introduction.........................................................................................................................................4 1.1 Objectives........................................................................................................................4 1.2 Background .....................................................................................................................4 1.3 Previous Research ...........................................................................................................5 1.3.1 Need for Detectable Warnings at Curb Ramps ...................................................5 1.3.2 Detectable Warnings May Provide Visual Guidance..........................................5 1.3.3 Visual Detection of Detectable Warning Surfaces..............................................6
2 Method .................................................................................................................................................7 1.4 1.5 1.6 1.7 Participants......................................................................................................................7 Materials........................................................................................................................10 Testing Site and Conditions ..........................................................................................14 Procedure ......................................................................................................................15 1.7.1 Introduction and Vision Testing .......................................................................15 1.7.2 Visual Detection Distance.................................................................................16 1.7.3 Color Naming, Conspicuity Rating, and Other Comments ..............................16 Participants' Vision.......................................................................................................17 Lighting Conditions ......................................................................................................18 Visual Detection............................................................................................................19 False Detections ............................................................................................................20 Visual Detection Distance.............................................................................................21 2.5.1 Comparing Visual Detection Distances for Detectable Warnings....................29 Conspicuity Ratings ......................................................................................................35 2.6.1 Comparing Conspicuity Ratings for Detectable Warnings...............................42 Comparing Visual Detection Rates and High Conspicuity Ratings for Detectable Warnings ......................................................................................................................47 Effects of Luminance Contrast on Visual Detection and Conspicuity of Detectable Warnings ......................................................................................................................52 Models to Predict Visual Detection and High Conspicuity Ratings .............................57 Other Factors that May Predict Visual Detection and High Conspicuity Ratings........57 Perceived Color of Detectable Warnings......................................................................60 Comments from Participants.........................................................................................61 2 Results................................................................................................................................................17 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12
3 Discussion ..........................................................................................................................................62 3.1 Key Findings .................................................................................................................62 3.2 Study Limitations and Other Issues ..............................................................................63 3.3 Guidance on the Visual Properties of Detectable Warnings.........................................65
Appendix A: Pedestrians with Visual Impairments...............................................................................67 Appendix B: Overview of Federal Regulations and Guidance for Detectable Warnings...................74 ii Visual Detection of Detectable Warnings Appendix C: Previous Research on the Visibility of Detectable Warning Surfaces ...........................77 Appendix D: Photometric Measurements ...............................................................................................83 Appendix E: Vision Tests..........................................................................................................................87 Appendix F: Color Names Used by Participants to Describe Detectable Warnings ...........................88 Appendix G: Comments from Participants ............................................................................................94 References ................................................................................................................................................105 iii Visual Detection of Detectable Warnings List of Figures
Figure 1. Chart. Distribution of Participants' Ages by Gender ..................................................... 9 Figure 2. Photo. Uniformly Colored Detectable Warnings (Color Samples) .............................. 11 Figure 3. Photo. Black-and-white Patterned Detectable Warnings ............................................. 12 Figure 4. Diagram. Schematic View of Testing Site ................................................................... 15 Figure 5. Chart. Distribution of Participants' Visual Acuity ....................................................... 17 Figure 6. Chart. Distribution of Participants' Contrast Sensitivity Measured With the PelliRobson Chart................................................................................................................ 18 Figure 7. Graph. Horizontal Illuminance (Mean and Standard Deviation) for Each Participant's Trials by the Estimated Percent Cloud Cover During the Testing Session ......................................................................................................................... 19 Figure 8. Graph. White Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance.......................................................................... 23 Figure 9. Graph. Light Gray Detectable Warning: Percentage of Participants Who Could See The Detectable Warning at Each Distance............................................................ 23 Figure 10. Graph. White Concrete Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance .................................................. 24 Figure 11. Graph. Brown Concrete Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance .................................................. 25 Figure 12. Graph. Dark Gray Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ............................................................. 25 Figure 13. Graph. Federal Yellow Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance .................................................. 26 Figure 14. Graph. Pale Yellow Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ............................................................. 26 Figure 15. Graph. Bright Red Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ............................................................. 27 Figure 16. Graph. Orange-Red Detectable Warning: Percentage of Participants Who Could See The Detectable Warning at Each Distance............................................................ 27 Figure 17. Graph. Black Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance.................................................................... 28 Figure 18. Graph. Black with White Border Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ......................................... 28 Figure 19. Graph. Black-and-White Stripes Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ......................................... 29 Figure 20. Graph. White with Black Border Detectable Warning: Percentage of Participants Who Could See the Detectable Warning at Each Distance ......................................... 29 Figure 21. Chart. White Detectable Warning: Conspicuity Ratings by Sidewalk Type.............. 35 Figure 22. Chart. Light Gray Detectable Warning: Conspicuity Ratings by Sidewalk Type...... 36 Figure 23. Chart. White Concrete Detectable Warning: Conspicuity Ratings by Sidewalk Type ............................................................................................................................. 36 Figure 24. Chart. Brown Concrete Detectable Warning: Conspicuity Ratings by Sidewalk Type ............................................................................................................................. 37 Figure 25. Chart. Dark Gray Detectable Warning: Conspicuity Ratings by Sidewalk Type ...... 37 iv Visual Detection of Detectable Warnings Figure 26. Chart. Federal Yellow Detectable Warning: Conspicuity Ratings by Sidewalk Type ............................................................................................................................. 38 Figure 27. Chart. Pale Yellow Detectable Warning: Conspicuity Ratings by Sidewalk Type.... 38 Figure 28. Chart. Bright Red Detectable Warning: Conspicuity Ratings by Sidewalk Type...... 39 Figure 29. Chart. Orange-Red Detectable Warning: Conspicuity Ratings by Sidewalk Type..... 39 Figure 30. Chart. Black Detectable Warning: Conspicuity Ratings by Sidewalk Type .............. 40 Figure 31. Chart. Black with White Border Detectable Warning: Conspicuity Ratings by Sidewalk Type.............................................................................................................. 40 Figure 32. Chart. Black-and-White Stripes Detectable Warning: Conspicuity Ratings by Sidewalk Type.............................................................................................................. 41 Figure 33. Chart. White with Black Border Detectable Warning: Conspicuity Ratings by Sidewalk Type.............................................................................................................. 41 Figure 34. Chart. Brick Sidewalk: Percent of Participants Who Saw Each Detectable Warning and Percent Who Rated It Highly Conspicuous............................................ 48 Figure 35. Chart. Asphalt Sidewalk: Percent of Participants Who Saw Each Detectable Warning and Percent Who Rated It Highly Conspicuous............................................ 49 Figure 36. Chart. White Concrete Sidewalk: Percent of Participants Who Saw Each Detectable Warning and Percent Who Rated It Highly Conspicuous.......................... 50 Figure 37. Chart. Brown Concrete Sidewalk: Percent of Participants Who Saw Each Detectable Warning and Percent Who Rated It Highly Conspicuous.......................... 51 Figure 38. Chart. Data Combined Across All Four Sidewalk Types Tested: Percent of All Trials Where the Participant Saw the Detectable Warning and Percent of All Trials Where the Detectable Warning Was Rated Highly Conspicuous...................... 52 Figure 39. Graph. Percentage of Study Participants (n = 50) Who Could See the Detectable Warning by Luminance Contrast (Linear Models) ...................................................... 54 Figure 40. Graph. Percentage of Study Participants (n = 50) Who Could See the Detectable Warning by Luminance Contrast (Logarithmic Models)............................................. 55 Figure 41. Graph. Percentage of Participants Who Rated Detectable Warnings Highly Conspicuous (Rating of 4 or 5) by Luminance Contrast.............................................. 56 v Visual Detection of Detectable Warnings List of Tables
Table 1. Self-reported Use of Travel Aids.................................................................................... 10 Table 2. Self-reported Medical Conditions Affecting Vision....................................................... 10 Table 3. Chromaticity and Reflectance of Materials .................................................................... 14 Table 4. Percentage of Participants (n = 50) Who Saw Each Detectable Warning at 2.4 m (8 ft) and 7.9 m (26 ft) for Each Sidewalk Type.............................................................. 20 Table 5. Some 95-Percent Confidence Intervals For Percentages Shown in Figure 8 Through Figure 20 ....................................................................................................................... 22 Table 6. Brick Sidewalk: Significant Differences in Visual Detection Distance for Detectable Warnings..................................................................................................... 31 Table 7. Asphalt Sidewalk: Significant Differences in Visual Detection Distance for Detectable Warnings..................................................................................................... 32 Table 8. White Concrete Sidewalk: Significant Differences in Visual Detection Distance for Detectable Warnings..................................................................................................... 33 Table 9. Brown Concrete Sidewalk: Significant Differences in Visual Detection Distance for Detectable Warnings..................................................................................................... 34 Table 10. Brick Sidewalk: Significant Differences in Conspicuity Ratings for Detectable Warnings ....................................................................................................................... 43 Table 11. Asphalt Sidewalk: Significant Differences in Conspicuity Ratings for Detectable Warnings ....................................................................................................................... 44 Table 12. White Concrete Sidewalk: Significant Differences in Conspicuity Ratings for Detectable Warnings..................................................................................................... 45 Table 13. Brown Concrete Sidewalk: Significant Differences in Conspicuity Ratings for Detectable Warnings..................................................................................................... 46 Table 14. Percentage of Participants (n = 50) Who Rated Conspicuity High (4 or 5) for Each Detectable Warning and Sidewalk Pairing ................................................................... 47 Table 15. Reflectance Factors (R) and Percent Luminance Contrast of Detectable Warnings on Four Sidewalk Types ............................................................................................... 53 Table 16. Results from Fitting a Logistic Regression Model to Predict Probability of Visual Detection at 2.44 m (8 ft).............................................................................................. 59 Table 17. Results from Fitting a Logistic Regression Model to Predict Probability of Visual Detection at 7.92 m (26 ft)............................................................................................ 59 Table 18. Results from Fitting a Logistic Regression Model to Predict Probability of a High Conspicuity Rating (4 or 5) .......................................................................................... 60 vi Visual Detection of Detectable Warnings Executive Summary
Detectable warnings are walking surfaces that are primarily intended to provide a tactile cue to pedestrians who are visually impaired. They are installed at locations such as the edge of a train platform or at the transition between the sidewalk and the street to warn pedestrians of the potential hazard that lies ahead. The tactile properties of detectable warnings result from a grid of small, truncated (flat-topped) domes across the warning surface. This pattern has been standardized by the U.S. Access Board and testing has shown that the pattern can be detected underfoot or by cane without causing a tripping hazard or obstructing wheelchairs. Despite the proven tactile benefits of detectable warnings, little research has been conducted to evaluate the visual detectability of various detectable warning materials. Detectable warnings that provide salient visual cues in addition to tactile cues may help many pedestrians with visual impairments to locate hazards or curb ramps from a greater distance than is possible using the tactile cues alone. Some pedestrians may use them to orient to a curb cut or ramp at the end of a crosswalk. The objectives of this study were (1) to determine which detectable warning colors and patterns are visually detectable and conspicuous to pedestrians with visual impairments and (2) to provide recommendations related to color, pattern, and luminance contrast of detectable warnings for placement on sidewalks. Fifty men and women ranging in age from 24 to 92 participated in this study. All participants had impaired but useful vision. Most were legally blind. All participants reported they had difficulty locating the boundary between sidewalks and streets. Thirteen detectable warnings were tested. The set included ten uniform colors (white, simulated white concrete, simulated brown concrete, light gray, dark gray, bright federal yellow, pale yellow, bright red, orange-red, and black) and three black-and-white patterns. Each detectable warning was a .91 m (3 ft) wide by .61 m (2 ft) long composite panel designed for surface application. Participants viewed each detectable warning on four different horizontal backgrounds. Each background was 1.22 m (4 ft) wide by 2.44 m (8 ft) long and was constructed to simulate the appearance of a red brick sidewalk, a dark gray asphalt sidewalk, a white concrete sidewalk, and a brown concrete sidewalk. The study was conducted during midday hours with dry surfaces. Participants viewed each combination of detectable warning and sidewalk individually. To determine detection distance, participants first viewed the sidewalk from 7.92 m (26 ft) away and, if they could not see the detectable warning from this distance, they began to walk closer until they were confident that a detectable warning was present. On some trials there was no detectable warning present. Once detectable distance had been measured, participants were asked to view the detectable warning from a distance of 2.44 m (8 ft) and to describe the color and/or pattern of the detectable warning. Finally, participants were asked to rate the conspicuity (attention-getting property) of the detectable warning on a five-point scale. 1 Visual Detection of Detectable Warnings Participants viewed each combination of detectable warning and background color individually. To determine detection distance, participants first viewed the simulated sidewalk section from 7.92 m (26 ft) away and if they could not see the detectable warning from this distance, they began to walk closer until they were confident that a detectable warning was present. On some trials there was no detectable warning present. After detection distance had been measured, participants viewed the detectable warning from a distance of 2.44 m (8 ft) and described its color, and rated the conspicuity (attention-getting property) of the detectable warning on a five-point scale. Detection distance results indicate that pedestrians with visual impairments were able to see most combinations of detectable warning and sidewalk from 2.44 m (8 ft) away, but were less likely to see them from 7.92 m (26 ft) away. Detectable warnings that were similar in color to the sidewalk were seen by few participants, indicating that visual cues provided by the truncated dome pattern itself are not sufficient to ensure visual detection. The color of the sidewalk strongly influenced how easily single-color detectable warnings could be seen; however, black-and-white patterned detectable warnings were visually detectable and conspicuous for most participants across all sidewalk types. The luminance contrast provided by the detectable warning and the sidewalk (or by the patterns) was an important factor for predicting the likelihood that a detectable warning would be seen. Where luminance contrast was 70 percent or greater, about 95 percent of participants were able to see the detectable warning from 2.44 m (8 ft) away. Detectable warnings that provided at least 60 percent contrast could be seen by about 92 percent of participants from 2.44 m (8 ft) away. Dark detectable warnings on a dark sidewalk were an exception. Although providing moderately high luminance contrast, these combinations were detected less often than would be predicted from their luminance contrast. Detection distance results indicate that pedestrians with visual impairments were able to see most combinations of detectable warning and sidewalk from 2.44 m (8 ft) away, but were less likely to see them from 7.92 m (26 ft) away. Detectable warnings that were similar in color to the sidewalk were seen by few participants, indicating that visual cues provided by the truncated dome pattern itself are not sufficient to ensure visual detection. The color of the sidewalk strongly influenced how easily single-color detectable warnings could be seen, however, black-and-white patterned detectable warnings were visually detectable and conspicuous for most participants on all sidewalk colors tested. The luminance contrast provided by the detectable warning and the sidewalk (or by the patterns) was an important factor for predicting the likelihood that a detectable warning would be seen. Where luminance contrast was 70 percent or greater, about 95 percent of participants were able to see the detectable warning from 2.44 m (8 ft) away. Detectable warnings that provided at least 60 percent contrast could be seen by about 92 percent of participants from 2.44 m (8 ft) away. Dark detectable warnings on a dark sidewalk were an exception. Although providing moderately high luminance contrast, these combinations were detected less often than would be predicted from their luminance contrast. For dark single-color detectable warnings and black-and-white patterned detectable warnings a few participants commented that the detectable warning looked like something else (e.g. hole, metal grate). 2 Visual Detection of Detectable Warnings Besides luminance contrast, regression analyses indicated that some other characteristics of detectable warnings were generally associated with high detection rates and high conspicuity ratings. These include color (reds and yellows rather than achromatic) and reflectance (lighter colors rather than darker colors). For the range of conditions tested, neither illumination level (per trial) nor sky conditions (percent cloud cover per session) affected detection and conspicuity of detectable warnings. Based on the results of the study, the authors recommend the following: · · · · Do not use detectable warnings that are the same color as the sidewalk. Select detectable warning color based on the sidewalk color to provide high luminance contrast either light-on-dark or dark-on-light. Avoid using combinations of sidewalk and detectable warning materials where both surfaces are dark (reflectance less than 10 percent). If a contrast-based requirement for detectable warnings installations is used, the guidance should include both a minimum luminance contrast and a minimum reflectance for the lighter of the two surfaces providing the contrast. If a standardized color scheme is desired for detectable warnings, adopt a twocolor large pattern which provides high internal contrast to ensure high conspicuity across all sidewalk types. If a standardized color scheme is desired for single-color detectable warnings, federal yellow may be a good choice. It provides a high level of conspicuity for a given level of luminance contrast. In this study reds and yellows generally provided higher conspicuity than achromatic colors. If a small set of standardized colors is desired for detectable warnings on different sidewalk types then federal yellow may be a good choice where adjacent walking surfaces are dark. A dark brick red color (orange-red) may be a good choice where adjacent walking surfaces are light. Consider how visual contrast between the detectable warning and sidewalk surfaces may change over time as the materials age. · · · · Further visibility testing of detectable warnings should include a broader range of lighting conditions (dusk, dawn, artificial illumination), determination of optimal internal contrast patterns for two-color detectable warnings, and viewing detectable warnings in naturalistic roadway environments with unpredictable crossing locations, distractions, visual obstructions, wet surfaces, and so forth. Further research also should include pedestrians' perceptions of different detectable warning colors (e.g. Is the detectable warning recognized as being safe to step on? Does the detectable warning convey the intended message?). 3 Visual Detection of Detectable Warnings 1 Introduction
1.1 Objectives
The primary objectives of this project are to determine whether various detectable warning materials are visually detectable by pedestrians who have visual impairments and to provide recommendations related to color and luminance contrast of detectable warnings. 1.2 Background
Detectable warning surfaces are intended primarily to provide a tactile cue to pedestrians who are blind or have visual impairments. Major causes of visual impairments in the United States are described briefly in Appendix A. The majority (80%) of people who are legally blind retain some degree of visual function, 1 and these people, along with pedestrians who have less severe visual impairments, may benefit from detectable warnings, which are both visually and tactilely distinctive. The tactile properties of detectable warning surfaces result from a grid pattern of raised, flat-topped, truncated domes that can be felt underfoot or detected by a long cane or a wheelchair without causing a tripping hazard. The size and spacing of the truncated domes have been clearly specified by the U.S. Access Board. 2 3 However, guidance concerning the visual properties of detectable warning surfaces is much less specific. The U.S. Access Board states that "Detectable warning surfaces shall contrast visually with adjoining surfaces, either light-on-dark or dark-on-light." 4 The Public Rights-ofWay Access Advisory Committee has previously noted that there is a lack of human factors research with vision-impaired pedestrians.5 There is not a sufficient quantitative research basis to support any more specific guidance with respect to the visual properties of detectable warning surfaces, particularly color and contrast. An overview of Federal rule making and guidance on detectable warnings is given in Appendix B. In this report, the terms "detectable warning" and "detectable warning surface" refer to the standard truncated dome surfaces described in the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and described by the U.S. Access Board. 6 7 8 9 10
American Foundation for the Blind, "Glossary of Eye Conditions," 2004. Retrieved December 9, 2004, from the American Foundation for the Blind website: http://www.afb.org/Section.asp?DocumentID=2139. 2 U.S. Access Board, Draft Guidelines for Accessible Public Rights-of-Way (Washington, DC: 2002). Retrieved January 3, 2005, from the U.S. Access Board website: http://access-board.gov/rowdraft.htm. 3 Draft Public Rights-of-Way Accessibility Guidelines, U.S. Access Board (Washington, DC: 2005). Retrieved December 1, 2005 from the U.S. Access Board website: http://www.accessboard.gov/prowac/draft.htm. 4 Ibid. 5 Public Rights-of-Way Access Advisory Committee, U.S. Access Board, Building a True Community (Washington, DC: 2001). 6 U.S. Access Board, Americans with Disabilities Act (ADA) Accessibility Guidelines for Buildings And Facilities (Washington, DC: 1991). Retrieved January 3, 2005, from the U.S. Access Board website: http://www.access-board.gov/adaag/ADAAG.pdf. 7 U.S. Access Board, Draft Guidelines for Accessible Public Rights-of-Way (Washington, DC: 2002). Retrieved January 3, 2005, from the U.S. Access Board website: http://access-board.gov/rowdraft.htm.
1 4 Visual Detection of Detectable Warnings Note that detectable warnings with truncated domes as used in the U.S. are only one of several types of tactile patterns used through the world as detectable warnings, and represent only a subset of the types of Tactile Ground Surface Indicators (TGSIs) that are being used as a navigational aid for pedestrians who are visually impaired. For example, various tactile pavements have been used in Japan since the 1960s, and in England there are currently seven different types of tactile paving patterns used. 11 12 13 Persons interested in the practices of other countries may wish to consult Detectable Warnings: Synthesis of U.S. and International Practice, which is available from the U.S. Access Board. 14 1.3 Previous Research
1.3.1 Need for Detectable Warnings at Curb Ramps
For pedestrians who have visual impairments, curbs used to be a reliable cue for detecting the boundary between the sidewalk and a street. However, now that curb ramps and other flush transitions are used at crosswalks to improve the accessibility of sidewalks for people who cannot negotiate curbs, the curb edge has become a less reliable navigational cue for many pedestrians. This is especially relevant for blind pedestrians traveling in unfamiliar areas. Bentzen and Barlow (1995) reported that blind pedestrians using a long cane failed to detect the edge of an intersecting street on 39% of 557 approaches to unfamiliar intersections, and that shallower ramps were more difficult to detect than steeper ramps. For curb ramps encountered with slopes of 4 degrees (1:14) or less, there was a 51% rate of entering the street rather than stopping on the sidewalk or ramp. 1.3.2 Detectable Warnings May Provide Visual Guidance
Pedestrians who are visually challenged often have difficulty locating crosswalks, properly aligning themselves to cross, determining when it is safe to cross, maintaining a straight path while crossing, and completing their crossing before perpendicular traffic
U.S. Access Board, ADAAG Requirements for Detectable Warnings, (Washington, DC: 2003). Retrieved December 28, 2004, from the U.S. Access Board website: http://accessboard.gov/adaag/dws/update.htm. 9 U.S. Access Board, Revised ADA and ABA Accessibility Guidelines (Washington, DC: 2004). Retrieved January 3, 2005, from the U.S. Access Board website: http://www.access-board.gov/ada-aba/final.pdf. 10 U.S. Access Board, Draft Public Rights-of-Way Accessibility Guidelines (Washington, DC: 2005). Retrieved December 1, 2005, from the U.S. Access Board website: http://www.accessboard.gov/prowac/draft.htm. 11 Department for Transport, Guidance on The Use Of Tactile Paving Surfaces (London, UK: 1999). Retrieved October 5, 2004, from Department for Transport website: http://www.dft.gov.uk/stellent/groups/dft_mobility/documents/pdf/dft_mobility_pdf_503283.pdf. 12 Department for Transport, Inclusive Mobility: A Guide To Best Practice on Access to Pedestrian and Transport Infrastructure, (London, UK: 2002). Retrieved October 5, 2004, from Department for Transport website: http://www.dft.gov.uk/stellent/groups/ dft_mobility/documents/pdf/dft_mobility_pdf_503282.pdf. 13 Dowson, A.J., "The Development of Surface Tactile Indicators," Proceedings of the 7th International Conference on Concrete Block Paving (London, UK: 2003). Sun City, South Africa. Retrieved October 5, 2004, from Interpave website: http://www.paving.org.uk/pdf/036.pdf. 14 Bentzen, B.L., Barlow, J.M., & Tabor, L.S., U.S. Access Board, Detectable Warnings: Synthesis of U.S. and International Practice (Washington, DC: 2000).
8 5 Visual Detection of Detectable Warnings approaches. 15 For pedestrians who have some functional vision, detectable warnings that can be seen before they are detected by cane or under foot may provide useful information: · · · · To provide a visual cue to identify the presence of a hazard (intersection between walkway and street). To function like a stop sign and direct appropriate behavior by warning pedestrians to stop and determine the nature of the hazard before proceeding. To provide a visual cue for locating the curb ramp (and crosswalk). The detectable warning is usually a useful point of departure for crossing the street. To provide a visual cue for orienting away from the departure curb, by aligning perpendicular to the detectable warning edge. This may be especially useful where the orientation of the curb-roadway boundary is difficult to detect, however, this cue is somewhat unreliable. Depending on the geometry of the street and crosswalk the detectable warning may not be installed at an angle perpendicular to the crosswalk. To provide a visual cue for the destination on the opposite side of the street. The detectable warning may serve as a visual cue to guide pedestrians to the destination curb ramp, helping them to maintain a proper travel path while crossing. · 1.3.3 Visual Detection of Detectable Warning Surfaces
A search of the literature found reports on installation and durability of detectable warning surfaces (e.g., Ketola & Chia, 1994; Kaplan, 2004) and some studies that have evaluated detectable warning surfaces for detection under foot or by long cane (e.g., Peck & Bentzen, 1987; Bentzen, Nolin, Easton, Desmarais, & Mitchell, 1994; Tijerina, Jackson, & Tornow, 1994, 1995). In general, the participants selected for these detection studies have had little or no functional vision (usually light perception only) so that tactile and auditory detection could be evaluated without having the results confounded by visual detection. Only five reports were found which included visual assessments of detectable warning surfaces by people with visual impairments (Templer, Wineman, & Zimring, 1982; Bentzen, Nolin, & Easton, 1994; O'Leary, Lockwood, & Taylor, 1996; Bentzen & Myers, 1997; Kemp, 2003). Each of these reports is described in detail in Appendix C. These studies varied widely in terms of the number of participants, types and number of detectable warning materials tested, procedures used, and the amount of detail provided in the report. Participants in these studies generally were recruited based on self reported visual ability. Three of the studies used six or fewer participants, and the other two
Bentzen. B.L., Barlow, J.M., & Bond, T., "Pedestrians Who Are Blind at Unfamiliar Signalized Intersections: Research on Safety," Proceedings of the Transportation Research Board 2004 Annual Meeting (Washington, DC: 2004).
15 6 Visual Detection of Detectable Warnings studies had 24 and 27 participants. One of these was conducted outdoors under natural illumination, and the other was conducted indoors under artificial illumination. The size of the detectable warnings used varied widely between studies. Most of the studies reviewed do not adequately report on the lighting conditions and color and luminance contrast between detectable warning surfaces and surrounding surfaces. Clearly, some of the studies were meant only to be informal assessments of particular products rather than scientifically rigorous experiments. Overall, yellow detectable warning surfaces (particularly federal yellow, also known as safety yellow) have been found to be highly visually detectable and, as expected, higher contrasts between the warning surface and the adjacent surface are more detectable than lower contrasts. Participants have generally rated federal yellow warning surfaces as being highly detectable. Although dark-on-light contrast pairs have not been tested as often as light-on-dark contrast pairs, there is some indication that they may be just as effective. Finally, there is some evidence that low reflectance of the lighter surface in a contrast pair may reduce visibility, even when luminance contrast is moderately high. 2 Method Systematic outdoor evaluations were performed on 13 different detectable warning colors/patterns on 4 different simulated sidewalk surfaces by 50 visually impaired participants who have visual impairments. The two main dependent measures were: 1. Whether the detectable warnings could be seen from distances between 2.44 m (8 ft) and 7.92 m (26 ft). 2. Participants' subjective ratings of the likelihood that the detectable warnings would attract their attention (conspicuity). 1.4 Participants
Fifty adults with low vision were recruited through contacts with local organizations for people who are blind or visually impaired. Information about the study was also distributed through email lists, flyers in medical offices and retirement communities, and through personal contacts of orientation and mobility specialists in the Washington, DC, area. Some participants were referred by other participants. Individuals were invited to participate based on their responses to a screener questionnaire. When people called to inquire about the study they were asked about the nature and severity of their visual impairments, their frequency of travel and difficulties experienced while walking, and the travel aids they use. Self-reported difficulty in detecting streets and curb ramps was a major criterion used to select participants for the study. Participants were compensated with $75 for their time and were reimbursed for local travel expenses. Participants ranged in age from 24 to 92 years old, with a median age of 54. The distribution of participants' ages by gender is shown in Figure 1. There were 31 women and 19 men in the sample. Each age group contained both men and women except for the 7 Visual Detection of Detectable Warnings youngest age group (20 ­ 29 years) and oldest age group (90-99) which each consisted of women only and the 70-79 years-old group which consisted of men only. Participants ranged in age from 24 to 92 years old, with a median age of 54. The distribution of participants' ages by gender is shown in Figure 1. There were 31 women and 19 men in the sample. Each age group contained both men and women except for the youngest age group (20 to 29) and oldest age group (90 to 99) which each consisted of women only and the 70 to 79 years-old group which consisted of men only. The most frequently reported travel aid was a long cane, which was used by 36 participants. Some participants reported that they use more than one kind of travel aid, choosing what they need based on the duration of the planned trip, their familiarity with the area where they will be traveling, and the anticipated lighting conditions. The use of travel aids during the study was permitted. Mobility aids such as support canes and walkers were also allowed. Eyeglasses and sunglasses were allowed, though viewing scopes such as monoculars were not allowed. Nearly all of the selected participants were legally blind as a result of limited visual acuity, limited field of vision, or a combination of the two, but all participants had some useful vision (more than light perception). None of the participants had a driver's license and all reported walking on sidewalks occasionally or frequently, either with or without travel aids. The number of participants who reported using travel aids at least occasionally is shown in Table 1. The most frequently reported travel aid was a long cane, which was used by 36 participants. Some participants reported that they use more than one kind of travel aid, choosing what they need based on the duration of the planned trip, their familiarity with the area where they will be traveling and the anticipated lighting conditions. The use of travel aids during the study was permitted. Mobility aids such as support canes and walkers were also allowed. Eyeglasses and sunglasses were allowed, though viewing scopes such as monoculars were not allowed. 8 Visual Detection of Detectable Warnings 14 Men Women 12 10 Participants 8 6 4 2 0 20 - 29 30 - 39 40 - 49 50 - 59 Age 60 - 69 70 - 79 80 - 89 90 - 99 Figure 1. Chart. Distribution of Participants' Ages by Gender 9 Visual Detection of Detectable Warnings Table 1. Self-reported Use of Travel Aids Travel Aid Long cane Dog guide Monocular/ telescope/ magnifying glasses Short cane / support cane Walker Wheel chair No travel aids used Participants Reporting Use 36 4 3 6 2 1 10 Participants' visual impairments were diverse and in several cases vision was affected by multiple medical conditions. The complete list of participants' self-reported conditions affecting their vision is given below in Table 2. The most commonly reported conditions were glaucoma, cataract, and macular degeneration. Table 2. Self-reported Medical Conditions Affecting Vision Medical Condition Glaucoma Cataract Macular degeneration / macular dystrophy Retinitis pigmentosa Optic neuritis / optic nerve atrophy Brain injury Diabetic retinopathy Retinopathy of prematurity Retinal detachment Albinism Corneal dystrophy / other corneal disease Myopic degeneration Inverse retinitis pigmentosa Uveitis Stargardt's disease Giant cell arteritis Participants Reporting Condition 13 12 10 6 6 5 5 4 3 2 2 1 1 1 1 1 1.5 Materials
Sidewalks. Four different colors of simulated sidewalk surfaces were used in this study. These included white (simulating new concrete), brown (simulating aged, dirty concrete), dark gray (simulating asphalt), and red (actual paving bricks). The four simulated sidewalk sections were constructed on low wooden platforms; each covered a 1.22 m (4 10 Visual Detection of Detectable Warnings ft) wide x 2.44 m (8 ft) long level area on the ground. The white and brown "concrete" surfaces were simulated by applying several coats of paint and sand mixture to a sheet of OSB plywood (oriented strand board). The surface texture provided by the OSB plywood and paint/sand mixture approximated the surface texture of brushed concrete. Dark gray asphalt rolled roofing material was glued on OSB plywood to simulate dark gray asphalt pavement, and red colored concrete paving bricks were laid (without mortar joints) to simulate the brick sidewalk. The surface of each simulated sidewalk section was raised approximately 76 mm (3 in.) above the ground level. Chromaticity and luminous reflectance measurements of the simulated sidewalk surfaces used in this study are given in Table 3. Detectable Warnings. Thirteen different detectable warnings were tested in this study. Ten were uniformly colored and three others had black-and-white patterns. Although two-color detectable warnings are not commonly used, we included a few high contrast patterns in this study to determine if patterns might be more effective than uniformly colored detectable warnings. Other colored patterns might have been tested but we chose to limit the number of detectable warnings used in the study to 13 so a participant could complete a full set of trials in a single two-hour session. The 10 uniformly colored detectable warnings are shown in Figure 2 with color samples. The three black-andwhite patterned detectable warnings are shown in Figure 3, photographed against the red brick sidewalk. · White · Federal Yellow · Pale Yellow · Light Gray · White Concrete · Brown Concrete · Bright Red · Orange-Red · Black · Dark Gray Figure 2. Photo. Uniformly Colored Detectable Warnings (Color Samples) 11 Visual Detection of Detectable Warnings Black with White Border (4-inch wide border) Black/White Stripes (4.5-inch wide white stripes) White with Black Border (4-inch wide border) Figure 3. Photo. Black-and-white Patterned Detectable Warnings The detectable warnings were surface-mounted composite panels provided by ADA Armor-Tile. The panels were .89 m (35 in.) x .65 m (25.5 in.) including a 13 mm (0.5 in.) smooth tapered edge on all sides. The spacing and size of the truncated domes were compliant with Federal geometric specifications (see Appendix B). The detectable warnings also had very small bumps located between and on the truncated domes to provide texture for traction. Because this study was designed to examine the relative visibility of different detectable warning colors, materials from a single manufacturer were used so that the geometric characteristics of the truncated dome pattern would be constant for all of the different colors tested. Some of the colors selected for inclusion in the study were standard colors provided by the manufacturer, and some of the colors were created by painting the detectable warning panels. The relatively thin surfacemounted detectable warnings were chosen for use in this study because they could be lifted easily by a single experimenter. However, because they were not permanently mounted according to the manufacturer's specifications, the detectable warnings had a tendency not to lie completely flat on the sidewalk. To overcome this problem, several thin metal plates were glued to the bottom of each detectable warning and magnets were embedded in the sidewalks, flush with the surface. This system served to hold the detectable warning panels flat against the sidewalk but allowed them to be quickly removed and replaced between different trials during the course of the study. When in place, the front edge of each detectable warning was positioned 1.22 m (4 ft) behind the front edge of the sidewalk and was centered horizontally on the sidewalk section. 12 Visual Detection of Detectable Warnings Blanks. Blank panels were also created for this study. Blanks were made from thin sheets of painted plastic or asphalt roofing material approximately the same size as the detectable warnings. These blanks were the same color as the sidewalks and had no truncated domes. Blanks provided very little visual contrast against the sidewalk and were included in the study to ensure that participants could not simply assume that a detectable warning was present on every trial. Like the detectable warnings, the blanks cast small shadows along their front edges which ensured that participants could not simply use the presence of a thin shadow as a cue to determine that a detectable warning was present on the sidewalk. Blank panels were used with the white, brown, and asphalt sidewalks, but not with the brick sidewalk. Chromaticity and Reflectance of Materials. Chromaticity and reflectance are physically measurable qualities that are related to the perceived color and lightness of surfaces. The chromaticity and reflectance of detectable warnings, sidewalks, and blank panel surfaces were measured in place (horizontal) at the testing site. Table 3 shows the chromaticity coordinates and reflectance factors of the materials used in this study. This set of chromaticity measurements was made between 10:00 a.m. and 11:00 a.m. under natural illumination (20% cloud cover) using a SpectraScan PR650 (PhotoResearch) spectrophotometer. The reflectance factors were measured on a different day using a Minolta CS-100 Chroma Meter. All measurements were made from the same direction that the surfaces were viewed by participants: at a downward angle of 45 degrees. Other details about the measurement procedures are given in Appendix D. Additional photometric measurements of real sidewalks at various locations in Rockville, Maryland confirmed that our simulated sidewalks had chromaticities and luminance reflectances that are plausible for actual paving materials. Chromaticity and reflectance of the actual concrete sidewalks measured varied considerably depending on th