SUMMARY

Tactile Wayfinding in Transportation Settings for Travelers Who Are Blind or Visually Impaired

Travelers who are blind or visually impaired use a variety of cues and strategies to orient themselves in their surroundings and move through space to where they want to go. This wayfinding process can be particularly challenging in complex urban environments where some cues, such as detectable edge treatments or the sound of surging parallel traffic, may be inconsistent, confusing, misleading, or missing. Tactile walking surface indicators (TWSIs) can provide wayfinding information in such scenarios and have been used in various capacities since the 1960s. TWSIs can be any walking surface intentionally used to provide warning or guiding information through touch to people with vision disabilities. While digital wayfinding technologies have developed more recently to overcome the challenges of traveling through the built environment, not all people who are blind or visually impaired have access to or are able to use these technologies, so TWSIs are important to provide physical information.

The only standard TWSI in the United States is the detectable warning surface (DWS) of raised truncated domes. DWSs indicate the boundary between a pedestrian path of travel and a vehicular way to serve as a warning to pedestrians to check for hazards directly ahead before proceeding. They are located at the bottom of curb ramps, at blended transitions, along at-grade rail crossings, and along transit boarding platform edges and street-level rail boarding areas (Architectural and Transportation Barriers Compliance Board 2023). Research and practice internationally suggest that other TWSIs may aid in wayfinding tasks by guiding travelers along a route, marking the locations of street or rail crossings, marking where transit doors open, providing cues for establishing a heading, or delineating a boundary between a pedestrian path and a vehicular path that are at the same elevation. Two such surfaces with emerging use in the United States are the tactile direction indicator (TDI) and the trapezoidal tactile warning delineator (TWD). The TDI is a surface comprising raised parallel flat-topped elongated bars, while the TWD is one long raised element that is trapezoidal in shape when viewed in profile. There are no standards for either the TDI or the TWD in the United States, nor is there research on how different TWSIs may function effectively together as a wayfinding system.

Purpose of this Project

TWSIs must not only be detectable, but they must be identifiable and therefore discriminable from one another for the meaning of each to be successfully understood based on the context in which they are applied. Their usage within different transportation settings must also be consistently applied. This project, therefore, had three major objectives:

• Determine through empirical research the detectability, discriminability, and usability of TWSIs used together in a guidance system.

• Validate the usability of TWSIs with demonstrated detectability and discriminability under a variety of geometric and operational conditions and across a range of diverse transportation settings.
• Produce a guide that speaks to a broad audience based on those empirical results that provides consistency in design, installation, and usability of TWSIs in multimodal environments.

To begin this work, the authors prepared a research roadmap (Appendix A) that laid out what is currently known about TWSIs and what standards exists both nationally and internationally, as well as what the state of practice is for their use in the United States (Appendix B). This roadmap also identified research gaps and noted where complementary ongoing projects were helping to address them. A series of three experiments were developed to fill other gaps through this research project. Results from these experiments and this project led to conclusions that were transformed into a guidebook to aid practitioners in how to use TWSIs, issues to consider when using them, and example applications for different ways to use them.

What Is Known about TWSIs

A variety of different surface patterns have been tested to determine which are detectable by people with vision impairments. Indented or grooved patterns that have been tried in pavement surfaces are insufficient (Bentzen et al. 2000); detectability is largely influenced by the height of raised elements, the spacing between them, their dimensions, and how much pavement they cover through a pattern. Their height must be at least 0.2 in. (5 mm) to be highly detectable. This height is specified in most standards for TWSIs nationally and internationally because it is high enough for people to discern the raised elements against rough, imperfect pavements while not impeding people with mobility impairments (Bentzen et al. 1994; NITE 1998; NITE 2000; Sawai et al. 1998). To be detectable as a traveler approaches a TWSI, and to reduce the possibility of being completely stepped over in an average stride length, the TWSI needs to be 24 in. (0.6 m) deep in the direction of travel (Peck and Bentzen 1987; Mitchell 1988; Tijerina et al. 1994; Hughes 1995; O’Leary et al. 1996; Bentzen and Myers 1997; Fujinami et al. 2005). TWSIs must also have high visual contrast with surrounding surfaces (Jenness and Singer 2006; Mitani, Yoshida, et al. 2007; Mitani et al. 2009; Mitani et al. 2011).

If different TWSIs are to be used together as a wayfinding system, travelers must be able to identify which type they are encountering. The geometry of the raised elements for each TWSI pattern influences whether they can be identified underfoot or with a long cane. Japanese research in the late 1990s to early 2000s investigated a variety of combinations of different DWS and TDI geometries, resulting in some findings on a range of optimal dimensions for each surface type. The 2010 ADA Standards for Accessible Design (U.S. DOJ 2010) specifies that DWSs in the United States can have center-to-center spacing ranging from 1.6 to 2.4 in. (41 to 61 mm); however, research from Japan suggests that domes spaced 1.7 in. (43 mm) apart were not very detectable and discriminable (NITE 1998; Sawai et al. 1998; NITE 2000).

Research on TWDs mostly comes from studies done in the United Kingdom, which informed more recent research conducted in the United States that found the trapezoidal TWD (10.08-in.-wide base [256 mm], 6.33-in.-wide top [161 mm], 0.75 in. height [19 mm]) to be highly detectable, identifiable, and preferred by vision-impaired participants as the edge treatment to delineate sidewalk-level separated bike lanes from the pedestrian area (Savill et al. 1997; Childs et al. 2010; Bentzen, Scott, and Myers 2020). While the majority

of mobility-impaired participants disliked crossing the trapezoid, it was traversable due to the gradual sloping sides from base to top (Bentzen, Scott, and Myers 2020), and in practice there would be limited instances where the TWD would need to be crossed.

It is important to consider the impact TWSIs may have on people with mobility impairments, as the geometries that may make a surface more detectable and identifiable to people who are blind may be the same characteristics that cause problems for people with mobility impairments. The orientation and placement of TDIs may cause more vibration for people using wheeled mobility aids when the bars are oriented perpendicular to the direction of travel. That said, research has shown that orienting the bars this way can help pedestrians’ alignment or heading to cross at crosswalks where other cues, like the slope of the curb ramp, or traffic sounds may be missing or misleading (Takeda et al. 2006; Scott et al. 2011a; Scott et al. 2011b; Bentzen et al. 2017).

New Insights about TWSIs from This Project

Current research on the state of the practice of TWSIs in the United States does not resolve many lingering questions that became the focus of research for this project. Therefore, a series of three experiments were conducted to determine the detectability, discriminability, and usability of TWSIs used together in a guidance system in a controlled environment, and then to validate the usability of TWSIs across a range of diverse transportation settings in the field. The conduct of research for each of these experiments is laid out in depth in Chapters 4 through 6. Here, the highlights are summarized.

Given that not all geometries of DWSs currently allowed in the United States have been verified as detectable through previous research, there were concerns that the more closely spaced pattern of truncated domes may not be identifiable underfoot as domes and would therefore be difficult to discriminate from TDI bars. The first experiment sought to investigate this by testing the detection and identification of two different geometries of DWS (closely spaced vs. wider-spaced domes) and of TDI (wide, flat-topped bars vs. narrow bars with more spacing between each) in a controlled, closed-course environment. Ultimately, there was no statistically significant difference in detectability or identifiability performance between the two DWSs and two TDIs studied.

Participants detected the surfaces 95% of the time or more by cane or foot (65% by cane contact alone). With foot contact only, they correctly identified DWSs as domes and TDIs as bars on average 75% of the time. Participants generally felt that either TDI surface could be used effectively for guidance, but 20% thought the narrow bars (TDI-2) would not be as effective as the wider, flat-topped bars (TDI-1). Though Bentzen, Scott, and Myers (2020) also found no significant differences in the detectability of two TDI geometries that compared wider and narrower bars in that research, the wider bars were identified accurately at a significantly higher rate than narrower bars. Therefore, the combination of these findings with previous research resulted in selecting TDI-1, with the wider, flat-topped bars as the surface type to be used in experiments 2 and 3. Likewise, since neither DWS surface stood out as significantly better-performing, the wider dome spacing was selected to use in experiments 2 and 3 because it is the most common geometry sold in the United States.

The second experiment was designed to begin testing how DWSs and TDIs could be used together as a simple system for tasks like following paths, making turns, and finding endpoints. There were two primary objectives for experiment 2:

• Determine whether 12-in.-wide (0.3 m) TDI paths can accurately and efficiently be followed when the paths go straight or turn at 45 and 90 degrees, and that participants are able to recognize DWSs and stop when they encounter them while following a TDI path.

• Where TDI paths intersect, determine whether an indicator is needed to note the junction or choice point to improve the accuracy and efficiency of following a path that continues straight through or turns at the intersection.

Experiment 2 was also conducted in a laboratory or controlled setting where four different networks of TDI paths were arranged to test different types of path junctions (T and 4-way intersections), different choice point indicators (CPIs) to mark these junctions, and paths that went straight or turned 45 or 90 degrees. Each path ended at a DWS.

Participants were positioned on different sides of TDI paths and instructed to follow paths, turn or go straight at CPIs, and stop at DWSs. Participants could use whatever technique(s) they wished for following TDI paths, such as walking beside the bars and trailing the TDI with their cane, or walking with one or both feet on the TDI. Participants had no difficulty following straight segments of the TDI paths, but navigating path intersections proved difficult depending on the CPI present. Having no CPI (two TDI paths simply join at the intersection) performed the worst for certain scenarios, where average rates of participants successfully going in the correct direction after first reaching the intersection (e.g., turning) were as low as 50% and as high as 76% based on certain conditions. This compares to average rates of success at or above 90% when either of the other two CPIs was used. Analysis revealed that the most challenging situation occurs at T-intersections when participants traveled along the TDI path at the top of the T on the side away from the leg or stem of the T and attempted to find and turn at the path junction. They also had slightly lower success rates in navigating 45- and 90-degree turns in paths (85% and 75%, respectively) that were not at intersections. Following the TDI with regular foot contact appears to improve the participant’s likelihood of going the correct direction at a path intersection, and therefore could be a strategy to consider by certified orientation and mobility specialists (COMS) when teaching techniques to people with vision impairments on using TDI paths.

Results from experiment 2 found that some type of CPI at the junction of TDI paths is beneficial. Given there was no statistical difference in performance between a 3-ft square (0.9 × 0.9 m) CPI made of DWSs to mark an intersection of TDI paths compared to a 3 ft square of empty or blank space as the CPI, the research team proposes using the blank space. This is predicated on two lines of thought:

• DWSs are currently constrained to be used as a warning in selected locations in transportation settings where there may be hazards. Using a DWS as a CPI would broaden it to serve more generally as an attention field that could convey slightly different meanings depending on the environmental context.
• Using a blank-space CPI should be less expensive for agencies, given that there would be less TWSI material to purchase, install, and maintain.

The third experiment culminated in applying what was learned from the first two studies, combined with findings identified in the literature review, to real-world transportation settings in Charlotte, NC. This experiment sought to validate initial findings and explore how people who are blind found, identified, followed, turned at, and/or stopped and aligned in these settings using different TWSIs and other contextual and environmental cues to orient and navigate. Along with the TDI and DWS from experiment 2, a TWD was included in experiment 3. TWSIs were installed at nine different sites that represented a diversity in the types of wayfinding challenges people who are blind currently face when navigating these and similar types of settings. These nine sites and the type of TWSI treatment installed are displayed in Table 1.

Participants, who had minimal familiarization with the different types of TWSIs used and their applications, were generally able to complete the variety of tasks as instructed: following

Table 1. Experiment 3 test sites and treatments installed.

TDIs, turning as appropriate at path intersections, using TDIs to find difficult-to-locate crossing locations, and using TDIs to establish alignment headings. Where 2-ft-wide (0.6 m) TDI transit door location bars or sidewalk alert bars did not extend across the full width of a platform, walkway, or sidewalk, participants often could not find them initially (38%, 59%, or 100% successful in contacting TDI on first pass depending on the site). This suggests that where TDIs are used as alert/locator bars, with the bars perpendicular to the pedestrians’ direction of travel when boarding or crossing, they need to extend the full width of the walkway to reduce the possibility of travelers missing and walking past them on approach. Somewhat similarly, 34% of participants struggled to find and identify the square of TDI alignment bars adjacent to the DWS on the curb ramp for a skewed pedestrian street crossing, but once found, aligning to cross was good (87% established an accurate alignment when on the bars).

Once on a 12-in.-wide (0.3 m) 4-bar TDI path, participants were highly successful at following the path and navigating through choice points at path intersections with blank CPIs. However, two aspects seemed problematic for participants, possibly due to the experiment design. The first issue uncovered questions about how to “start” a TDI path: given a particular environment’s context, can better guidelines be developed for where the TDI should start, and how or what should be conveyed to people who are blind to enable them to find it? While this study sought to lay out TDI paths connecting natural access openings through a plaza to defined destinations on the other side, participants struggled to either find the start of the path or, once found, to orient in the correct heading to travel along the path in the correct direction. This may also have implications for how paths should be laid out in transit facilities and terminals to ensure people who are blind can easily find where they start/end at key features (e.g., station entrances, stairs, elevators.) The second issue is whether people with vision disabilities can successfully follow TDI paths with nonintersection turns. Based on the study design that called for participants to follow a path with an unannounced 45-degree left turn to a CPI and then turn left at the path intersection and continue to the path end, it was clear that some participants failed to turn at the CPI because they thought they had already made the left turn at the 45-degree nonintersection turn. Further research is needed to determine if certain types of turns are easier to follow (e.g., what is the maximum turning

degree for a nonintersection turn in a TDI path; are curving turns more effective than angled turns?) and to investigate how instructions for routes with turns should be relayed based on how people with vision disabilities understand turning paths.

Suggested Future Research

While some questions remain, the overall level of participant success given limited experience and training appears to validate the effectiveness of the TWSIs when employed in natural environments through experiment 3 and supports what prior research evidence has shown. Chapter 7 explores a series of research gaps to consider for future studies based on what is currently known, to continue to improve the use and applications of TWSIs and our understanding of them, including:

• How can people with vision disabilities better follow nonintersection turns?
• Are angled turns in paths easier/harder to follow than curving turns? What are the installation and maintenance considerations for each?
• Is there a maximum turning angle (e.g., range of degrees) acceptable in a TDI path before travelers cannot efficiently and successfully continue to follow the path through a turn?
• Would the use of CPIs at a nonintersection turn improve performance?
• How are turns understood by people with vision disabilities, and what messaging effectively explains the potential to encounter nonintersection turns in TDI paths through route instructions?
• As travelers become aware of and experienced in following TDI paths with turns, does that impact performance at these turns?
• How effective are TWDs in natural environmental settings as a boundary delineator to separate pedestrian travel ways from other at-grade vehicular travel ways?
• Should there be different TWSI height specifications when used indoors vs. outside?
• How should a TDI guide path begin/end?
• How long should locator TDIs (e.g., transit door location bars or sidewalk alert bars) be in relation to the walkway, sidewalk, or platform they are installed across?
• Does the use of TDI alignment squares improve through practice?
• What unique considerations may impact the performance or use of TWSIs as a system for people who use guide dogs as their travel aid?
• What is the durability of different TWSI materials (particularly for TDIs and TWDs), how should they be maintained, and what operational impacts should be considered when installed in different contexts and in different weather environments?