CHAPTER 5

Implementation

This chapter covers two important topics to be addressed during the implementation phase of a tactile wayfinding project. First, TWSI materials need to be selected, which involves considering their durability, visual contrast, slip resistance, long-term maintenance, functionality, aesthetics, and potential contractor familiarity with the material. Second, orientation and mobility specialists need to be familiarized with the meaning of TWSIs in different contexts and then convey that information to potential users of the TWSI system. The second half of this chapter provides a quick-reference guide for orientation and mobility specialists on the basics of what TWSIs are, the terminology used to describe them, the contexts where they may be found, and the different strategies or techniques that may help travelers detect, identify, and interpret the different TWSIs and their applications.

Selecting TWSI Materials

Material Selection to Maximize Effectiveness

The research conducted during the development of this guide, along with decades of previous research, indicates that the following features of TWSI materials are key to maximizing the effectiveness of tactile wayfinding systems for pedestrians with vision disabilities:

• Visual contrast with adjacent walking surfaces: Either dark-on-light or light-on-dark. This contrast is typically provided through the TWSI itself (e.g., the tile or paver color), but some transportation agencies have also used contrasting-color borders on either side of the TWSI.
• Sufficient raised surface height for detectability: A dome or bar height of 0.2 in. (5 mm) provides good DWS and TDI detectability without creating issues for users of wheeled mobility devices. TWDs are higher, 0.75 in. (20 mm), but have more gently sloping sides. Grooved pavement, raised bars shorter than 0.16 in. (4 mm), and low-profile artistic patterns are examples of surfaces that both agency experience and research have shown are not detectable.
• Use of proven surface patterns for discriminability: The three TWSI shapes identified in this guide—dome, raised bar, and trapezoid—and pattern spacings have been shown to be discriminable from each other, which allows pedestrians with vision disabilities to understand the message being conveyed by the TWSI in a given context and react correctly. Research performed during the development of this guide showed that blank spaces work as well as raised domes to indicate choice points in a route; blank spaces are recommended to preserve the warning message conveyed by raised domes.
• Consistent use of materials for discriminability: The combination of a material’s properties, including visual contrast, dimensions, surface pattern, texture, sound, and resiliency, help users distinguish the type of TWSI being encountered and correctly interpret the message being conveyed. Using materials consistently in a TWSI system minimizes user effort needed to learn and follow TWSIs.

• Consistent use of TWSIs across agencies: It is hoped that this guide will lead to more consistent applications of TWSIs across transportation agencies, which will help pedestrians with vision disabilities more easily use TWSIs when visiting or moving to new cities.

Material Selection to Maximize Durability and Detectability

DWSs have been formally evaluated for material durability and detectability. Estakhri and Smith (2005) synthesized research and relevant information on maintaining DWSs. They list the types of materials available and examine pertinent construction, installation, maintenance, and durability topics, with snow and ice being the central maintenance considerations.

Landry et al. (2010) found that DWS detectability did not diminish when covered with a light layer of snow, but Couturier and Ratelle (2010) found that raised guide strips were difficult to follow when snow-covered and that snow does not melt any more readily on darker-colored surfaces. When frequent snow removal is required, materials such as cast iron or solid steel work better, based on field tests of different materials (Landry et al. 2010; Couturier and Ratelle 2010).

Another durability concern is the loss of visual contrast over time, including fading and reduction in color contrast (Estakhri and Smith 2005). An evaluation of certain polymeric DWS products noted the effects of sunlight on the materials, especially with regard to color fading (Na et al. 2018).

AASHTO’s National Transportation Product Evaluation Program (NTPEP) established a standard testing protocol for evaluating the long-term durability of DWS materials. Products are submitted voluntarily by manufacturers. The testing agency reports the results via the Datamine portal, and transportation agencies set local criteria for whether the products are acceptable for their specific needs (AASHTO 2019).

In general, knowledge and experience U.S. practitioners have acquired from installing and maintaining DWSs should apply to any TWSI produced with similar material and applied and maintained in similar ways (Ketola and Chia 1994; Bentzen, Barlow, and Tabor 2000). However, at the time this guide was developed, far fewer U.S. manufacturers produced standard TDI products compared to DWSs, and none produced a standard TWD product. Contractor familiarity with TDIs and TWDs relative to DWSs is expected to be similarly limited. Most of the agencies interviewed during the development of this guide had experimented with different materials, had recently installed their first tactile wayfinding system, or were in the process of developing their first system. As a result, there was little information available on the long-term durability of different materials in various settings other than for DWSs.

Material Selection to Minimize Future Maintenance

Attention to the context where TWSIs will be installed during the project’s design phase can help minimize maintenance needs after construction. Agencies interviewed provided the following insights:

• Station applications: Transit agencies tended to choose TWSI materials with consideration for their ability to withstand foot traffic and machine cleaning, along with their aesthetics. However, it is important that aesthetic considerations do not supersede functional considerations. Examples of aesthetic surfaces that eventually needed replacing include materials that did not contrast well enough with the surrounding surfaces, raised bars that were insufficiently high to be detectable, and an artistic, ropelike guidance pattern with wide diagonal bars and narrow grooves that was difficult to detect, attracted dirt, and required sandblasting to clean.
• Sidewalk applications: None of the roadway agencies interviewed had a cleaning program for their TWSIs. Instead, agencies noted a tendency for surfaces to attract dirt and lose some of

• their contrast over time, had concerns about some materials potentially being slippery when wet (e.g., early versions of cast iron strips—more recent ones are treated to be slip-resistant), or observed reduced slip resistance and material deformation over time (thermoplastic). Danish guidance (Danish Road Directorate 2013…) notes that thermoplastic TDIs wear down and lose their detectability over a period of a few years or less in busy pedestrian areas, but also notes their potential use in temporary applications in conjunction with construction projects.
• Pathway grade: Tiles and pavers may be difficult to install or keep in place where a pathway changes slope; pinning or screwing material in place may help. The Florida DOT (FDOT) requires DWSs to be pinned down due to the state’s high-water tables. FDOT’s required gap between TDI bars was developed with consideration for allowing rainwater to flow out to minimize ponding.
• Exposure to vehicle traffic: Agencies that had experimented with installing TDIs in crosswalks consistently reported that the material was quickly destroyed by vehicle traffic when installed on top of existing pavement. In a case where a metal guidance strip was installed in a sawcut in the pavement, vehicle traffic over the metal strip damaged the existing pavement to such a degree that the strip needed to be removed. TWSIs installed on curb ramps may occasionally be run over by trucks turning the corner and therefore need to be able to withstand the weight of vehicles that might occasionally run over them.
• Exposure to snowplows: NYCDOT was the only agency interviewed that had a climate with regular snowfalls. The agency has experimented with metal strips, thermoplastic, and poured-in-place concrete for various TWSI applications. Regardless of the material used, the agency reports that some TWSIs in areas used by snowplows are destroyed each time it snows.

Guidance for Orientation and Mobility Professionals

Training Potential Users

This section provides information for orientation and mobility specialists on instructing pedestrians with vision disabilities (referred to as travelers) how to use TWSIs. Different travelers may use them differently depending on the amount of residual vision they have and their travel aid (cane or guide dog). Information provided here can serve as a quick-reference foundation for orientation and mobility specialists to more simply convey to travelers the basics of what TWSIs are, terminology used to describe them, where they may be found, and different strategies or techniques that may help travelers detect, identify, and interpret the different TWSIs and their applications.

The Increasing Need for TWSIs

The built environment is becoming more complicated for pedestrians with visual disabilities to negotiate. There are more bike lanes to cross, more floating transit and bus rapid transit stops, more skewed intersections, more roundabouts, more shared streets, and more quick-build features. Many street crossings lack good tactile or auditory information for wayfinding. These changes make travel with reduced vision more confusing, more complicated, and more dangerous. TWSIs are an attempt to improve wayfinding and safety in environments where wayfinding is challenging.

The Basics

“TWSIs” is a generic term now used in the United States for walking surfaces used to aid wayfinding by pedestrians with vision disabilities. All currently used TWSIs have been demonstrated by human factors research to be readily detectable underfoot and with a long cane. TWSIs should always contrast with the surrounding surface, light-on-dark or dark-on-light.

There are three types of TWSIs: domes, raised bars, and trapezoidal. Each type calls for a different response by pedestrians with vision disabilities. Simplified, if travelers find domes, they should stop and prepare to cross a street or board a transit vehicle. If travelers find raised bars, they should either follow them to a destination or use them to align to make a crossing. If they find a trapezoid, they should not cross it; they should stay on the side closest to buildings. The other side of the trapezoid is probably for bicycles, trains, or motor vehicles.

Terminology, Descriptions, and Messages Conveyed

The technical terms for domes, raised bars, and trapezoids are detectable warning surfaces (DWSs, domes), tactile direction indicators (TDIs, raised bars), and tactile warning delineators (TWDs, trapezoidal). In the remainder of this section, the designations for the TWSIs are the short designations an orientation and mobility specialist might use with travelers of any age: domes, raised bars, and trapezoidal/trapezoids.

Domes

Domes have many names. The technical name is detectable warning surface (DWS); other common names include truncated domes and sidewalk braille. Domes have a distinctive surface pattern that has been demonstrated by human factors research to be readily detectable both underfoot and with a long cane. They are intended to let pedestrians with vision disabilities know when they are about to step into or out of a street or busy driveway, bike lane, or at-grade rail crossing; onto a median or island; or when they are at the edge of a transit platform or the edge of the boarding/alighting area for rail vehicles serving sidewalk or street-level access.

One of the most common locations for domes is near the bottoms of curb ramps. Because curb ramps are required to be within the width of crosswalks, the location of the domes on a curb ramp is a good indication that the crosswalk begins just beyond the domes. It is important to remember that although curb ramps are within the width of crosswalks, they do not always slope in the direction of travel on the crosswalk. Sometimes curb ramps slope toward the center of the intersection, so the domes should never be used to align to cross.

Domes are a minimum of 2 ft (0.6 m) deep and can be made of various materials. The domes are required to contrast visually with adjacent walking surfaces, either light-on-dark or dark-on-light. Yellow is the most common color and is required in some jurisdictions. Domes run the width of the curb ramp, not including the flares, or cover the entire area on blended transitions such as a raised pedestrian street crossing, depressed corner, or similar connections between pedestrian access routes at sidewalk level. When domes are used to indicate a crosswalk across a bike lane at sidewalk level, they will be as wide as the crosswalk.

Strips of domes are installed in pairs, one where a person goes from the pedestrian way into the vehicular way, and one where the person goes from the vehicular way back onto the pedestrian way. Domes are required on the sidewalk at each end of every crosswalk. When pedestrians with vision disabilities approach a crossing, they should stop when first encountering domes and decide whether the domes are at a crossing they want to make. The first domes encountered could be for the parallel street or a sidewalk-level bike lane. Domes encountered after a crossing is started may mean the traveler has reached the sidewalk on the other side; however, it may also mean the traveler has come to a pedestrian refuge or a median in the middle of the street, a splitter island, or a floating transit island.

Domes can also be placed all the way around corners where the curb is blended, so travelers must use other cues to be sure they are oriented to the crosswalk where they want to cross. Sometimes crosswalks are raised to sidewalk level. Where this is the case, domes should be on the sidewalk just before the crosswalk.

Domes may even be encountered before or after the street crossing if there is a sidewalk-level bike lane. Other uses are on both sides of a pedestrian refuge island that is at least 6 ft (1.8 m) wide. Large islands may have curb ramps, but smaller islands and refuges are often cut through to enable people using wheelchairs to pass through. In either case, domes are required at each side. Similar to street crossings, domes are now also required on both sides of busy driveways if the driveway approach is controlled by a traffic signal, yield sign, or stop sign.

In a single complex street crossing, for example, there may be a bike lane at sidewalk level, then a bus boarding island, then a vehicular lane or lanes, a refuge island, more vehicular lanes, then another bus boarding island, another bike lane at sidewalk level, and finally the destination corner. There are lots of places where domes are required, so context is necessary at a complex street crossing, and it is useful to remember that DWSs always come in pairs to bracket the hazardous areas. Each time domes are encountered during a complex crossing; travelers need to think about whether they are entering or leaving a vehicular way. If this aspect does not receive careful attention, users may think they have completed a crossing and are on the opposite sidewalk, but they may not have completed their intended street crossing.

Domes are also used on both sides of pedestrian at-grade rail crossings where a sidewalk or crosswalk crosses a rail line, or on transit platforms edges and the edges of sidewalk- or street-level boarding and alighting areas serving rail vehicles.

Raised Bars

The technical name for raised bars is tactile directional indicator (TDI), but they are commonly referred to as a guide strip or raised bars. Raised bars are a surface comprising parallel elongated raised flat-topped bars. Raised bars are installed in different widths and oriented differently depending on use. Raised bars should contrast visually with adjacent walking surfaces, either light-on-dark or dark-on-light. Bars are installed in four types of locations, and are used differently depending on where they are installed.

The first use is to indicate a path to follow across an open space where there are no natural guidelines. When used this way, they are in a 12-in.-wide (30.5 cm) strip with four parallel bars going in the direction of travel. Raised bars do not imply there is any danger. The bars can be crossed or followed on either side.

A second use is as a sidewalk alert when placed across a sidewalk to help locate noncorner crosswalks or bicycle-lane crosswalks. When they are used as an alert, they will be in a strip 24 in. (61.0 cm) wide. Once a traveler finds the raised bars, they can turn and follow them to the street edge or crosswalk location. In a situation where the bars are perpendicular to the direction of travel, they additionally serve as a cue for alignment.

A third use is as an alert to locate transit vehicle door opening locations. Like a sidewalk alert, they will be in a strip 24 in. (61.0 cm) wide and the bars themselves will be parallel or perpendicular to the direction of travel depending on local practices. Once a traveler finds the raised bars, they can turn and follow them to the platform edge.

A fourth use for raised bars is a physical cue for aligning to cross from corners and islands where there is insufficient or confusing information. These raised bars are not a strip but a 2 × 2 ft square of raised bars (two columns of eight bars each) placed near the edge of domes at a crossing, usually on the side farthest from the center of the intersection or on the downstream side at midblock locations, at roundabouts, and at channelized turn lane crossings. These alignment bars are perpendicular to the path of travel through the crosswalk to allow for easier alignment.

Trapezoid

The tactile warning delineator (TWD) or trapezoid is a raised linear surface that is trapezoidal in cross-section. This trapezoid is one continuous raised flat-topped surface strip wider and taller

than the bars. The top of the trapezoid is about 6 in. (15.2 cm) wide. Since it is trapezoidal, it is wider at the bottom than the top. It has very gradually sloping sides so it is not a tripping hazard despite being higher than the typical 0.2 in. (5.1 mm) allowed for the domes and bars. The trapezoid is used for delineating, for example, the boundary between a pedestrian pathway and a separated bicycle lane at sidewalk level, train tracks at sidewalk level, or between a pedestrian access route and the shared zone in a shared street. Like other TWSIs, the trapezoid should contrast visually with adjacent walking surfaces, either light-on-dark or dark-on-light.

Travelers who find a trapezoid should stay on the side closest to the building line to avoid being in the area designed for bicycles, trains, or motor vehicles.

Where Different TWSIs Might Be Found

Domes

Domes should be found at:

• Curb ramps and blended transitions at street crossings (the boundary between the pedestrian way and the street)
• Pedestrian refuge islands—cut-through pedestrian islands that are at least 6 ft (1.8 m) wide
• Pedestrian at-grade rail crossings not located in a street
• Elevated boarding platforms at transit stops where the edges are not protected by screens or guards
• Sidewalk and street-level rail boarding and alighting areas—boarding and alighting areas at sidewalk street-level rail transit stops not protected by screens or guards
• Driveways—pedestrian circulation paths at driveways controlled with yield signs, stop signs, or traffic signals

Raised Bars

Raised bars have specific indications for use: (1) guide bars are used for path delineation, (2) sidewalk alert bars are used to indicate crossing locations, (3) alignment bars are used to establish crossing alignment, and (4) transit door location bars are used to indicate where the transit door will open.

• Guide bars: A strip of raised bars 12 in. (30.5 cm) wide, oriented parallel to the path of travel, might be found:
  • – Leading to the entrance to transit stations
  • – Leading to transit station fare payment facilities
  • – Leading to fare barriers (turnstiles or gates)
  • – Across the top of bicycle ramps (raised bars parallel to the path of travel leading around the bicycle ramp to continue the path of travel on the sidewalk)

When the traveler finds the end of the strip of raised bars, they may find their destination, or they may find an empty 3 × 3 ft space used as a wayfinding junction or choice point of two guide bar paths to turn or continue following straight to their destination.

• Sidewalk alert bars: A strip of raised bars 24 in. (61.0 cm) wide oriented perpendicular to the direction of travel across an associated crosswalk or parallel to the curbline, might be used as an alert:
  • – Across a sidewalk to indicate the location of a crosswalk across a bicycle lane to a transit island
  • – Across a sidewalk to indicate the location of a noncorner crossing, such as at a roundabout, channelized turn lane, or midblock crossing (where it is also used for alignment due to lack of parallel traffic)
  • – Across a sidewalk to indicate the location of an at-grade rail crossing

• A strip of raised bars 24 in. (61.0 cm) wide oriented parallel to the direction of travel might be used as an alert:

  • – Across a transit platform for locating the vehicle door opening
  • – Across a sidewalk to indicate the location of a transit stop
• Alignment bars: A 2 × 2 ft (0.6 × 0.6 m) square of raised bars oriented perpendicular to the direction of travel on an associated crosswalk is recommended for installation adjacent to the domes on the side farthest from the center of an intersection. A 2 × 2 ft (0.6 × 0.6 m) square of raised bars oriented perpendicular to the path of travel is used to align (establish a correct heading) to cross at skewed crossings where geometric cues such as the slope of the curb ramp or acoustic cues of parallel traffic are absent, ambiguous, or misleading.
• Transit door location bars: A rectangle of TDI bars 24 × min. 36 in. (61.0 × min. 91.4 cm) with the shorter edge placed along the curbline or platform-edge DWS and the bars parallel to the curbline or platform edge, is used to indicate boarding locations.

Raised bars have sometimes been used as delineators between pedestrian zones and bicycle facilities where bike lanes are at sidewalk level. This application is discouraged because bars do not indicate any danger, and because travelers normally can cross over and walk along bars on either side without risk.

Trapezoids

Trapezoidal delineators might be found:

• Between pedestrian and bicycle facilities where bicycle lanes are at sidewalk level
• Between defined pedestrian-accessible routes and shared-use areas of shared streets
• Between defined pedestrian-accessible routes and parallel to train tracks in a sidewalk or plaza

Cane Technique for Detecting TWSIs

The constant-contact technique where the cane tip remains in contact with the ground at all times will more consistently find the domes, raised bars, and trapezoid. The two-point touch technique, only touching the walking surface at each end of the arc, is less reliable for detection. Not only does constant-contact make it easier to detect TWSIs, it will also make it easier to follow the raised bars and the trapezoid. Using the constant-contact technique is superior to any of the touch techniques, including touch-and-drag (shorelining or touch trailing), or touch-and-slide techniques.

Strategies for Using TWSIs

The following strategies assume that the domes, raised bars, and trapezoid have been installed as recommended in this guide.

Strategies for Using Domes

As the traveler approaches a street crossing, finding and using domes at corners usually entails just continuing their path of travel and the domes warn the traveler that they have reached the boundary between the pedestrian way and the vehicular way. Travelers must be aware that there are domes for both the parallel street and the perpendicular street, so they may come in contact with the domes for the parallel street before finding the domes for the street they are crossing. Domes cannot be used for alignment but will signify to the person that they are at a crosswalk.

Domes found near the corner but before the traveler arrives at the street warn of a crossing for a sidewalk-level bicycle lane. The traveler should stop and be aware that cyclists may not yield and that they may be approaching from either direction.

Domes found after leaving the corner indicate a floating transit island or a pedestrian refuge island (which may be formed as a splitter island or channelized turn-lane island). The traveler should stop and determine if another set of domes continue straight ahead, which would indicate a floating transit island or refuge island. The traveler would then continue past the second set of domes on the island and finish the crossing to the destination corner. Sometimes this crossing is completed under more than one signal phase.

When domes are found at pedestrian at-grade rail crossings, the traveler should stop and listen for approaching trains or warning bells. Trains may be traveling at a high speed, so the traveler will be safer standing back at a distance to be sure they are not in the train envelope. The traveler should listen to confirm no train is approaching from either direction before crossing.

Strategies for Using Raised Bars

The first step when a traveler finds bars is to determine or confirm how the raised bars are being used, which can be determined by situation and context (for example, is the traveler looking for a midblock crossing or the entrance to a transit station?), the width of the bars (12 or 24 in./30.5 or 61.0 cm), and the bars’ orientation.

Following Raised Guide Bars

When raised bars are determined to be 12 in. (30.5 cm), i.e., 4 parallel bars, they are intended to lead travelers across an open space and are to be followed. The guide bars do not imply any danger. The guide bars can be crossed or followed on either side. Travelers should turn so the bars are beside them on either the left or right side. Travelers can use their canes to trail the guide bars. Some travelers prefer to walk on the bars, some prefer one foot on the bars, others prefer to walk beside the bars. For instance, when locating a destination such as a transit entrance in an open area, the traveler encounters the raised guide bars, turns based on route details, and places the guide bars on either side to follow along until they reach the transit entrance.

At an intersection of guide bar paths marked by a 12-in.-wide (30.5 cm) path of parallel raised bars, a choice point (an empty 3 × 3 ft space) indicates that travelers can step into the empty space and search right, left, and ahead for the intended path of guide bars to continue following. When the bars end, the traveler determines if they are at a street crossing marked by domes, a platform edge marked by domes, or another location such as an elevator, escalator, or stairs.

Finding Crossing Locations with Sidewalk Alert Bars

The strip in this case is 24 in (61.0 cm) wide. Its length could be as short as 3 ft or as long as the sidewalk width from building to street edge. When a traveler encounters a long strip of raised bars, they would first identify the raised bars running parallel to the street or curbline. Once the traveler establishes which way to turn for the street, they can align perpendicularly underfoot and walk toward the street or curbline to locate the area for the street crossing.

Aligning with Raised Alignment Bars

When a 2 × 2 ft square of raised bars (i.e., two sets of eight bars) is encountered at a street crossing at the edge of domes farthest from the center of the intersection, travelers should use the bars to align themselves to cross. The raised bars may be detected by the traveler’s cane or underfoot. The bars will be aligned perpendicular to the direction travelers are walking, making them a physical cue for establishing a heading to cross in line with the crosswalk direction. To use the bars for alignment, travelers place both feet on the bars. Making sure the bars are perpendicular under the balls of both feet, travelers can rock forward and back and adjust until they feel aligned. Travelers may find other ways to ensure alignment.

Locating Transit Vehicle Doors

To find a boarding location along a raised platform in a station, travelers would walk parallel to the platform edge, perhaps following the DWS or a TDI guide strip, looking for a 24-in.-wide (61.0 cm) strip of raised bars across their path. The bars will be parallel to the platform edge and might extend back from the platform edge only 36 in. or they might extend farther, even all the way across the platform. Travelers would then turn and follow the bars toward the platform edge as far as desired to wait for the vehicle. The process is similar when locating an on-street bus stop, but the traveler typically would not be following DWSs or guide bars along the sidewalk. Travelers would walk close to the curbline until coming to a 24-in.-wide (61.0 cm) strip of raised bars across their path. The bars will be parallel to their path of travel along the sidewalk and might extend back from the curb only 36 in. or they might extend farther, even all the way across the sidewalk. Travelers would then turn and follow the bars (now perpendicular to their direction of travel) toward the curb as far as desired to wait for the bus.

Strategies for Using Trapezoids

When a traveler encounters a raised trapezoid, they should stop and not cross over it. The danger on the other side is an area designated for trains, vehicles, or bicycles. The traveler should stay on the side where first contact was made and turn to keep the trapezoid as a barrier to the danger area. The traveler will follow along the trapezoid until domes, raised bars, or another treatment edge is detected. When following along, the traveler should avoid sweeping the cane over to the danger side of the surface and should avoid walking on top of the trapezoid. For example, once contact with the trapezoid is made, the traveler will turn and follow to where the trapezoid ends; this point may signify the opening for a crossing location, possibly marked with raised bars and/or domes. The trapezoid may also end where another edge treatment begins, such as vegetative buffers or fencing that maintain a boundary between the pedestrian area and a vehicular area.

Using TWSIs when Traveling with a Guide Dog

There are some differences in the way guide dog users use domes, raised bars, and trapezoids. Guide dog users will only use underfoot detection. They may be going at a faster pace and have a longer stride. This means that unless they slow their pace because they know they need to find some kind of TWSI, they may step over one without detecting it. Guide dog users may orient the dog to a specific set of domes, raised bars, or a trapezoid in a route for future recognition, but travelers using guide dogs are unlikely to use raised bars for following. However, 24-in.-wide (61.0 cm) TDIs across their path of travel can alert them to the location of a noncorner crossing, transit stop, or the door opening of a transit vehicle. They can turn and walk toward the street or platform edge or follow the TDI underfoot for the short distance to the sidewalk or platform edge, where they will be in a position to cross a street or bike lane or to board a transit vehicle.

Guide dog travelers can use TDIs to align at crossings where cues provided by traffic and by the curb ramp are missing or ambiguous. Guide dogs are trained to take their handlers to the closest corner in the direction of travel when crossing streets. However, crosswalks may not end at a corner, they may be skewed, or they may not go to the closest corner. If guide dog users are at a crosswalk they know or suspect is unusual, such that their dog may not take them to the opposite end of the intended crosswalk, they should use their feet or a supplementary long cane to look for a 2 × 2 ft (0.6 × 0.6 m) square of bars close to one end of the domes. They should use this alignment square by squaring off with the bars that are perpendicular to the direction of travel across the crosswalk.

If a guide dog user encounters a trapezoidal shape underfoot, they should consider it a boundary not to be crossed and adjust their direction of travel to avoid crossing it.

Strategies for Travelers with Low Vision

TWSIs can make navigating easier for pedestrians with low vision. TWSIs should always highly contrast with the surrounding surface, dark-on-light or light-on-dark. Travelers with low vision may sometimes want to use a foot to verify the presence or direction of bars or a trapezoid.

Reasons Why TWSIs Are Sometimes Hard to Detect

Domes, bars, and trapezoids are made from an array of materials including cast iron, formed concrete, polymer composite, resilient mats, and other rigid materials that may be applied to or countersunk into the walking surface. These materials create varying sounds underfoot and with the cane. When the sound of the material being contacted by a long cane is different from the sound of the surrounding surface, detection is better. Furthermore, specific surrounding surface materials can enhance or detract from the detectability of TWSIs. For example, TWSIs in surfaces built using pavers may be more difficult to detect than those installed on smooth concrete surfaces with minimal seams, joints, or cracking. TWSIs also might be completely missed if the surrounding surface is so uneven that it is difficult to tell when a texture such as domes, raised bars, or a trapezoid are present. Slowing and really exploring with the cane and underfoot can help in this situation.

All materials wear over time, some more quickly than others, so the heights of domes, bars, and trapezoids may differ depending on how long they have been installed. Sometimes some domes or bars may be missing because they have been scraped off by snowplows or other abuse. Sometimes leaves, snow, and other debris may cover the domes or bars, making them less detectable.

Any condition that reduces tactile sensitivity may make it harder to detect changes in walking surfaces. Conditions include peripheral neuropathy in feet or hands and temporary loss of sensitivity because the feet and hands are cold, or because the shoe or boot soles are stiff or thick and resilient.

Finally, a cane user may completely miss a TWSI if they are using two-point touch with a high arc. For guide dog users and cane travelers, stepping very high can also hamper detection of TWSIs.

Disseminating TWSI Information

Orientation and mobility specialists and visually impaired travelers should advocate for installing TWSIs where there is insufficient or confusing information for nonvisual wayfinding. It is important that they be well informed about where and how TWSIs should be installed so requested installations will be accurate and consistent.

This guide can help orientation and mobility specialists, persons with vision disabilities, transportation engineers and planners, and landscape architects understand the principles of TWSIs, the specifics of which TWSI should be used for which purpose, and how a TWSI should be installed to provide the best information for users.