APS Prioritization Tool
As discussed previously, prioritization information is to be used in prioritizing existing intersections for retrofit with APS either in response to requests, or in updating an ADA transition plan. Prioritization schemes should place only limited emphasis on factors related to frequency or likelihood of use by blind pedestrians. The information provided by APS may be necessary at any time, along any route, to residents, occasional travelers, and visitors. Intersections having high pedestrian volumes are likely to have pedestrians whose vision is sufficiently impaired so as to have difficulty using conventional pedestrian signals.
Of greater importance in prioritizing crosswalks are factors related to determining whether sufficient acoustic information exists — at all times — to permit safe crossing at a particular intersection or crosswalk.
APS Prioritization Tool Overview
The APS Prioritization Tool was developed as part of this research (National Cooperative Highway Research Program, Project 3-62). The tool provides traffic engineers and other technical practitioners with the means to take observable characteristics of a pedestrian crosswalk and produce a rating that reflects the relative crossing difficulty for pedestrians who are blind, thus enabling prioritization of crosswalks for installation of APS. Practitioners can use this tool to determine these ratings for each crosswalk. The crosswalks with the highest ratings will have the highest priority for APS installation. While an overview of the tool and an example of use are shown in this chapter, the full instruction manual and blank Prioritization Tool forms can be found in Appendix D.
The Prioritization Tool calculates the prioritization score for a crosswalk based on characteristics of the crosswalk itself and the intersection at which it is located. Characteristics that cause a crosswalk to have a greater need for APS are assigned higher point values.
Past Rating Scales
Several rating scales have been developed in cities across the country, some of which have been utilized for over 20 years. These rating scales have been used in different ways in different cities. In some locations, they were developed as warranting schemes and APS were not installed unless the intersection met a required minimum number of points. Other cities used rating scales only to aid in prioritization.
Generally, points are assigned to specific intersection features, as well as proximity to services (such as transit, government offices, or shopping) for all pedestrians. The cities of San Diego, Los Angeles, and Portland, as well as the state of Maryland, have used point rating scales as part of their process.
The parties responsible for rating the intersections vary according to the locality. In San Diego, a traffic engineer and an O&M Specialist rate separate aspects of the intersections. In Los Angeles and Portland, the rating is conducted jointly by an O&M Specialist and a traffic engineering department staff member. In Maryland, the DOT engineer determines the rating.
Intersection Characteristics
- Number of intersection legs
- Signal design (e.g., pre-timed, actuated, etc)
- Proximity of transit facilities
- Proximity to facilities providing services for people who are blind or visually impaired
- Proximity to major pedestrian attractors (e.g., sports arena, downtown area, etc.)
Crosswalk Characteristics
- Crosswalk width
- Speed limit
- Approach and crosswalk geometrics (e.g., skewed crosswalks, large curb radii, islands or medians, etc.)
- Pedestrian signal control (e.g., pushbutton actuation required for WALK signal, leading pedestrian interval, etc)
- Vehicle signal control (e.g., right-turn-on-red, leading protected left turn phase, etc)
- Off-peak traffic presence
- Distance to alternative APS crosswalk
- Pedestrian pushbutton location
- Requests for APS
APS Prioritization Tool Validation Process
Although prior rating scales included many relevant factors, the point values assigned to these factors were not thoroughly tested in a field validation. The APS Prioritization Tool underwent validation through comparison with expert opinion from O&M Specialists and blind pedestrians. The steps in producing and validating the tool were as follows:
- The research team selected factors (e.g., crosswalk width, signal design) to include in the tool. Factors that made crossing more difficult for blind pedestrians were given higher point values. This produced the initial form of the prioritization tool.
- The team selected crosswalks in three cities (Cambridge, MA; Tucson, AZ; and Charlotte, NC). Each crosswalk was rated with the initial prioritization tool. The same crosswalks were rated by O&M specialists and blind travelers who ranked them in order of difficulty for blind pedestrians.
- The two sets of rankings were compared. The places where the prioritization tool results differed from the expert results showed where the tool's point values needed to be raised or lowered.
This process produced a tool that was validated by comparison to expert opinion in real-world situations.
Example Uses of the APS Prioritization Tool
The following example shows how the Prioritization Tool would be used to score a crosswalk that would be relatively difficult; an additional example showing a relatively easy crosswalk is included in Appendix D.
Example Crosswalk
Figure 5-1. Overhead view of Example Crosswalk (Google Earth © 2005)
Figure 5-2. Street view of Example Crosswalk
This example rates a crosswalk at a large intersection of a major arterial and a minor side street. The crosswalk of interest is on the east leg (highlighted in Figure 5-1; shown at street level in Figure 5-2).
Figure 5-3. Intersection Worksheet for Example Crosswalk
Figure 5-4. Crosswalk Worksheet for Example Crosswalk
The first worksheet deals with the intersection characteristics (Figure 5-3). Points were given for the following reasons:
- The signal is actuated but also uses split phasing, which is a higher point value than actuation, so the intersection gets the six points for split phasing. Split phasing is a less commonly used signal design, and the typically heavy turning movements make it harder to effectively use the traffic movement cue to determine signal changes. APS would provide a definitive cue to the onset of the WALK interval for pedestrians who are unable to see the pedestrian signal.
- There is a single bus route on the main street, which earns another point. The presence of public transit increases the likelihood that visually impaired pedestrians will travel at this intersection, thereby increasing the priority for APS.
There are no facilities specifically providing services for individuals who are visually impaired or major pedestrian attractors within one-half mile, so no points are given for those categories. The total intersection score is seven points.
The second worksheet deals with the crosswalk (Figure 5-4). Points were given for the following reasons:
- The crosswalk width of 110 feet and speed limit of 45 mph on the main street earn the crosswalk four and five points, respectively. Wider crosswalks and faster traffic increase the crossing difficulty and risk to visually impaired pedestrians, and APS may help expedite their crossing.
- The curb radius on one of the corners bordering the crosswalk is greater than 25 feet, so one point is given in the geometrics category. Larger curb radii create orientation problems for visually impaired pedestrians that may be decreased with the use of an APS.
- The signal requires push button actuation for the pedestrian WALK signal, so four points are given for the pedestrian signalization category. An APS locator tone would help a pedestrian who is visually impaired recognize that there is a pushbutton at that crosswalk and help in locating the pushbutton.
- Right-turn-on-red (RTOR) is permitted at the crosswalk, so two points are given in the vehicle signal control category. RTOR may produce misleading traffic cues, and an APS would provide a definitive cue of the appropriate time to cross.
- During off-peak hours, there was enough parallel traffic to provide audible cues (2 or more vehicles per cycle) about 75% of the time. This earns two points.
- There is not an alternative APS crosswalk within one-half mile, so four points are given towards the prioritization of an APS installation at this crosswalk.
- The pedestrian push button at one end of the crosswalk is located more than 10 feet from the curb, which is contrary to the recommendations in Section 4E.09 of the MUTCD. Three points are given for this drawback, since a correctly installed APS would position the push button closer to the curb which facilitates orientation alignment for blind and visually impaired pedestrians.
The crosswalk worksheet score is 25 points. When added to the intersection score of seven points, this yields a total crosswalk score of 32 points. In practice, this score of 32 points would be compared to other crosswalks under consideration for APS installations. Those crosswalks with the highest scores would have the highest priority for APS.
[ back to top ]