General principles in the decision:
- Provide pedestrian signal information to those who cannot see the pedestrian signal head across the street
- Provide information to pedestrians about the presence and location of pushbuttons, if pressing a button is required to actuate pedestrian timing
- Provide unambiguous information about the WALK indication and which crossing is being signaled
- Use audible beaconing only where necessary
- Put as little additional sound in the environment as possible
- Avoid disturbance of neighbors
- Allow pedestrians who are blind or visually impaired to hear the traffic sounds, as well as the APS
In many cases, a municipality or state will wish to purchase one style of APS device for all installations. However, there are engineering and design decisions in the installation of APS, as well as in the choice of equipment.
More latitude in specifications may be applied when the APS is an addition to an existing intersection. The Americans with Disabilities Act (ADA) typically requires new construction to meet ADA guidelines, while it requires additions or alterations to meet the guidelines to the maximum extent feasible. Understanding the basic considerations is necessary to designing usable installations in both new and retrofit situations.
In new construction or reconstruction, where the APS can be located consistently, it is likely possible to use standardized device features and mounting locations for all installations. When retrofitting intersections with APS, it may be necessary to use different features to provide unambiguous information at different intersections. See Chapter 4 for a listing and description of APS features.
Device location is critical to the functioning of the APS and needs to be planned. The APS may provide ambiguous information if located incorrectly, just as pedestrian or vehicular signal heads can provide ambiguous, or even dangerous, information if located incorrectly. Engineering judgment is required to determine the best way to install APS at a given intersection and crossing. Differences in curb radius, width of right-of-way, presence of a parkway (grass buffer), curb ramp design and location, and existing infrastructure on corners make each installation different.
Whenever possible, two poles should be installed for APS speakers to be located close to the pedestrian departure location and crosswalk, as described in detail below. Recommendations about location and WALK indication have been updated as a result of recent research (see Appendix C for research results).
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