MUTCD Guidance MUTCD, section 4E.06, recommends: "The
installation of accessible pedestrian signals at signalized intersections
should be based on an engineering study, which should consider the following
Potential demand for accessible pedestrian signals.
A request for accessible pedestrian signals.
Traffic volumes during times when pedestrians might be present; including periods of low traffic volumes or high turn-on-red volumes.
The complexity of traffic signal phasing.
The complexity of intersection geometry."
Too little traffic is as great a problem for pedestrians who are blind as is too much traffic. In the absence of APS, blind pedestrians must be able to hear a surge of traffic parallel to their direction of travel in order to know when the walk interval begins.
Locations that may need APS include those with:
Intersections with vehicular and/or pedestrian actuation
Very wide crossings
Major streets at intersections with minor streets having very little traffic (APS may be needed for crossing the major street)
T- shaped intersections
Non-rectangular or skewed crossings
High volumes of turning vehicles
Split phase signal timing
Exclusive pedestrian phasing, especially where right-turn-on-red is permitted
A leading pedestrian interval
Where these conditions occur, it may be impossible for pedestrians who are visually impaired or blind to determine the onset of the WALK interval by listening for the onset of parallel traffic, or to obtain usable orientation and directional information about the crossing from the cues that are available.