October 28, 2002
COMMENTS NEEDED ON AUDIBLE TRAFFIC SIGNALS AND DETECTABLE WARNINGS
Blind people travel safely every day without adaptations to the built
environment. Moreover, suitable and sufficient alternative methods and
information are normally available to provide us full and equal access without
modification. Modifications should be considered only when sufficient nonvisual
cues are not otherwise available.
The current draft guidelines are unnecessary to make travel safe for blind
people. They would not improve access and may actually decrease safety due to
distractions created by the variety of tones added to the soundscape. For
example, adoption of the guidelines as written would result in having a locator
tone constantly beeping from each pole with a pedestrian activated push button
for the "walk/don't walk" sign. This means that mixed with all the traffic
sounds there may be as many as 8 or more separate tones all going off
simultaneously, some of which are locator tones (beeping every second when the
"don't walk" sign is on), and others which are ATS tones (beeping more rapidly
when the "walk" sign is on). This confusing array of
tones would be presented at virtually every intersection.
The draft guidelines call for detectable warnings whenever a sidewalk (including
a median or island) joins a crosswalk. However, this is not necessary to provide
accessible and safe travel for the blind. There are adequate cues available to
detect the transition from sidewalk to street. Therefore, detectable warning
should only be installed when the slope is virtually flat, referred to as 1:15
or flatter--one inch downward for every fifteen inches of sidewalk.
Audible Traffic Signals
* Most intersections do not require an ATS for the accessibility and safety of
* Only those intersections with complex geometry, complex signalization, or
varied signalization for each lane may be appropriate for an ATS.
* Vibrotactile indicators should be used in preference to audible signals in
order to minimize noise distractions and better promote safety.
* Locator tones should not be included in the final guidelines and may be
subject to further research.
* At most intersections the built environment provides ample accessible cues to
determine the difference between the sidewalk and the street.
* A slope of less than 1:15 in crossing from the sidewalk to the street
(including medians and islands) may not be detectable and should be identified
with a detectable warning.