An alert tone is a very brief burst of high frequency sound at the beginning of the audible WALK indication, which rapidly decays to the frequency of the WALK tone. It is intended to alert pedestrians to the beginning of the WALK interval.
An alert tone may be useful if the WALK tone is not easily audible in some traffic conditions. As used in Australia, the alert tone is 14dB above the ambient sound level.
Australian engineers believe the alert tone encourages faster initiation of crossing, which decreases the likelihood of a conflict between pedestrians and turning vehicles. Also, when crossings are initiated faster, pedestrians clear the intersection faster.
When to use
An alert tone may be particularly helpful in locations with high ambient noise levels to alert pedestrians to the start of a speech WALK message, or to a tone WALK indication if it is hard to hear over traffic sound.
The 2009 MUTCD provides an option for an alert tone in Section 4E.11, P12 & P13.
How used by pedestrians who are blind or who have low vision
The alert tone gets the attention of pedestrians at the beginning of the WALK indication.
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