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Description A very brief burst of high frequency sound, rapidly decaying to a 500 Hz WALK tone, is used by one manufacturer to alert pedestrians to the exact onset of the Walk interval. Automatic volume adjustment is also known as automatic gain control (AGC), or ambient sound adjustment. Additional information An alert tone may be particularly 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, decreasing the likelihood of conflict between pedestrians and turning vehicles. When crossings are initiated faster, pedestrians also clear the intersection faster. top 
How used An alert tone may be particularly helpful in locations with high ambient noise levels to alert pedestrians to start of a speech WALK message, or of a WALK indication that is hard to hear over traffic sound. top
References Not mentioned in Draft Public Rights-of-Way Accessibility Guidelines, MUTCD or PROWAAC. top
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