The WALK indication of many APS is provided by an audible signal such as a beep, buzz, percussive sound, or cuckoo/chirp.
Tones consisting of multiple frequencies, high and low, with a large component at 880 Hz have been found to be highly detectable and localizable in the presence of traffic sound. Frequencies above 1kHz are difficult for persons with age related upper-frequency hearing loss to detect. However for persons with normal hearing, the presence of multiple higher harmonics aids localization.
Consistency in use of a particular tone for a WALK signal is greatly to be desired, however, there is insufficient research to support technical specifications for a particular tone at this time.
Issues included in this section, that should be considered in the use of audible tones for the WALK indication are:
MUTCD 2000 (4E.06) says that WALK tones should not be confusable with other sounds in the environment, including:
MUTCD guidance in 4E.06 also recommends that care should be exercised at locations where it may be difficult to determine which APS is sounding or where an unsignalized lane may be mistaken for a signalized one due to a loud beaconing APS. Some of the issues mentioned in the MUTCD guidance regarding tones can be more successfully addressed by careful installation and volume adjustment, rather than by choosing different tones.
More discussion of this issue is in the following sections and in the section on designing installations.
Associating tones with direction of travel
Some audible pedestrian signals utilize two different tones that are associated with two different crossing directions. The most common tones used are the bird sounds like "cuckoo" and "chirp." The repeating cuckoo sound is normally used for north/south crosswalks, and the repeating chirp is normally used for east/west crosswalks. This has been the recommended signal in California and Canada.
The use of two tones for crossings in two different directions has been assumed to provide unambiguous information about which crosswalk has the WALK signal. However, research since 1988 has documented that such a system is often ambiguous.
If two tones are used, the best way to make them unambiguous is to install them so the source of each WALK tone is localized in the area of the pedestrian waiting to cross the associated crosswalk, and speakers on a corner are separated by a minimum of 10 feet (MUTCD 4E.08).
Use of additional tones
Some APS products have the capability of producing more than two different tones to accommodate intersections having more than two intersecting streets. But note that
In Europe and Australia, tones are used successfully to indicate the Walk interval from pushbutton integrated APS. There is some variability in the tones used. Typically, the tone for WALK is the same tone as the locator tone, repeated at a faster repetition rate, usually 5 to 10 times faster. The same tone is used for all crossing directions.
The standardized location of the pushbutton in relation to the crosswalk makes it obvious to users which crosswalk has the Walk interval. In all locations, pedestrians are beside the appropriate APS when they are waiting to cross, normally within arm's reach of the APS, and at some distance from the APS for another crosswalk.
Other issues besides specific tone may increase the value for directional alignment and beaconing more than the tone, per se. For example, the presence of a quiet locator tone on the opposite curb during the clearance interval may make more difference in the ability of users to home in on the destination corner, than the choice of a particular WALK tone that normally ceases to sound when the pedestrian is only part way across the crosswalk.
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