The WALK indicator should be:
High detectability essential for usability
• Large frequency component at about 880Hz
High localizability helps users:
Where the Walk interval is conveyed by tones, the tones should not be confusable with other tones in the street environment, such as vehicle backup warning beepers.
The most common tones used currently are the bird sounds like cuckoo and chirp.
Speech messages for the Walk interval must be recognizable as a WALK message and not confused with pushbutton messages or other voices at an intersection. This can partially be accomplished by use of standardized wording for speech messages. In addition, the speech message must be understandable.
It is critical that pedestrians recognize which street is being signaled and begin their crossings within the Walk interval. Unfortunately, the most common solution used in the US is ambiguous. Surveys of pedestrians who are blind and the authors' evaluation of typical overhead pedhead-mounted signals have revealed that they frequently provide ambiguous information about the crosswalk being signaled.
When the APS sound for both streets comes from the same general location, it is difficult to discriminate which street the tone or speech message applies to. The pedestrian who is blind waits to cross while standing approximately at the curb line, and may be 10 to 15 feet or more from the device speaker. The mounting of speakers does not provide clear indications of which street is being signaled, unless the speakers are mounted on two separate poles, at least 10' apart, and aligned with the crosswalk they signal.
The use of different tones for each direction requires pedestrians to know their direction of travel, and to know which tone is associated with which travel direction in a particular jurisdiction. (See discussion of Tones) While in many situations, traffic movements also help clarify the signal status, beginning to cross with the wrong signal can be a fatal mistake.
One factor that particularly affects ambiguity is location of the speakers for the WALK indication. This is discussed in the next section.
Installation as well as device selection can affect the ambiguity of the information provided by the WALK indication. Designing Installations provides more information on deciding what features would be necessary or appropriate at a particular location.
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