Issue 1: APS volume
Louder is NOT better. It is common to find APS volumes set so loud that the pushbutton locator tone and audible walk indication can be heard at midblock or across the street -- or in a quiet office or bedroom nearby. This can lead to neighborhood as well as user concerns, since excessive volume will mask other sounds that are important to pedestrians who are blind (such as the sound of traffic surges or the indication of another APS on the same corner).
An APS signal should be audible at the beginning of the crosswalk, but no more than 3.7 m (12 ft) from the pushbutton, or to the building line, whichever is closer (2003 MUTCD). Technologies that broadcast from above require higher- volume settings to be effective, and often are labeled neighborhood nuisances. Modern pushbutton-integrated devices provide the signal right where it is needed -– at the departure curb –- so it needs to provide only a 2-5 dB gain over ambient noise to signal the pedestrian interval. Click or tick tones are less apt to annoy and are more detectable in traffic noise than the older cuckoo/chirp outputs.9 They are also less likely to be confused with a bird.10 11
Remedy: When APS noise annoys, reduce the signal volume. Volume adjustments differ by manufacturer: some devices can be set through a hand-held PDA, while others require adjusting set screws on a control board mounted in the pedestrian signal head. APS volume should be set individually at every location. Note that nearby building facades or other hard surfaces that reflect the APS signal may actually cause the APS to increase in volume in reaction to its own sound, if the sound or ambient sound response is set too loud. Sound baffles may also be necessary in some locations. It’s important to adjust the APS and listen carefully. For particularly difficult situations with very near neighbors or nearby hard reflective surfaces, consider a change in sound type from a beep to a tick or click, which may be less annoying to listeners.
In most devices, the pushbutton locator tone volume and the WALK indication volume are set separately, and each has a minimum/maximum range. If there is a lot of traffic noise at some times of the day, the maximum volume of both the pushbutton locator tone and the WALK indication may need to be relatively loud, near 90 dB. However, the minimum volumes could be set in the 30 – 40 dB range to avoid annoyance at night, or when traffic volumes and ambient sound levels are low.
The response-to-ambient sound operates in conjunction with the volume settings, but is usually set separately. If the ambient sound adjustment is set to respond at 15 dB over ambient, APS are likely to be too loud when there is noise at the intersection, even if volume is appropriate for times when the intersection is quiet. The 2003 MUTCD specifies a sound volume at least 2, but no more than 5, dB over ambient.
The installer or an assistant should walk approximately 10 feet away from the device and listen to its volume during fluctuations in traffic before finalizing the volume adjustments. The installer should also listen from a distance of approximately 30 feet away. If adjusting an APS requires opening the pedestrian signal head to get to the control board to make the sound adjustments, the pedhead should be closed, and all reflective materials, such as ladders, should be moved away before this ‘final listen.’
9. Wall, R.S., D.H. Ashmead, B.L. Bentzen, & J. Barlow. Directional guidance from audible pedestrian signals for street crossing. Ergonomics. 2004. Vol. 47, (12), 1318 – 1338.
10. Carroll & Bentzen. p. 14.
11. Bentzen, Barlow & Franck, 2000, p 34.
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