Devices should be carefully adjusted in the field and evaluated after installation to be sure they are working properly from an engineering perspective and from the perspective of pedestrians who are visually impaired.

The sound level of the speakers must be carefully set and evaluated at the time of installation, and then checked at a time with different traffic volumes to assure that settings are correct. It is better to install APS with volumes that may be too low and adjust upwards as needed. If volumes are set too high initially, problems can arise with neighboring residents and businesses that can lead to the removal of the APS and difficulties for future installations.

Setting and evaluating sound levels

Figure 7-9. Resetting APS settings with handheld device supplied by manufacturer

Figure 7-9. Resetting APS settings with handheld device supplied by manufacturer

How to adjust APS sound levels

The controls to adjust the settings of the APS vary among the different manufacturers. The settings may be adjusted by:


Most devices require setting:

The microphone sensitivity or AGC controls how the other tones/message volumes respond to ambient noise levels. The setting must be adjusted by the installer to provide output at one of a number of ranges between the maximum and minimum. The number and width of ranges varies by manufacturer.

How loud should the sound be?

In general, installers have a tendency to set volume levels of devices too loud. Loud overhead audible signals have been problematic to neighbors of APS installations.

In addition, the loud sound of the signal may prevent pedestrians who are visually impaired from:

Installers should set volume levels according to the following guidance:

Figure 7-10. Illustration of pedestrian signals at an intersection with split phasing

Figure 7-10. Illustration of pedestrian signals at an intersection with split phasing

Figure 7-11. Channelized turn lane illustration

Figure 7-11. Channelized turn lane illustration

Volume level considerations

The correct setting will vary depending on whether there are buildings close to the APS, split phasing, or slip lanes.

Automatic volume adjustment

Pre-set automatic volume adjustment or automatic gain controls cannot assure that the volume meets the criterion for distance at which the APS should be audible. Similar automatic volume adjustment settings on APS by different manufacturers may seem to provide quite different loudness, as judged by listeners.

Measuring the sound level

Due to the short duration of pushbutton locator tone and WALK tone pulses, conventional analog or digital sound level meters are not able, in the crosswalk environment, to accurately measure the absolute sound level (dBA) of APS tones, or the sound level of APS tones relative to ambient sound.

At present, setting and evaluation of APS sound level is typically done by ear. There can be errors in making the sound too quiet or too loud. It is critical for the WALK indication to be loud enough to be audible at the crosswalk waiting location. Both the locator tone and WALK indication should be audible within 6 to 12 feet of the device, but not more than that. It has been the authors' experience that many APS installations have been set louder than was optimal either for blind pedestrians or APS neighbors.

Measuring sound where audible beaconing is needed

At crosswalks where audible beaconing is needed, sound level should be evaluated from the middle of the street, when the loud WALK indication has been called, to be sure beaconing will be provided throughout the crossing. However, current MUTCD language limits the maximum output of APS to 100 dB, and most manufacturers pre-set this maximum. Therefore, at exceptionally wide crossings, and when and where there is high ambient sound, there may be a distance in the middle of the crosswalk where the beaconing is not readily heard.

Microphone location and effect on perceived loudness

APS devices that respond to ambient sound have microphones to pick up the ambient sound.

An APS microphone should be mounted as close as possible to the position of the pedestrian who is waiting to cross the associated crosswalk, because sound pressure is halved for each doubling of the distance from the sound source in a free field.

The farther from that ideal position the microphone is for a given APS device, the greater will be the following problems.

Ideal microphone location

The best location for the microphone is as close as possible to the position of pedestrians who are waiting to cross the associated street. This results in pedestrians being clearly able to hear APS signals with no need to set the automatic volume adjustment so high that sound levels will be too high or that APS neighbors will be annoyed.

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