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Field Adjustments
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Field Adjustments

Adjustment of installations

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.
  • If the APS has been added in response to a request from a pedestrian who is blind or visually impaired, that individual should also be involved in evaluation after installation.
  • Because installers may be unfamiliar with new types of APS devices, extra supervision and attention will be required during the first few installations by any crew or contractor.
  • Even when carefully specified, installations sometimes do not match the specifications because installers do not understand that failure to exactly follow specifications may lead to an installation that cannot be accessed by pedestrians who use wheelchairs, or that could cause a pedestrian who is blind to push the wrong pushbutton, to veer into the center of the intersection, or mistake which crosswalk has the Walk interval and start crossing at an unsafe time.
  • 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.
Where should the sound be audible from?
In general, installers have a tendency to set volume levels of devices too loud.
  • The WALK indicator must be audible from the beginning of the crosswalk (MUTCD 4E.06 Standard)
  • MUTCD (4E.06 and 4E.08 Guidance) states that the locator tone and walk tone of an APS should be at the same volume (except by special actuation, providing a louder tone for a single pedestrian phase) and specifies that the locator tone should be audible 6 to 12 feet from the pushbutton, or to the building line, whichever is less.
Three settings
Most devices require setting:
  • Microphone sensitivity or automatic gain control (AGC) sensitivity,
  • Volume of the pushbutton locator tone, and
  • Volume of the WALK indication.
The microphone sensitivity or AGC controls how the other tones/message volumes respond to ambient noise levels.

Volume level considerations
The correct setting will vary depending on whether there are buildings close to the APS, and the presence of split phasing or of slip lanes.
  • When buildings are close to the APS, the sound reflected from the buildings will make the sound seem louder. The reflected sound may also influence the microphone and automatic gain control such that the APS will sound louder for the same setting than if the APS was in an open area.
  • At intersections having split phasing, APS at parallel crosswalks must not be audible across the street (at the other crosswalk), or users may begin crossing with the wrong WALK signal. Check this at times of low ambient sound as well as at times with normal sound.
  • APS at intersections having turn lanes that are channelized by a splitter island must not be audible from the corners of the intersection, before crossing the turn lane. If APS are too loud, pedestrians who are blind may believe the turn lane is signalized, or that the intersection crosswalk extends all the way to the corner. If the volume is too loud, pedestrians might assume that they have a WALK indication to begin crossing, when, in fact, they may be entering an uncontrolled, or yield or stop sign controlled, slip lane, or a separately signalized turn lane.
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