Signal Phasing Considerations
Introduction
Some signalization schemes, such as exclusive pedestrian phasing and split phasing, need careful adjustment and consideration to avoid confusing pedestrians who are blind. Crossings with pedestrian signals that rest-in-WALK may need special treatment. These issues must be considered in the design phase in determining type of device and location. In addition, careful adjustment of APS volume after installation is essential.
Split phasing
Split phasing is a signal design that gives a green phase for all vehicle movements of one direction (e.g., northbound through, right, and left) followed by a phase for all movements of the opposite direction (e.g., southbound through, right, and left). At a location with split phasing, an APS that can be heard from the parallel crosswalk provides incorrect, confusing, and dangerous information. It is critical that the WALK indication be audible only from the ends of the crosswalk being signaled so pedestrians at other crosswalks do not begin to cross at a time when vehicles are turning across their path in a protected vehicular movement.
This can be accomplished by locating the APS very close to the crossing location so pedestrians can readily determine which signal applies to their crosswalk. Careful adjustment of the APS volume at all times of the day and night, as well as careful aiming of the speakers is critical. Audible beaconing may not be appropriate at locations with split phasing, due to the possibility of confusion of signals.
Possible strategies:
- An APS mounted at the pushbutton location with carefully set volume and placement to be heard only at the crossing location (see photos and further discussion in Chapter 7).
- A pushbutton that actuates the audible WALK indication only for the crosswalk that received the pedestrian call.
Actuated turn phasing
In some timing plans for actuated turn phasing, traffic in one direction may be held longer to allow the opposing traffic to complete left turning movements. In many such cases, the pedestrian phases on parallel crosswalks begin at different times. An APS that can be heard from the parallel crosswalk provides incorrect, confusing, and dangerous information and could mislead a pedestrian to cross when vehicles are turning across their path in a protected vehicular movement.
Possible Strategies:
- An APS with speakers mounted at the pushbutton with carefully set volume and very careful placement and adjustment, to be heard only at the crossing location (see photos and discussion in Chapter 7).
- A pushbutton that actuates an audible WALK indication only for the crosswalk that received the pedestrian call.
- Having the audible WALK indication sound only during that part of the WALK interval that is common to both of the parallel lanes, provided that the pedestrian clearance time remains long enough to enable pedestrians crossing with audible cues to complete their crossing before the end of the clearance interval.
Exclusive pedestrian phasing
Exclusive pedestrian phasing (also known as scramble phasing) is a signal phase when all vehicle movements are stopped and all pedestrian crosswalks are given the WALK signal. This makes it difficult for pedestrians who are blind or visually impaired to recognize the onset of the WALK interval, particularly at locations where right on red is permitted. In addition, there is no vehicle flow to aid in crossing straight to the destination corner.
In some locations, pedhead-mounted APS have been installed on all corners and two different sounds for different crossing directions have been set to sound during the WALK indication. This is not recommended, as it is confusing to all pedestrians, and the assumption of pedestrians who are blind may be that the signals are broken.
Possible Strategies:
- A pushbutton information message  was used in a pilot project in Morgantown, West Virginia, at an intersection with exclusive pedestrian phasing, in association with rapid tick walk indication . The pushbutton information message was modeled after the phase: "Wait to cross Howard at Grand. Wait for red light for all vehicles. Right turn on red permitted." During the WALK interval, all pushbutton-integrated devices at the intersection emit the same, rapidly repeating, tone. See the Morgantown case study in Chapter 9.
Rest-in-WALK
At locations where the pedestrian signal to cross the minor street rests-in-WALK, the WALK indication would sound constantly for that crossing. In many locations, that might prove to be irritating to neighbors, since the WALK would be a rapidly repeating tone, or a continuous speech message.
Possible strategy:
- Some APS manufacturers provide a limit switch that limits the length of the audible WALK indication to seven or eight seconds, but allows recall of the audible and vibrotactile indications of the WALK, if the button is pressed when there is adequate clearance time remaining. MUTCD 2009 specifically recommends limited WALK indication in Paragraph 7 of Section 4E.11. The availability of that feature should be investigated in the installation planning.
APS where pedestrian timing is pushbutton-actuated
Pushbutton-actuated pedestrian timing requires a pedestrian to locate the pushbutton and push it to request the pedestrian phase. A pedestrian who is blind needs to know a button-press is required to actuate a pedestrian timing, and needs to be able to find the pushbutton easily. The most appropriate way to convey that information is with a locator tone at the pushbutton. Pushbutton locator tones are required by the MUTCD in Paragraph 2 of Section 4E.12 which states that "An accessible pedestrian pushbutton shall incorporate a locator tone. "
Location of APS pushbuttons for actuated signals
To be useful to pedestrians who are visually impaired, pushbuttons must be installed as near to the crosswalk as possible, preferably on the sidewalk within the width of the crosswalk connection or adjacent to the crosswalk, and as close to the curb as possible.
Pedestrians who are blind must locate and push the pushbutton, and then align to cross as discussed in Chapter 2. Even with an accessible signal, a pedestrian who is blind or visually impaired may not cross on the first WALK indication, but may need to listen to traffic and the accessible signal for a cycle to confirm alignment, the signal functioning, and traffic direction before pushing the pushbutton again, realigning and crossing on the following pedestrian phase.
APS where pedestrian timing is not pushbutton-actuated
When pedestrian timing is pretimed, on recall, or called by passive pedestrian detection, pedestrians generally do not need to locate the pushbutton at the intersection. However, when installing APS, the speakers, vibrotactile WALK indication, and tactile arrow of an APS are provided at the pushbutton location. At new or reconstructed intersections, wiring and poles can be added to install the poles and APS in the recommended locations close to the crosswalk and curb ramp. Although the pushbutton may not be necessary to call the WALK indication, the other features of the APS, such as the tactile arrow, audible WALK indication, and vibrotactile WALK indication, can be beneficial to pedestrians who are blind or who have low vision.
- When an APS pushbutton with a pushbutton locator tone is installed in a location that is not close to the crosswalk, blind pedestrians may deviate from their course of travel to push the button, believing it to be necessary for the crosswalk ahead, potentially causing problems in orientation and alignment for the crossing
- Many downtown areas with wide sidewalks have pretimed pedestrian phases. Poles are rarely located in optimal locations for installation of APS with audible and vibrotactile WALK indications (see location recommendations in Figure 6-2 and 6-3)
Other option
It may be appropriate to consider other options when the addition of the APS is the only change planned at an intersection with pretimed signals. The following suggestion does not apply at new or reconstructed intersections. If a pushbutton cannot be installed in a location where the tactile arrow and vibrotactile information associated with the pushbutton is usable, it makes little sense to install an APS with those features.
Note however that an installation without the tactile arrow and vibrotactile WALK indication would not comply with the MUTCD requirements for new installations . Such an installation might be considered acceptable as a temporary measure , when existing conditions and structures prevent installation of additional poles to mount the APS beside the crosswalk.
Figure 6-4. The mast arm is used in this installation in Toronto, Canada to position pedestrian signal head and speaker closer to the crosswalk.
In that case, a pedhead-mounted APS without a pushbutton or locator tone may be appropriate. However, WALK message or tone and volume levels should be carefully determined to avoid confusion to pedestrians and to prevent disturbance to neighbors. Unless audible beaconing is determined to be necessary, the APS speaker should be oriented down toward the waiting location of the pedestrian. Use of a small mast arm to locate the APS optimally over the crosswalk location might be appropriate (Figure 6-4).
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