Lessons Learned from Existing Installations
Interfacing new APS devices with modern traffic signal control systems is not as problematic as industry initially believed. Most APS devices do not interface with traffic signal controllers at all, and those that do only provide equipment inside the cabinet. Problems experienced to date have been minor and correctable; issues presented are not dissimilar to any device associated with traffic signal systems. Many of the problems seem related to a lack of understanding by installers, who may not yet be familiar with the new types of devices, wiring, and the use of the various features. Pushbutton-integrated devices require additional wiring between the pedhead and pushbutton, more attention to pushbutton placement and alignment, and careful adjustment of sound volumes. APS devices provide a real benefit to all pedestrian movements at a signalized intersection. The information presented in this section can help those who use and/or install APS devices to avoid problems.
As with any new technology, the first installation of a new type of APS device may not always operate flawlessly. However, most are easily solvable, either by manufacturers’ adjustments to their devices or by adjustments to the installation. Key issues discussed here include:
- APS compatibility with controller MMU/Conflict Monitor;
- Wiring to pedhead and/or controller;
- Pushbutton installation;
- Signal phasing;
- Speaker positioning and volume;
- Pushbutton and pole location;
- Tactile arrow location and position;
- Use and proper wording of speech messages; and
- Braille signage and correct installation.
APS/Conflict Monitor Compatibility
APS compatibility with the MMU/conflict monitor is related to voltage issues. When unexpected voltages or voltages outside of a given range are detected, the MMU overrides the controller functions and places the signals into a flash mode until maintenance is performed. Most problems in this area have been identified by installers; manufacturers have made modifications to prevent such problems in the future.
Some of the APS devices manufactured internationally were designed with different voltage standards — voltage ranges that differ from current U.S. specifications. In reducing the voltage requirements to the pushbutton, another issue developed with one manufacturer. Some equipment was designed to send 120 VAC to the pushbutton to provide the vibrating surface during WALK, when 24 VDC or less is desired in the US. A circuit to reduce the voltage was successfully created, but the resultant circuit was external to the pedestrian wiring and therefore undetectable by the conflict monitor. In this installation, the conflict monitor would not override the conflicting pedestrian signals nor would the signals be placed into a flash mode when a pedhead malfunction occurred. The manufacturer has developed an alternative vibrating pushbutton that operates with appropriate voltage at the pushbutton and does not require an extra circuit.
Wiring Some problems have also been experienced with wiring and color code practices of devices manufactured abroad. Some device manufacturers used European or Australian wire color practices and standards. These practices are not consistent with what is commonly used in the U.S., resulting in some wiring confusion. Although NEMA and the U.S. National Electrical Code (NEC) do not specifically define system wire color codes, many locations have developed color requirements and “rules-of-thumb.” Some color codes that existed in years past have been eliminated for safety reasons assuring that technicians working with the signal wires don’t assume a wire function based on color alone. Therefore, all wires should be tested to identify its use, regardless of color. International companies have developed devices for U.S. installation but care should be taken to review the instructions and wiring of the devices to assure that devices are wired properly. Installers should not assume the function of a wire by its color.
Some of the APS devices manufactured internationally were designed with different voltage standards — voltage ranges that differ from current U.S. specifications. Particularly, foreign devices drew concern from signal technicians over the high voltage sent to the pushbutton location. Voltage to the pushbutton was originally 120 VAC, compared to 24 VDC typical in the U.S. Technicians were concerned about pedestrian safety if the push button is damaged or the push button is taken off by a passing vehicle, and a pedestrian comes in contact with the live wires or electrically charged metal pole. US models with transducers mounted in the pedestrian signal head have been developed. The problem was resolved by placing transducers in the system to reduce the voltage from the pedhead to the pushbutton location. Units with voltages common to U.S. installation are now being produced by all manufacturers listed in this report.
Some problems were initially found with the controller recognizing the pedestrian pushbutton actuation. Most pushbutton units have been found to work well with both the NEMA and 170 controllers because both (along with the conflict monitors) are sensitive to electrical deficiencies. APS devices may be more sensitive to electrical differences than a typical pushbutton. A minor electrical short, not affecting a standard pedestrian push button, prevented an APS installation from working properly. The electrical short was identified and removed using common diagnostic procedures.
Pushbuttons are often installed on the most adjacent pole to the intersection. At times, two pushbuttons with vibrotactile outputs may be installed on the same metal pole. Vibrotactile APS devices require insulation and a rubber gasket to eliminate vibrations generated from the other pushbutton. Without vibratory insulation, pedestrians may not be able to determine which device has the WALK indication since both will vibrate. Proper insulation of all pushbutton installations (or separate poles) will prevent this problem from occurring.
A potential issue with wiring of APS devices is the conflict monitor interface, making sure the device communicates with the traffic signal system. When traffic signals go into flash mode, the APS device must not remain in WALK mode. This problem can be avoided by correctly wiring the APS device into the controller/signal system so the controller logic and conflict monitor can detect and change the pedheads to the appropriate indications.
When a phase rests in WALK, either the WALK indication continues for several minutes at a time or a pushbutton is needed to start the tone, speech, and/or vibratory indications. If continuous, the WALK sound can be irritating for neighbors, even at a quiet volume, so it may be preferable to have it begin in response to actuation in residential settings. With semi-actuated phasing, a pushbutton is usually not provided when crossing alongside main street traffic since the main street approach does not have vehicular actuation. However, when the APS device is provided and the traffic signal is coordinated or on a fixed cycle, the accessible indication will not initiate until the next cycle when the pushbutton is pushed. Therefore, actuating the pushbutton will provide no information until the next signal cycle is started. Pedestrians may assume the pushbutton is not working and attempt to cross without the aid of the APS device. When the pushbutton is pushed, appropriate messaging is recommended as a speech pushbutton information message to indicate that the signal provides a walk interval on the next cycle. When this type of signal phasing is used, appropriate communication between the APS device and the signal system should be evaluated.
Another scenario caused problems with pedestrian signals that rest in WALK or DON’T WALK. A signalized intersection included a pedestrian signal to cross the side/minor street that rested in DON’T WALK unless the pedestrian pushbutton was pushed to cross that street. This signal had coordination and a fixed cycle. When the pushbutton was pushed, two results could occur: 1) if the button was pushed during the side street phase, the WALK was displayed at the start of the corresponding main street phase for a minimum time followed by the Flashing DON’T WALK and the steady DON’T WALK; 2) if the button was pushed during the corresponding main street phase, the WALK was displayed only if there was enough time for the WALK and Flashing DON’T WALK time prior to the force-off period allowed by the coordination. This installation required a time period or “window” at the beginning of the main street phase which was the only period that would allow the WALK to come up while in that phase; otherwise, the WALK would not come up until a side street phase started and terminated, i.e., the next signal cycle. Therefore, a pedestrian could activate the pushbutton and not receive a timely walk interval. Again, a pedestrian may assume that the push button is not working under this condition.
A Maryland installation experienced problems adjusting the volume of a unit that used the APS control units installed in the controller cabinet (rather than the pedestrian signal head). Because of the distance, the wiring was too small of a gauge to drive the speaker and provide a loud enough message, compounded by the pole and speaker being more than 10 feet back from the crosswalk. Manufacturer’s guidelines and specifications should be followed for proper operation. However, there were also concerns and constraints on the amount of room for new wiring in the conduit. Speakers can be provided for each control unit.
Pedhead mounted speakers in existing installations are often mounted in positions that make the messages ambiguous. The speaker should be as close as possible to the crosswalk being signaled by the speaker and speakers should be separated by 10 feet, if possible. For pushbutton integrated devices, the speaker is in the pushbutton housing. The location of the pushbutton and orientation of the speaker can be critical to hearing the WALK indication at the beginning of the crosswalk.
Although current standards call for the APS volume to be 2 to 5 dB above ambient sound and for the locator tone to be heard from 6 to 12 feet from the pushbutton, volume is often set much louder than that. Installers are used to devices using audible beaconing and think that APS are supposed to loud enough to hear across the street. While the locator tone and WALK indication volume can be measured on the street, it is difficult to get an accurate reading, because of the short duration of the tones or messages and their response to ambient noise. Installers need to understand the distance requirements for audibility of the locator tone and make adjustments to the device.
The speech messages used for the WALK indication, as well as the descriptive pushbutton message, must be understandable. Some problems have been reported. An example of this was found at an intersection where the poorly recorded WALK messages made the street names indistinguishable [“Pratt” and “Calvert”]. The recordings were made in-house and the quality of speech and accent were poor. Digital speech messages can be downloaded from an AT&T web site and use of those may be appropriate. Consistent wording and properly recorded messages are necessary for intelligibility in noisy street conditions.
Speech messages have been suggested as one method to solve problems with ambiguity when two pushbuttons were mounted on the same pole. The speech WALK message that provided the street name was supposed to clarify that the WALK message applied to the street that the pedestrian wanted to cross. However, if the speech message does not clarify which street the button applies to, the speech WALK message using the street name does not clarify which street has the WALK indication to a pedestrian who is unfamiliar with the intersection. For example, at the intersection of Harford and Taylor Streets in Baltimore, the pushbutton message just said “Harford and Taylor” (both street names) for all devices. The speech WALK messages said “Walk sign is on to cross Taylor” or “Walk sign is on to cross Harford.” This didn’t resolve the ambiguity problem for users who were unfamiliar with the intersection and not sure which street they were crossing, or who did not know which street the pushbutton applied to.
Polk County, Florida wanted to use a male voice for one crossing direction and a female voice for the other. The theory was that this difference would distinguish crossing directions and add to the safety of the crossing. Most devices provide self-recorded messages capability; however, care should be taken in recording messages, in terms of quality, and wording, and particularly ambiguity. Separate poles may be the best solution.
Other minor problems relate to the recommended messages not being used; there is no standard WALK message or standard pushbutton message. Older installations require updated messages consistent with current MUTCD standards. Recommendations for specific wording for speech messages were developed in January 2002 in a report on speech messages prepared by Accessible Design for the Blind (6). Most problems can be resolved by use of wording consistent with messages developed in that report, available online at www.accessforblind.org.
Pushbutton and Tactile Arrow Location
The blind pedestrian must push the button, then line up to cross the street. Some problems have been observed in locations of pushbuttons and poles supporting APS devices. Pushbuttons installed without locator tones may make it impossible to determine that there is a button that must be activated to call the WALK. Many problems exist with pole locations. Poles that are more than 10 feet from the curb line provide real problems activating the pushbutton and then realigning to cross the street. Pushbuttons are often placed in positions that are not reachable from the sidewalk area, are in the bushes, or behind a fence. Stub poles may be needed from some locations. Separating devices on separate poles provides greater effectiveness.
If the original installation specification was not correct, it may limit the arrow direction and location possibilities. The tactile arrow is supposed to point in the direction of travel on the crosswalk and the face of the device is supposed to be parallel to the crosswalk it controls. Some installations have the pole in a poor location, back from the street with the arrow pointing at the street and aligned with the crosswalk direction, but not within the crosswalk area. In other locations, the arrow has pointed a diagonal to the path that should be taken to cross the street. If installers do not understand the arrow’s alignment, they may install it in the wrong direction, particularly if they use the holes from the previous pushbutton.
Braille Signage Installation
Braille indications on the pedestrian signals have been found mounted backwards or with the Braille label for the wrong street. Manufacturers ship them with a label to clarify positioning; however, technicians may make adjustments to the sign and reverse or mix up the Braille plaques.