Introduction and Research Objectives
The Millennium Edition of the Manual on Uniform Traffic Control Devices was the first to incorporate standards for accessible pedestrian signals (APS) (1). APS is defined as a device that communicates information about pedestrian timing in a non-visual format such as audible tones, verbal messages, and/or vibrating surfaces. Chapter 4E of the MUTCD, “Pedestrian Control Features” includes criteria for the implementation of APS devices into existing traffic signal systems. Information is provided on audible tones and verbal messages, vibrotactile features, pedestrian detectors, and pushbutton locations. A task group of the Signals Technical Committee and National Committee on Uniform Traffic Control Devices (NCUTCD) led the development of the new provisions.
Several companies,located in the United States, Europe, and Australia, manufacture APS products that provide information in non-visual formats. Newer technologies provide speech, location, and mapping features at the push button; these devices have different installation requirements than the cuckoo/chirp pedhead-mounted speakers familiar to many United States traffic engineers. New APS devices are ambient sound responsive and may have tactile arrows, mapping, and speech information and location features that require different sound adjustment, wiring, and installation considerations.
APS devices that make information about the status of signal phases available to visually impaired pedestrians can provide significant benefits in usability, safety, and independence (2, 3). Nevertheless, the recent influx of new APS products has led to some confusion concerning installation criteria and compatibility with current U.S. traffic signal controller equipment. Additionally, several transportation agencies that have recently installed one or more of the APS devices have reported minor problems in their installation and operation; most have proved to be easily correctable.
Concerns with the installation of APS devices have included:
- The high voltage to the push button provided by some APS devices,
- Confusion over wiring requirements,
- Installation of two APS devices on the same pole confusing the vibrotactile information for each walk intervals,
- Controller conflicts which allow the APS to continue to provide WALK information when the traffic signal is in the flashing mode, and
- Installations that prevent the traffic conflict monitors (malfunction management units - MMU) from detecting errors in pedestrian information presentation or that send the traffic signals into flash due to voltage variations detected by the conflict monitor.
Although the APS devices in each case were installed with the best of intentions, installation deficiencies can create a real safety concern for the blind pedestrian and frustration for the traffic engineers and professionals responsible for the traffic signal system. Traffic professionals, and those who install APS devices, need to be knowledgeable on the product features and installation requirements to assure that all appropriate features are included and operate correctly.
The primary objective of this research was to provide specifiers and installers with the information needed for problem-free operation of APS devices. To fulfill this objective, detailed APS and traffic signal controller product information is provided, specifically focused on the interfacing of APS devices and traffic signal controllers. Information includes:
- Lessons learned from existing installations;
- A detailed description of available APS technologies that provide mapping, speech, and/or location features for blind pedestrians;
- Detailed information on how the APS devices interface with each traffic signal controller including:
- Wiring requirements; - Power requirements; - Interaction with conflict monitoring technology;
- A detailed description of traffic signal controllers (and manufacturers) currently used in the U.S. and those that may be available in the near future.
The following sections provide a description of each of the above items.