Anticipate and address challenges to consistently operating a transit signal priority (TSP) system.
Experience from a cooperative project between Sacramento County and the Sacramento Regional Transit District in deploying a transit signal priority system.
- Allocate sufficient time to calibrate TSP emitters. The Sacramento County manually determined the distance at which the TSP signal controller becomes aware of the presence of an emitter-equipped bus. This trial-and-error process required multiple test runs at each TSP equipped intersection in order to account for the various factors that affect signal strength and detection distance. For example, the horizontal alignment of the roadway leading up to the intersection as well as the distance between a bus stop and an intersection affect the calibration of the TSP emitters. While the process is time intensive, it is a critical factor in the successful operation of a TSP system.
- Install TSP emitters that require minimal input from the vehicle operator. While most TSP emitters operate automatically when the bus door is in the closed position, the TSP units deployed in the Watt Avenue project required the vehicle operator to manually activate the system via an operator switch. Although bus operators received initial training on how to operate the TSP system, misconceptions about how to operate the system resulted in numerous instances were TSP equipped buses were operating without the TSP emitter systems being activated. In order to eliminate operator interface, as additional TSP units were purchased, activation of the systems were hardwired to the door mechanism.
- Establish "test signals" to verify proper functioning of the TSP emitters. In order to quickly identify faulty emitters it is recommended that a "test signal" be placed at the exit door of the bus depot. The "test signal" would display a green light to drivers upon exit only when their emitters were properly functioning. Such a system would allow operators to immediately recognize and address any functionality problems with the TSP emitters.
- Anticipate and plan for challenges in consistently assigning emitter-equipped buses to the TSP routes. The RT found it difficult to ensure that emitter-equipped buses were consistently assigned to the Watt Avenue route. The primary reason is that vehicle route assignments are made by maintenance staff; while schedulers can request that only emitter-equipped buses be assigned to a particular route, the request may not be met depending upon the number of buses that are out of service that day.
The results of the transit mobility and performance analysis for the Watt Avenue TSP project found that the average travel time for TSP equipped buses was between 14 and 71 seconds less than for non-TSP buses traveling over the same segments, amounting to a 4 percent decrease in bus travel time. However, TSP buses did not experience a statistically significant increase in travel time reliability. As these lessons demonstrate, there are a number of challenges to consistently and adequately operating the transit signal priority system. Without consistent use of equipped buses and functioning signals, benefits beyond sporadic time savings, such as overall schedule adherence and improved customer satisfaction, are difficult to achieve.
Author: Jennifer Rephlo and R. Hass, Science Applications International Corporation (SAIC)
Published By: Prepared by SAIC for the USDOT FHWA
Source Date: 4/14/2006
EDL Number: 14299URL: http://ntl.bts.gov/lib//jpodocs/repts_te//14299.htm
Science Applications International Corporation
Sacramento Regional Transit District
Volpe National Transportation Systems Center
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bus priority, traffic signals, TSP