A Statistical Analysis of the Effects of Transit Signal Priority on Bus Safety in Minneapolis, Minnesota
Transit signal priority (TSP) is a technology designed to improve the efficiency and reliability of bus service in urban areas. TSP utilizes GPS, radios, and other communication and information technology to reduce the amount of time buses have to wait at red lights. TSP systems track the location of buses and then adjust the signal timing to either extend the green or shorten the red duration at intersections, based on factors such as location, speed, and schedule status of the bus.
Although research has shown that TSP is effective at improving bus speed and reliability, researchers have not extensively studied the effects of TSP on bus safety.
To help fill this gap, the research team studied the effects of TSP on vehicle safety. First, the team gathered detailed data about a TSP deployment at 30 signalized intersections along Metro Transit bus Route 5 in Minneapolis, Minnesota. The data included stop locations, geometric features of the bus stops, bus frequency, TSP requests, and crashes. Second, the team conducted a detailed regression analysis to understand if TSP use is associated with safer driving behaviors for the bus. While crashes on Route 5 were observed to decrease in the TSP deployment period, it is important to note that due to the low number of crashes, the team used surrogate safety measures, such as the roughness of bus travel. This measure quantifies the amount of sudden braking or stopping by analyzing the trajectory of the bus as it approaches and passes through the intersection.
In the end the team found:
- TSP helps smooth bus driving behavior (e.g., less abrupt stopping and deceleration).
- TSP likely improves bus safety.
- To further enhance safety benefits from TSP, bus operational features and road geometric design factors should be considered when implementing TSP.