Field Evaluation of Connected Vehicle-Based Transit Signal Priority Control under Two Different Signal Plans

Abstract

In 2017, a connected vehicle (CV) corridor utilizing dedicated short-range communication (DSRC) technology was built along Redwood Road, Salt Lake City, Utah. One main goal of this CV corridor is to implement transit signal priority (TSP) when the bus is behind its published schedule by a certain threshold. With the data generated by the transit vehicles, transmitted through the DSRC system, logged by traffic signal controller, and coupled with the Utah Transit Authority (UTA) data from transit operation system, some performance data of the TSP can be analyzed including TSP requested, TSP served, bus reliability, bus travel time, and bus running time. For providing better signal coordination to buses, the signal plan for this CV corridor underwent retiming in October 2018. This research aims to compare the TSP performance before and after the signal retiming. The field data of August, September, November, and December in 2018 were selected to perform this evaluation. Results show that the TSP served rate after signal retiming is 35.29%, which is higher than that of 33.12% before signal retiming. In addition, compared with the signal plan before October, bus reliability northbound and southbound on the CV corridor was improved by 2.4% and 1.47%, respectively; bus travel time and bus running time were reduced as well.

Conditional Transit Signal Priority for Connected Transit Vehicles

“…Using the data available from this corridor, Lenard at al., found that busses equipped with CV technologies and using the TSP strategy follow their published schedule about 2%-6% more frequently than vehicles without the particular equipment (23). Another study by Wang et al also analyzed the Redwood Road corridor with an intention to evaluate CV-based TSP and changes in that evaluation after the traffic signals were recently retimed (16). In this study, conditional TSP was based on the lateness and occupancy (20% or more) of the transit vehicle.…”

“…Unconditional TSP provides priority for each transit vehicle that requests it, while conditional TSP grants priority only to transit vehicles that satisfy certain conditions, such as running behind schedule, having a certain number of passengers on board, or some another condition (15). Most big cities in the U.S. with developed transit networks, such as Seattle, Portland, Los Angeles, and Chicago, use TSP technology based on the conditional priority for vehicles behind schedule, while communication among vehicles and traffic controllers is built on infrared or loop detectors (16). TSP can be successfully applied either to isolated intersections or to coordinated corridors.…”

“…V2I communication can ensure an easy exchange of information between transit vehicles and signal controllers when a transit vehicle needs to request priority. Accurate and real-time communication is especially important if TSP depends on met conditions, such as schedule adherence, and a certain level of bus capacity utilization (16). Although CV technologies are growing in popularity, there are still a very limited number of field implementations.…”

Integrated Performance Measures for Bus Rapid Transit System and Traffic Signal Systems Using Trajectory Data

“…Additionally, various connected vehicle (CV) implementations using dedicated short range communications (DSRC) technology have been tested for enabling transit priority in the mid-2010s [28] [29]. A study in 2017 conducted by the Utah Department of Transportation found that buses equipped with CV technology improved schedule adherence by only having 35% of the TSP requests being served [30], and improved reliability by 2.65% and 1.21% after signal retiming has been performed [31].…”