SURTRAC: Scalable Urban Traffic Control

This paper defines and evaluates a pilot implementation of a recently developed approach to realtime, adaptive traffic signal control. The pilot system, which is called SURTRAC (Scalable Urban Traffic Control), integrates concepts from traffic control theory with recent work in the field of multi-agent planning and has several important distinguishing characteristics. First, to promote scalability and reliability, SURTRAC operates in a totally decentralized manner; each intersection independently and asynchronously allocates its green time, based on current incoming vehicle flows. Second, SURTRAC aims at managing urban (grid-like) road networks with multiple (competing) traffic flows; network-level coordination is accomplished by communicating projected outflows to downstream neighbors, which gives these intersections a more informed basis for locally balancing competing inflows while simultaneously promoting establishment of larger "green corridors". Third, SURTRAC truly operates in real-time; each intersection recomputes its allocation plan and re-communicates projected outflows as frequently as once per second in rolling horizon fashion, enabling both effective operation in tightly spaced signal networks and responsiveness to sudden changes in traffic conditions. After describing our basic approach to adaptive traffic signal control and the pilot implementation of SURTRAC, we present the results of a field test conducted on a nine-intersection road network in the East Liberty section of Pittsburgh, Pennsylvania. In this pilot test, SURTRAC is seen to achieve major reductions in travel times and vehicle emissions over pre-existing signal control.