This paper describes a scalable approach to simulation of decentralized adaptive signal control
systems, motivated by our interest to provide a basis for assessing the benefit of the Surtrac
adaptive signal control system at a potential deployment site in advance of installation. The
approach centers around a simulation controller interface called VISCO, which links the VISSIM
microscopic traffic simulator to a set of externally hosted local intersection control processes.
Local control processes are free to communicate with each other and exchange control
information in the same manner that they would in a field implementation. VISCO coordinates
all interaction with the simulator process to create a distributed software-in-the-loop simulation
architecture. To illustrate and analyze the efficacy of the approach, we summarize a simulation
analysis that was conducted of the downtown triangle area of Pittsburgh PA. A 63-intersection
VISSIM model of this site is described and analyses are presented to characterize both the
efficiency of the distributed architecture and the potential utility of Surtrac adaptive control.
With respect to the former, the distributed simulation of local Surtrac control processes is found
to run in roughly 4.4 times faster than real-time, in comparison to the 14.4 times faster than real
time speed that a conventional VISSIM simulation of this model with fixed timing plans
performed. Experiments also show that the VISCO distributed architecture is effective in
significantly reducing the cost associated with VISSIM’s external COM interface. With respect
expected improvement of adaptive signal control in the downtown triangle area of Pittsburgh, the
simulation analysis shows strong benefit of Surtrac over both the existing timing plans in use in
this area and Synchro optimized plans that were generated with perfect knowledge of traffic
volumes and turning counts.