Freeway ramp metering often exists in the vicinity of a signal-controlled diamond interchange, at which the surface street system and the freeway system intersect. Even though both systems are controlled by traffic signals, they primarily operate independently of one another. The integrated operations of a surface street system and a freeway system were studied with VISSIM, a microscopic simulation model. A traffic network consisting of a surface street and a freeway segment was constructed in VISSIM. The surface street and freeway are connected through a diamond interchange with on-ramps and off-ramps. The objective of the study was to develop an integrated control algorithm for both the diamond interchange signal and the ramp-metering signal. The proposed control algorithm, including an adaptive diamond interchange control and a traffic-responsive ramp-metering control were programmed with VISSIM's vehicle-actuated programming, which serves as an external control function for the simulation model. Preliminary tests of the proposed control algorithm indicated improved operations for both the surface street system and the freeway system. Traffic operations were significantly improved compared with nonadaptive diamond control and static ramp-metering control. Although similar performance measures were found (with the particular scenarios evaluated) with no-metering control, with the existing traffic-responsive ramp-metering control, and with the proposed traffic-responsive ramp-metering control, the proposed control algorithm has more flexibility and may be adapted over a broader range of traffic flow conditions.
Abstract