Reducing Real-time Crash Risk for Congested Expressway Weaving Segments Using Ramp Metering

The safety of weaving segments is a concern because of the complicated and intensive merge, diverge, and weaving maneuvers in a limited space. However, rarely did safety studies address the safety of weaving segments in simulation or apply ramp metering (RM) to improve its safety. This study first built a microsimulation VISSIM network for 16 weaving segments on an expressway to obtain the driver behavior parameters. From the traffic and safety aspects of view, the simulation network was well calibrated and validated: the simulated volume and speed were consistent with the field volume and speed, and the simulated conflicts, which were identified by the Surrogate Safety Assessment Model (SSAM), were significantly and positively related to the field crash frequency. Then, based on the validated driver behavior parameters, a microsimulation network was built for a congested weaving segment, and several RM strategies were implemented. The RM was put at the end of the on-ramp of the studied weaving segment. The RM rate was decided by a crash risk model and also by the operation condition of the mainline. The crash risk was calculated based on real-time safety analysis for weaving segments. It was found that the RM strategies could significantly reduce the conflict number and crash potential without considerable deterioration in the traffic operation of the weaving segments.