Evaluating the Effects of Different Control Strategies on Traffic Operations at Isolated Merge Bottlenecks

The primary objective of this study was to develop variable speed limit (VSL) and ramp metering (RM) strategies that particularly focused on preventing the capacity drop and increasing the discharge flow rate at freeway merge bottlenecks, and to evaluate the effects of the proposed control strategies on traffic operations. A cell transmission model was developed to evaluate the effects of the proposed control strategies on traffic operations. The CTM was adjusted and calibrated using real- world traffic data to accurately capture the capacity drop phenomenon. With space-time diagrams and traffic characteristic diagrams, the occurrence mechanism of traffic congestion at the bottleneck under different control strategies was compared. The simulation results showed that total travel time and vehicle delay were reduced under the proposed control strategies. It was found that the VSL control and RM control were effective in improving traffic operations at freeway isolated merge bottlenecks. In addition, the RM control outperformed the VSL control in reducing traffic congestion when the on-ramp flow rate was low.