Employment of the Traffic Management Laboratory for improving the Stratified Metering Algorithm: Phase III

Project summary:

In Phase II of this project, the evaluation results demonstrated that the stratified zone metering (SZM) strategy was generally beneficial. However, they also revealed that freeway performance was degraded by reducing the ramp delays and therefore the effectiveness of the current SZM control needed improvement. There were two objectives in this study: 1) to improve the control logic of the current SZM strategy through an estimation algorithm for the refined minimum release rate, as the simulation results indicated that the improved SZM strategy is very effective in postponing and decreasing freeway congestion while resulting in smoother freeway traffic flow compared to the SZM strategy; and 2) to improve the current queue-size estimation. Depending on the counting error of queue and passage detectors, freeway ramps are classified into three different categories, and different methods are applied respectively for improved queue-size estimation. The surveillance video data were recorded and used to verify the improvement of the proposed methods. The results indicate that the proposed methods could greatly improve the accuracy of queue-size estimation compared to the current methodology. Finally, the proposed method was evaluated by microsimulation, results of which indicated the performance of the freeway mainline was significantly improved, and that the total system performance was better than with the original SZM control.