Capacity Analysis for Dynamic Bottlenecks and Alternative Concepts for Coordinated Ramp Metering Operations

Project summary:

Freeway bottlenecks are, in general, caused by physical geometry changes and/or by conflicting flow patterns, such as merging or weaving flows, which reduce the maximum amount of flow that can pass a given location. While capacity of conflict-based bottlenecks is heavily dependent upon the time-variant traffic patterns within bottleneck areas, a geometry-based bottleneck, e.g., a lane-drop or a bridge with narrow shoulder, can also be wiped out by a downstream queue that grows past the bottleneck location. The capacities of both types of bottlenecks are further affected by continuously changing weather conditions. identifying active bottlenecks and estimating their time-variant capacities is of critical importance in managing congestion in freeway networks. To be sure, current Mn/DOT metering algorithm, which adopts a zone-based approach, adjusts metering rates of all the ramps in a zone such a way that the resulting flow level at downstream zone boundary, i.e., pre-defined bottleneck, can be maintained under its capacity. Therefore, the effectiveness of ramp metering control largely depends on the accuracy of bottleneck capacity values. This project addresses the above issues by developing a dynamic procedure to update capacity values for given bottlenecks. Further, as a first step to develop next generation metering algorithm incorporating ITS technologies, alternative concepts for coordinated ramp metering will be formulated in this project. The detailed algorithms that have real time operational capability will be developed in the subsequent phase.