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Integrated traffic control at motorway bottlenecks using variable speed limits and efficient vehicles lane assignment

Skoufoulas Dimitrios-Ilias

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Summary

Motorway traffic congestion, typically initiated at bottleneck locations, is a major problem for modern societies, causing serious infrastructure degradation. According to empirical investigations, capacity flow in conventional traffic is not reached simultaneously at all lanes. Thus, traffic breakdown may occur on one lane, while capacity reserves are still available on other lanes. Naturally, once congestion appears on one lane, it spreads fast to the other lanes as well, as drivers on the affected lane attempt to escape the speed drop via lane changing. After congestion has occurred, retarded and different vehicle acceleration at the congestion head causes the so-called capacity drop phenomenon, which breeds a reduction in the mainstream flow of a motorway, while a queue is forming upstream of the bottleneck location. The most efficient way to mitigate this problem is the development and implementation of proper traffic control strategies. This thesis investigates via microscopic simulation the integrated use of two feedback control strategies utilizing Vehicle Automation and Communication Systems (VACS) in different penetration rates, aiming at maximising throughput at bottleneck locations. The first control strategy employs Mainstream Traffic Flow Control (MTFC) using appropriate Variable Speed Limits (VSL) that are communicated to all vehicles within specific controlled sections of the motorway. The second control strategy delivers appropriate lane-changing actions to selected connected vehicles, again within specific controlled sections. Simulation results demonstrated the effectiveness of the integrated use of strategies for all performance indexes considered.

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