Design of a subnetwork controller based on MFD's and perimeter flows.:

by R. Goddijn

Institution: Delft University of Technology
Year: 2015
Keywords: MFD; subnetwork traffic control; perimeter
Record ID: 1252214
Full text PDF: http://resolver.tudelft.nl/uuid:19b53dcb-c01e-4586-8ec0-71af41e834cb


The traffic state of a road network can be described by a so called macroscopic fundamental diagram (MFD). The average production is related to the accumulation of a specific road network in this diagram. Studies have shown that the MFD could be used in an evaluation based method of a certain road network. A promising application field of the MFD is to introduce the MFD in the steering mechanism of a traffic controller. Due to increasing congestion on urban roads, extra road capacity might be needed. However, for economic reasons better usage of the current road capacity should be performed. Therewith, the intersection density in road networks has increased nowadays. One of the consequences is that the way of controlling a certain intersection influences the traffic state at another intersection. Therefore, traffic controllers should be connected when controlling traffic at individual intersections. In this thesis a subnetwork flow controller has been designed. A road network which is controlled in a hierarchical setting by a main controller can be split up in several subnetworks. By controlling the perimeter flows between the subnetworks, the traffic state of each subnetwork can be controlled. In this thesis, only traffic signals at intersections have been taken into account as the control units. The designed subnetwork flow controller had to contribute to three main objectives: 1. Maintaining a constant shaped MFD, 2. Optimizing internal flows, 3. Provide desirable perimeter flows. The subnetwork flow controller algorithm has been based upon a back pressure algorithm which belongs to the coordinated traffic responsive control strategies in existing traffic controllers. A back pressure algorithm has been chosen due to the property of balancing queues which should result in homogeneity of traffic conditions within a subnetwork. The back pressure algorithm determines pressures for every individual intersection and every traffic phase consisting of several traffic streams. For every traffic stream the downstream queue length is subtracted from the upstream queue length and multiplied with the turn ratio at which traffic can go through the intersection at that specific traffic stream. The pressure of a phase is calculated by adding up individual pressures of traffic streams which are part of that specific phase. Due to the property of balancing queues by the back pressure algorithm and the assumption that homogeneity in traffic conditions might improve internal flows, some adjustments had to be performed only in order to provide desirable perimeter flows. A maximum deviation factor has been set up which allows a certain deviation of the actual perimeter flows with respect to the desirable perimeter flows which have been set up by the main controller. When the deviation exceeds a certain value, traffic streams have to be blocked when the actual perimeter flow is too high or have to get right-of-way when the actual perimeter flow is too low. By reducing the available phases from which the subnetwork flow controller…