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Assignment and control in road traffic networks

Ghali, M.O. (1991). Assignment and control in road traffic networks. (Unpublished Doctoral thesis, City, University of London)


The thesis studies the traffic assignment problem in the context of:

i) deterministic queue modelling where demand and link traffic flows are time-varying, (ii) the steady-state network design problem, and (iii) signal-controlled road network.

In studying the traffic assignment problem in the context of deterministic queue modelling, a model is proposed to determine time- varying link flows in congested road networks where drivers are assumed to be cooperative in minimising total transportation costs. The model is approximate for a network of general topology where there is more than a single commodity and many bottlenecks, but optimal when there is only one active bottleneck along the routes connecting each origin-destination pair.

In regards the second context, the thesis offers a method for solving the network design problem that is similar in outer form to the method given in Marcotte (1383). The difference here is being in the way the subproblem, step 2 in Marcotte's method, is attempted. Some computational results are provided, after having implemented the method in a computer code, further, the method is compared against other familiar methods that are found in the literature.

As for studying the traffic assignment problem in the context of signal-controlled road networks, the thesis deals with time-variant and time-invariant control and traffic assignment. In both, this is done by alternating between assignment and control, so as to keep the traffic lights in tune with the link flows. Control here is expressed by means of three traffic control policies, with a view to comparing network performance under each of these policies and at different levels of congestion. The three control policies in time-invariant control and assignment are: the standard "delay minimisation" policy, as stated in Allsop (1971), the standard equisaturation method proposed by Webster (1966); and the P0 policy; introduced in Smith (1979b). The control policies in the steady state are compared within a gently rising control model that is described in this thesis to simulate the long run effect of the signal control policies on traffic redistribution. Regarding time-variant control and assignment, CONTRAM (Leonard et al (1978)) was used as an assignment program and modified to incorporate two redefined policies of the three control policies and account for vehicle occupancy.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TE Highway engineering. Roads and pavements
T Technology > TF Railroad engineering and operation
Departments: School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
School of Science & Technology > Engineering > Civil Engineering
Text - Accepted Version
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