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Some aspects of optimisation of traffic signal timings for time-varying demand

Han, B; (1990) Some aspects of optimisation of traffic signal timings for time-varying demand. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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The literature of applications of mathematical optimisation to the problem of setting fixed-time traffic signals at individual road junctions is reviewed. The methods developed so far have been confined largely to steady-state conditions. The research described in this thesis therefore aims to develop an optimisation technique to solve the problem of setting traffic signals for periods of time-varying demand. Previous methods of optimising traffic signal timings with respect to the total delay in the junction in a single time period are unsatisfactory especially when the junction is oversaturated. The existing program OSCADY, although it assesses performance of the junction by means of the sheared queueing formulae, optimises with respect to other criteria. Optimisation of signal timings with respect to the existing sheared delay formulae gives rise to difficulties in optimising a non-convex, non-differentiable objective function. A new sheared delay formula has been developed in order to overcome these difficulties. The properties of this formula have been investigated and optimisation of signal timings with respect to this new formula has been implemented. The results have been compared with those given by the previous method SIGSET and an approximate method that avoids the difficulties in optimisation. The comparison shows that the new formula is appropriate for use in optimising traffic signals for a single period. When traffic demands are different in successive periods, the signal settings that are optimal for each individual period, as given for example by the program OSCADY, are only local solutions to the problem. These settings may be readjusted and the changes between them shifted in time so that the overall performance for those periods taken together is improved. A sequential optimisation technique has been developed to minimise the total junction delay over the successive periods taken together by searching for the optimal signal timings and the time-shifts subject to certain queue length considerations. Some example calculations are made and the results show that such a technique can provide modest improvements in the junction control performance and give less delay than the existing methods that optimise only for individual periods. Suggestions for further research are given, together with a list of references in this field.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Some aspects of optimisation of traffic signal timings for time-varying demand
Open access status: An open access version is available from UCL Discovery
Language: English
URI: https://discovery.ucl.ac.uk/id/eprint/10123841
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