Allocating Departure Time Slot to Optimize Dynamic Network Capacity

Time slot allocation is a type of traffic planning in the time-space dimensions, of which the key characteristic is that infrastructure users have to reserve a ‘slot’ on the network before departure. The mechanism of time slot allocation follows the First-In-First-Out (FIFO) principle and they are controlled by different time slot settings. Minimizing the cost of difference between cumulative desired demand and cumulative optimum demand is the main purpose for the methodology, taking capacity as a constraint. Situations with late departure only and both early and late departure with costs for non-linear programming are considered and mathematical formulations are established. The objective function, using the motorway A15 as a case study, is programmed in MATLAB and the corresponding simulations are done with Dynasmart. Several optimization algorithms were tried to see which one gives the best results. It was found that a genetic algorithm gives the best solutions, but takes the longest time to compute.

The results for the A15 motorway show that congestion has been reduced much, although there is still congestion showing up in some certain time slots. There is a 7.0% reduction in total travel time. If the values for the parameters for early and late departure are varied, it was found that the larger value of late departure is, the less congestion remains. The results demonstrate that departure time slot allocation can reduce congestion to quite some extent, migrating traffic among the time slots and highway sections.

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