1,880 research outputs found
Traffic Signal Optimization Using Cyclically Expanded Networks
Traditionally, the coordination of multiple traffic signals and the
traffic assignment problem in an urban street network are considered
as two separate optimization problems. However, it is easy to see
that the traffic assignment has an influence on the optimal signal
coordination and, vice versa, a change in the signal coordination
changes the optimal traffic assignment. In this paper we present a
cyclically time-expanded network and a corresponding mixed integer
linear programming formulation for simultaneously optimizing both
the coordination of traffic signals and the traffic assignment in an
urban street network. Although the new cyclically time-expanded
network provides a model of both traffic and signals close to
reality, it still has the advantage of a linear objective function.
Using this model we compute optimized signal coordinations and
traffic assignment on real-world street networks. To evaluate the
practical relevance of the computed solutions we conduct extensive
simulation experiments using two established traffic simulation
tools that reveal the advantages of our model
The Maximum Flow Problem for Oriented Flows
In several applications of network flows, additional constraints have to be considered. In this paper, we study flows, where the flow particles have an orientation. For example, cargo containers with doors only on one side and train coaches with 1st and 2nd class compartments have such an orientation. If the end position has a mandatory orientation, not every path from source to sink is feasible for routing or additional transposition maneuvers have to be made. As a result, a source-sink path may visit a certain vertex several times. We describe structural properties of optimal solutions, determine the computational complexity, and present an approach for approximating such flows
Routing of Electric Vehicles: Constrained Shortest Path Problems with Resource Recovering Nodes
We consider a constrained shortest path problem with the possibility to refill the resource at certain nodes. This problem is motivated by routing electric vehicles with a comparatively short cruising range due to the limited battery capacity. Thus, for longer distances the battery has to be recharged on the way. Furthermore, electric vehicles can recuperate energy during downhill drive. We extend the common constrained shortest path problem to arbitrary costs on edges and we allow regaining resources at the cost of higher travel time. We show that this yields not shortest paths but shortest walks that may contain an arbitrary number of cycles. We study the structure of optimal solutions and develop approximation algorithms for finding short walks under mild assumptions on charging functions. We also address a corresponding network flow problem that generalizes these walks
Optimizing Traffic Signal Timings for Mega Events
Most approaches for optimizing traffic signal timings deal with the daily traffic. However, there are a few occasional events like football matches or concerts of musicians that lead to exceptional traffic situations. Still, such events occur more or less regularly and place and time are known in advance. Hence, it is possible to anticipate such events with special signal timings. In this paper, we present an extension of a cyclically time-expanded network flow model and a corresponding mixed-integer linear programming formulation for simultaneously optimizing traffic signal timings and traffic assignment for such events. Besides the mathematical analysis of this approach, we demonstrate its capabilities by computing signal timings for a real world scenario
Optimizing Traffic Signal Settings for Public Transport Priority
In order to promote public transport many municipalities use traffic signal control with a priority for buses or trams. In this paper, we address the problem of finding optimal passive transit signal priority settings. Building on a cyclically time-expanded network model for the combined traffic assignment traffic signal coordination problem, we introduce a suitable queuing model and several modifications to model public transport vehicles appropriately. We evaluate the applicability of this approach by computing and analyzing optimal solutions for several instances of a real-world scenario
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