We consider the problem of routing traffic to optimize the performance of a congested network. We are given a network, a rate of traffic between each pair of nodes, and a latency function for each edge specifying the time needed to traverse the edge given its congestion; the objective is to route traffic such that the sum of all travel times—the total latency—is minimized. In many settings, it may be expensive or impossible to regulate network traffic so as to implement an optimal assignment of routes. In the absence of regulation by some central authority, we assume that each network user routes its traffic on the minimum-latency path available to it, given the network congestion caused by the other users. In general such a “selfishly motivated ” assignment of traffic to paths will not minimize the total latency; hence, this lack of regulation carries the cost of decreased network performance. In this article, we quantify the degradation in network performance due to unregulated traffic. We prove that if the latency of each edge is a linear function of its congestion, then the total latency of the routes chosen by selfish network users is at most 4/3 times the minimum possible total latency (subject to the condition that all traffic must be routed). We also consider the more general setting in which edge latency functions are assumed only to be continuous and nondecreasing in the edge congestion. Here, the total

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Strange behavior may occur in networks due to the non-cooperative nature of decision making, when the latter are taken by individual agents. In particular, the well known...

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Abstract — The original Braess paradox has been predicted in a context of Wardrop equilibrium in a road traffic context where there is a continuum of (non-atomic) players. It was shown that the performance of all users at equilibrium becomes worse when adding a route. This paradox as well as various variants were also studied in the context of computer networks and telecommunications. We identify a new type of paradox occurring in wireless communications with some unusual properties with respect to previous models in which the paradox has been identified. I.

Transportation plays a vital role in the efficient movement of goods and people and forms the backbone of a countries economy. Due to the fact that the infrastructure supply cannot keep pace with increasing mobility needs and transport demand, traffic congestion has become an everyday element of life. Transportation researchers try to alleviate this problem to improve the current

Morning commuters adjust their departure times in response to day-to-day changes in congestion. Advanced Traveler Information Systems (ATIS) may enable motorists to employ fundamentally new strategies when adapting their departure times to fluctuations in congestion. At the same time, new driver strategies will likely give rise to different road network behaviors. This paper explores the mutual feedback between driver strategy and traffic system performance through a simulation model of rush hour commuting. Motorists in this model choose departure times according to three adaptive strategies. When commuters apply adaptive strategies that require ATIS in the present model, outcomes for both individual motorists and the system as a whole are by several measures worse than when drivers use a simple strategy that does not require ATIS. These results largely agree with an earlier study of a nearly identical model of rush-hour commuting. This document is available in HTML on the ...

The Braess paradox (Braess, 1968) consists of showing that, in equilibrium, adding a new link that connects two routes running between a common origin and common destination may raise the travel cost for each network user. We report the results of two experiments designed to study whether the paradox is behaviorally realized in two simulated traffic networks that differ from each other in their topology. Implementing a within-subjects design, both experiments include finite populations of paid participants in a computer-controlled setup who independently and repeatedly choose travel routes in one of two types of traffic networks, one without the added links and the other with the added links, to minimize their travel costs. Our results reject the hypothesis that the paradox is of marginal value and its force, if at all evident, diminishes with experience. Rather, they strongly support the alternative hypothesis that with experience in traversing the traffic network players converge to choosing the Pareto deficient equilibrium routes despite sustaining a sharp decline in their earnings.