THE PREVALENCE OF BRAESS PARADOX

In a noncongested transportation network where each user chooses the quickest route, the creation of an additional route between some origin-destination pair clearly cannot result in an increase in travel time to users traveling between o-d pair. It seems reasonable to assume the same can be said of congested networks. In 1968, D. Braess presented a remarkable example demonstrating that this is not the case: a new route can increase travel time for all. The present paper gives, under reasonable assumptions, necessary and sufficient conditions for 'Braess' Paradox' to occur in a general transportation network.