Abstract： We present a short geometric proof for the price of anar-
chy results that have recently been established in a series of papers on
selfish routing in multicommodity flow networks. This novel proof also
facilitates two new types of results: On the one hand, we give pseudo-
approximation results that depend on the class of allowable cost func-
tions. On the other hand, we derive improved bounds on the inefficiency
of Nash equilibria for situations in which the equilibrium travel times
are within reasonable limits of the free-flow travel times. These tighter
bounds help to explain empirical observations in vehicular traffic net-
works. Our analysis holds in the more general context of congestion
games, which provides the framework in which we describe this work.