The collective optimization of individual driving routes by drivers using realtime traffic maps slows everyone down. That is, everyone picking the "fastest" route on the map results in overall slowdowns. Interestingly, the solution to this problem may be to remove some roads so that drivers have fewer options for route optimization.
The authors compared the Nash equilibrium time to the socially optimal travel time, and dubbed the ratio between the two "the price of anarchy." In their study of the Boston area, which looked at travel times from Harvard Square to Boston Common, the price of anarchy at peak traffic times made for a journey that is 30 percent longer.
But the price of anarchy drops if you close a few roads, because individual drivers are less able to selfishly optimize their routes. In their analysis, the authors identified six streets in Boston and Cambridge: By closing those streets, they say, the optimal collective travel time would decrease between the two points.
(via migurski)