They showed that, although drivers on expanded freeways do get better gas mileage, they end up driving farther and more often, and using public transit less, with the result that air pollution and fuel consumption always show a net increase. Actually, there is no way to eliminate congestion. As long as people notice that traffic on the freeway has sped up, they will take advantage of it. As Newman and Kenworthy demonstrated, congestion is actually good, because it puts humane constraints on growth, without costing anything.
Congestion is given as a reason for widening freeways.
It is not. It is the inevitable result of excess traffic and urban sprawl. When analyzed scientifically, congestion is seen as a natural way of keeping a lid on pollution and fuel usage. In fact, congestion is one of the few tools we have for doing so. The solution is to turn to less polluting modes of transportation, as Los Angeles is finally struggling desperately to do.