The Fundamental Law of Road Congestion:

We investigate the effect of lane kilometers of roads on vehicle-kilometers trav-eled (VKT) for different types of roads in the United States. For interstate high-ways in metropolitan areas we find that VKT increases one for one with interstate highways, confirming the “fundamental law of highway congestion ” suggested by Anthony Downs (1962, 1992). We also uncover suggestive evidence that this law may extend beyond interstate highways to a broad class of major urban roads, a “fundamental law of road congestion. ” These results suggest that increased provi-sion of interstate highways and major urban roads is unlikely to relieve congestion of these roads. Our investigation is of interest for three reasons. First, in 2001 an average American household spent 161 person-minutes per day in a passenger vehicle. These minutes allowed 134 person-kilometer of auto travel at an average speed of 44 km/h. Multiplying by the number of households in the US and any reasonable dollar value of time, we see that the US allocated considerable resources to pas-senger vehicle travel. That Americans rank commuting among their least enjoyabl