the theory, called “induced travel,” is basically the transportation version of the law of supply and demand. Adding capacity cuts travel time, thus lowering the “price” of driving and leading to an increase in driving. In the paper, Susan Handy, a professor at UC Davis, writes that increasing a road’s capacity by 10 percent is likely to increase vehicle miles traveled by 3 percent to 6 percent in the short run and 6 percent to 10 percent in the long term. This basically offsets any gains made initially.
Handy also claims that new and widened roads don’t lead to net increases in jobs or economic activity.
So the question many are asking is does Caltrans endorse the paper? The official answer is that “solid science” shows that expanding roads does lead to more driving, so the department is fixing existing roads first and only building new roads “strategically.” Caltrans is also pushing bicycling, walking and mass transit.