Conventional project evaluation tends to exaggerate highway expansion economic benefits by ignoring induced travel effects (Hodge, Weisbrod and Hart 2003; Litman 2007a). Urban traffic congestion tends to maintain equilibrium; it gets bad enough to discourage further growth in peak-period vehicle trips. Expanding congested roadways tends to provide only short-term benefit because much of the additional capacity is soon filled with latent demand, peak-period vehicle trips that motorists will make if roads are uncongested but will forego (they might shift defer the trip, shift route, mode or destination) if roads are congested. .
