Crammed roadways and rush-hour traffic once were only problems in major U.S. cities such as New York and Los Angeles, but traffic snarls are becoming a growing problem for more cities. The number of metro areas where rush-hour travelers spend more than 20 hours per year stewing in traffic grew from a mere five in 1982 to 51 in 2003, according to the most recent report from the Texas Transportation Institute.

Traffic policies have long focused on road building. But some now argue that opening toll-based express lanes or instituting extra fees for rush-hour drivers -- as London did in 2003 -- may drive people toward public transportation and make commutes more efficient. Are there unintended consequences of such policies? And how big a problem is congestion if -- in the end -- commuters still are willing brave the morning rush?

The Online Journal asked economists Peter Gordon, of the University of Southern California, and Matthew Kahn, of the University of California, Los Angeles, to discuss the costs of traffic congestion, the problem it poses -- or doesn't pose -- for cities and how policy options such as London's traffic congestion charges might play on this side of the pond.