Building More Roads
Expanding road capacity may be an important component of any longterm strategy to accommodate traffic growth in urban areas. However, there are a number of reasons why a construction-only strategy to alleviate congestion is likely not the best solution. First, increasing capacity can take years to complete and is expensive—one study found that a lane costs between $1 million and $8.5 million per mile to build. Second, new lanes are often needed in densely populated areas, but these are often also the areas where it is most difficult to find unoccupied space for expansion, making new lanes politically controversial. Third, a body of evidence suggests that the addition of a nonpriced lane to an already congested roadway may do little to alleviate congestion. This happens for two reasons: new roads generate additional traffic as drivers take trips to destinations that previously took too long to reach. And since traffic flow improves initially, drivers who were previously using alternative, often less congested routes now find the highway with the added lane more attractive. Drivers continue to redistribute themselves across the various routes until the costs of using the new route and the costs of using the existing route are about equal. At this point, no driver can be made better off by changing routes. Ultimately, the reason why building more roads is insufficient is because it does not address the underlying problem: roads are not priced and are therefore subject to overuse.