Travel Trends in U.S. Cities: Explaining the 2000 Census Commuting Results

As cities grow, what happens to urban form and how does that changetraffic conditions? How does growing traffic affect urban structure? Thesequestions have received considerable theoretical and empirical attention over thelast 25 years. They relate to the NIMBY debate, which associates most newdevelopment with traffic problems. Yet, until recently, substantial evidencetended to show that urban growth did not lead to "traffic doomsday". Thesefindings contradicted the standard urban model and were surprising becauseroads are mainly unpriced and perceived as a significant market failure. Manyresearchers explained the rise of suburb-to-suburb commuting (and thedispersion of employment) as a traffic "safety valve". In that case, suburbanization was more a solution than a problem. On the other hand,,recently released findings from the 2000 Census show an increase in averagecommuting times that is difficult to reconcile with the earlier findings. Whathad changed in the 1990s? This research attempts a preliminary answer to thisquestion. The key explanation may be income growth, especially in the late1990s.