Does Light Rail Really Alleviate Highway Congestion?

Transit advocates take for granted that public rail transportation relieves congestion on the roadways, but experts consider the question far from settled. Take two influential studies published in the last few years as an example: One found the latent demand for road space so strong that even expanding public transit can't hope to diminish it, while another concluded that cities with well-established rail systems do indeed have less traffic [PDF] than those that do not. And that's just in the recent past; the debate stretches back much farther, of course.

New research by two geographers at the University of Denver nudges the literature in a hopeful direction. Focusing on light rail in Denver, Sutapa Bhattacharjee and Andrew Goetz examine the question from two angles at once: they perform a temporal analysis that compares highway traffic before and after the system opened, and a spatial analysis that measures whether or not traffic changes have taken root on highways adjacent to the rail corridor. In a paper set for publication in the Journal of Transport Geography, Bhattacharjee and Goetz believe the light rail system, if nothing else, has made the traffic situation better than it would have been: