Reuters

A carefully controlled study of the Expo line shows that vehicles miles dropped 40 percent.

Los Angeles, in case you haven't heard, is doing everything in its power to shed its reputation as a car-first (or, in some minds, car-only) city. Part of that effort involves a massive expansion to the city's rail system — with six new lines slated to open between 2012 and 2020. One of these, the Expo light rail line, which runs more than 8 miles west of downtown Los Angeles toward Culver City, opened in June 2012 and is now carrying nearly 28,000 people each weekday.

The success of L.A.'s rail program will take years to determine, but an early analysis released this week suggests it's on the right track (so to speak). A research team led by Marlon Boarnet of the University of Southern California reports that the Expo Line led to significant changes in travel behavior — mostly in the desired direction. Boarnet and company found major reductions in driving and greenhouse gas emissions, as well as increases in rail ridership and physical activity.

The researchers followed about a hundred people who lived within a half mile of a new Expo Line station, and about a hundred more who lived in a comparable neighborhood nearby. In the fall of 2011, before the line began service, these test participants tracked their travel behavior for a week (logging trips, recording car odometer readings, and carrying a GPS device capable of measuring both location and physical activity). In the fall 2012, when Expo service began, the families did the same thing for another week.

The changes in driving behavior were most striking. Before Expo service began, the household travel patterns between the two types of groups looked similar. Afterward, the non-Expo group showed no statistical change in their daily vehicle-miles traveled (in fact, it increased slightly), while the Expo group reduced their daily miles driven significantly.

Overall, people near the Expo stations reduced vehicle-miles by 10 to 12 miles a day relative to those in other neighborhoods — a 40 percent drop in driving. This impact was greatest near rail stations surrounded by more bus lines and near stations on streets with fewer traffic lanes. In other words, a strong bus network and a limited road network likely enhanced transit behavior.

The researchers spotted other significant changes, too. Train trips increased among those living near the stations (as one would expect), and these households produced 30 percent fewer emissions, compared to the other households. The least active people living along the Expo line also engaged in about 8 to 10 minutes more of physical activity each day — presumably as a result of increased transit use.

What makes this study so important is its method. Most research on the impact of light rail considers broad travel patterns across wide geographical areas over many years and infers whether the rail line itself had a role in any changes. Recent work taking that approach has been mixed: there's evidence that Denver's light rail lines have made traffic better than it would have been, and little sign that light rail lines in Great Britain have produced much of a shift.

The current research on the Expo Line is, in the words of its authors, the "first-ever experimental-control group, before-after study of the impact of a major transportation investment in California" [PDF]. In simpler terms, this means the researchers tracked precise changes in actual individual travel behavior. That method gives them enough confidence to conclude that the Expo Line itself was the cause of these changes.

It's worth repeating that L.A.'s transit expansion will be assessed many ways, many times, over many years. A shift in travel behavior away from cars is only one metric (equally important is an analysis of whether the benefits were worth the massive financial investment), but it's an extremely encouraging one. Boarnet told Laura J. Nelson of the Los Angeles Times that it's still "very tough for people to wrap their minds around" the fact that the city has made a rail transit push. Findings like this make it a lot easier.

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