It can if it's built right, as in Portland or San Diego, and new research explains why.
We often think of light rail as a single component of a larger transit system, but if it's done right it can just as soon serve as the foundation. Since 1981 a dozen American cities have built light rail lines atop bus-only systems. In five of them — Dallas, Portland, Sacramento, Salt Lake City, and San Diego — light rail now accounts for at least 30 percent of all transit ridership in the metropolitan area, even as it covers less than that much service space in the region.
Transit researchers Gregory Thompson and Jeffrey Brown of Florida State, known for their espousal of multi-destination transit systems, recently took a closer look at these light rail systems to determine what characteristics define the best of the best. In a recent issue [PDF] of the Journal of Public Transportation, Thompson and Brown identify two of these "backbone" systems in particular — Portland and San Diego — as far more efficient than the others.
Thompson and Brown settled on three key factors in the success of these systems. First, a great light rail system anchors a transit network that's dispersed throughout a metro area. Second, it acts as an express regional alternative to the local bus network. And third, it promotes transfers between the bus and rail systems. The researchers believe these traits can serve as guides for future light rail planners "by setting forth attributes that these services need to possess in order to attract substantial ridership."
In good Olympic spirit, the researchers then judged all five of the above "backbone" systems and gave them scores of up to five points on each success marker, for a possible total of 15 points. Here's how the light rail systems placed, from highest- to lowest-scoring. (Caveat: the data were collected circa 2007, which made the evaluations especially unfavorable to Salt Lake City's popular TRAX system, so we've omitted that here.)
Score: 12 out of 15
Thompson and Brown gave Portland's MAX (Metropolitan Area Express) light rail system 4 out of 5 points on each of their three criteria. MAX accounts for 39 percent of metro area transit ridership despite covering just 19 percent of the entire service area. The dispersed nature of the city's transit network is clear from the fact that its most heavily patronized bus routes don't serve the CBD. MAX operates at roughly twice the speed of the local bus lines and serves major employment centers both east and west of downtown Portland. Last, as you would expect from a well-integrated system, the MAX stations with the highest boarding figures are transfer centers, even outside the CBD.
Score: 12 out of 15
The San Diego Trolley earned the same score as Portland with the same breakdown. (The city, whose transit plans were evaluated here, now has a light rail system called the SPRINTER as well.) The Trolley serves more than 208 million passenger miles a year—44 percent of the metro area's entire ridership, on just 22 percent of its total service area. San Diego's transit network is even more decentralized than Portland's, write Thompson and Brown, with many bus routes terminating at light rail stations rather than continuing into the CBD as they once did. The system covers major job centers outside the downtown area, particularly the edge area of Mission Valley. It operates with greater frequency than the region's commuter rail, and both greater frequency and speed than express buses. Most of the transfer stations experienced an increase in patronage in recent years, with the exception of those in the CBD.
Score: 7 out of 15
The DART light rail system in Dallas carries 30 percent of metro area riders on just 13 percent of service area in the region. Still Thompson and Brown awarded it just 2 out of 5 points on being part of a dispersed network, with the middle third of the Dallas-Fort Worth metro area unserved by transit. The researchers gave it 3 out of 5 as an overlay of the bus system, saying its frequency is too low to function as the high-speed backbone of a regional network. On transfers DART received another score of 2 out of 5, primarily because the Dallas and Fort Worth regions aren't well integrated. Generally the researchers felt the system performs well in Dallas, but not in the metro area as a whole.
Score: 7 out of 15
Sacramento's RT light rail system earned the same scores as the DART system across the board. RT accounts for a full half of the metro area's transit ridership — roughly 78 million passenger miles a year — on a little over a quarter of the region's total service area. Thompson and Brown argue that the city's transit coverage became less efficient after light rail extensions, built in 2000, that didn't work together with the bus system. The RT extension to Folsom, for instance, runs near areas of high employment but fails to connect with them. These two shortcomings limit the effectiveness of transfers on the light rail system.