The Valley Metro Light Rail provides service for metropolitan Phoenix, Ariz. Photo by Daniel Greene.

What Is Light Rail?

Light rail is a form of rapid transit that is an intermediate step between streetcars and heavy rail. Light rail systems are generally powered by electricity provided through overhead wires, operate on a separate right-of-way that is not grade-separated from traffic, and run one-, two- or three-car trains.

Light rail has been an integral part of mass transit systems across the world for a century, providing a great deal of diversity in light rail systems. For example, right-of-ways can be along city streets, in old railroad beds or in subway tunnels. The many examples of light rail makes it easy to identify best practices and simultaneously provides a vast array of options for best fitting light rail to a given city.

The Old and the New: Two Case Studies

The Green Line passing through Coolidge Corner. Photo by rawheadrex.

The MAX train at the Rose Quarter Transit Center. Photo by ahockley.

Perhaps the strongest argument for light rail is its remarkable resilience across time and space. Two model U.S. light rail systems—Boston’s Green Line and Portland’s MAX system—were built almost 80 years apart. Boston’s Green Line has its origins in the Tremont Street Subway, an 1897 attempt to get streetcars off downtown’s congested roads. That tunnel, the oldest subway in the Western Hemisphere, still serves as the base for America’s most used light rail system. The Green Line's daily ridership was 267,400 people in 2008. Remarkably, the routes have not been significantly changed since 1959.

The MAX system, on the other hand, only opened its first segment in 1986. Already, however, the system has 107,400 daily riders and planned expansions of the system should only increase that number.

Although there are many differences between the Green Line and the MAX system, such as different fare collection systems, different car designs, different locations for the right-of-ways and more, each is an extremely successful system integral to the health of its city.

Why Light Rail?

Light rail has distinct advantages as a transit option. While significantly cheaper than heavy rail, which can cost up to 2.5 times as much as light rail, the fixed infrastructure of light rail provides some of the same benefits. Environmentally, because light rail uses electric power, the vehicles do not directly pollute along their route. In areas with heavy local pollution, light rail can dramatically increase air quality as a result. Moreover, in areas where the electric grid draws from clean and renewable sources, using electric power is the clear green choice.

Additionally, light rail is very good at sparking development along its route. Because the trains are generally clean and quiet, and, more importantly, because the route cannot easily be changed, businesses and residents want to move near light rail. Where cities are trying to increase density and spark transit-oriented development, light rail is often a good choice.

Denser development fostered by light rail systems can also lead to even higher carbon emissions reductions because of the reduced need to travel. In other words, in denser developments, people will have more opportunities to bike, walk or take public transit, instead of riding in private cars. Better land use patterns can actually multiply the total reduction in carbon dioxide emissions by about five times. (For more details, see this study.)