Cap’n Transit described diesel multiple units (DMU) as “light rail” in a post about the Federal Railroad Administration’s relaxing of safety rules that mostly prevented DMUs from operating on freight lines. A DMU is a passenger rail car with a built-in diesel engine, so it doesn’t need to be pulled by a dedicated locomotive. Similarly, an electric multiple unit, or EMU is a passenger car with a built in electric motor; all Link cars are EMUs. The Cap’n Transit post struck me as odd: I had never heard of DMUs describe das “light rail” before. It got me thinking: what exactly does “light rail” mean?
Generally, “light rail” is used to describe systems that are somewhere in the middle of the passenger train spectrum in terms of passenger capacity and speed. On the low end of that spectrum are streetcars and trams, and on the high end are large-capacity rail systems like the New York City subway or the DC Metro. The distinction isn’t always very useful, some “light rail” systems have capacities that are similar to larger “heavy rail” metros and some so-called “heavy-rail” systems have speeds that compare to that of streetcars. Still, any local or regional system that has a significant number of at-grade crossings is typically described as light rail.
The surprise I had with the description of DMUs as light rail is that I have mostly seen DMUs used in commuter rail systems, like Portland’s Westside Express. “Commuter Rail” is another nebulous and not-always accurate term that I take to mean time-of-day-specific or directional-service rather than frequent, all-day service. North San Diego County’s Sprinter service, which runs DMUs, decribes their operations as “light rail”, and that service has 30 minute headways during commuter hours and hourly service outside of that time. To me, that’s commuter rail, though it sounds like it’s pretty excellent commuter rail. Of course, then I see a photo like the one to the right, of the South Shore Line running down the middle of the street, connected to an overhead wire and I realize there’s are simply too many variables and varieties in the transit world to allow for easy one-world categorization.
So is there an official definition for “light rail”? According to this research paper that chronicles the birth of light rail in America, the term “light rail transit” was introduced in 1972 to describe new North American systems that were modeled after Germany’s “Stadbahn” systems. After the Second World War, European cities were rebuilding their streetcar systems using bigger trains with high floors, more doors, and stream-lined payment. This ended up being a cheap way to upgrade capacity and still provide rapid service. Even before WWII, Boston, San Francisco and Philadelphia both had streetcar systems that ran into subways in their city centers. These systems are now usually called light rail, or sometimes, pre-metro, ie a light rail system that runs in tunnels in the center and on the surface elsewhere, like Link.
The first move toward “modern” light rail in North America was in the 1960s when San Francisco was building BART, and planners there decided to try the European model and move the Muni Metro into the BART tunnel on Market Street (more on the history of the San Francisco Muni Metro in this post). The FTA, then called the UMTA, wanted to create a sort of a modern PCC car, and along with engineering giant Parsons-Brinckerhoff wrote a specification for the “Standard Light Rail Vehicle”. San Francisco and Boston took bids for building the SLRV for the Muni Metro and the Green Line, respectively. The only company to submit a bid was a helicopter manufacturer, Boeing Vertol, who built 100 cars for the new Muni Metro, and 150 cars for for the Green Line. The cars were terrible, and have all been completely removed from service, thus ending any hope of a standard description of what “light rail” officially is.
Since then, however many cities across North America have built transit systems and called them “light rail”, starting with Edmonton in 1978, and 20 more following since. Some are entirely at-grade, like San Jose’s
Andy Filer, Ben Schiendelman and Brian Bundridge helped with this post.