Route 48 and Central Link
48 and Link, photo by Oran

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 South Shore Line running in Michigan City
The South Shore Line running in Michigan City, from wikipedia

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 and San Diego’s, and some have significant underground sections, like Pittsburgh’s, Edmonton’s and, eventually, ours. So while there’s no set-in-stone definition for light rail, there are already a quite a few systems, with more coming on line all the time.

Andy Filer, Ben Schiendelman and Brian Bundridge helped with this post.

36 Replies to “What is Light Rail?”

  1. From my perspective, Andrew has hit the nail on the head.
    “Generally “light rail” is used to describe systems that are somewhere in the middle…”
    Link is a good example of a typical crossover light rail system. Electric powered, dedicated ROW, multiple car trainsets, traveling 55 mph, with short headways all day passes the ‘duck test’ for heavy rail.
    Run the same trains down MLK, with slower speeds, multiple stations and that’s pretty much like most other light rail systems, and some streetcars. Rename the same cars, rail, and overhead power, with very close stops, mixed traffic, and it’s a streetcar.
    Now, remove the overhead wire, and self propel the electric motors with an on-board diesel engine, and presto.. it’s a DMU. If the tracks are shared with freight trains, and generally run during typical commute hours, it passed the test for commuter rail. Keep going to Olympia, and it’s intercity rail. Go over 79 mph, and it’s HSR.
    Maddening!, isn’t it?

    1. Over 79 is not HSR. The FRA defines 90 mph as HSR, but that’s certainly not the case overseas. BART, for instance hits 80, as do many amtrak lines. Only the Acela is considered HSR.

      I do wish you would stop misleading people by telling them that washington “has been implementing HSR for the last 10 years.”

    2. I don’t agree that going to Olympia is intercity rail, Olympia is part of the Seattle-Tacoma-Olympia Combined Statistical Area. But the best definition I’ve seen for light rail is rail that has the ability to run in mixed traffic.

  2. If you want to understand the distinctions even better, check out Vukan Vuchic’s book “Urban Transit Systems and Technology”.

  3. The fuzziness of these terms and public’s confusion about them leads to some interesting situations. Here in Phoenix, we’ve just opened our 20-mile light rail line. Ridership is high and even some skeptics are beginning to admit it’s a good thing. What’s funny, though, is that at least half the people I talk to mispronounce the phrase. They put the emphasis on the first word rather than the second, making it sound like a rail made of light rather than rail transit with light infrastructure. Also, now that light rail is proving popular here, people want more of it, leading for calls for “light rail between Phoenix and Tucson.” Actually, you can’t really have light rail for intercity transport over a 100-mile distance. That’s better suited to commuter rail, but I think the distinctions noted in the post are lost on many who are new to rail of any type.

    1. That’s definitely an issue, and I’m sure I made a lot of assumptions on familarity with some system or another. But how can you make comparisons if you have no reference to make comparisons with?

    2. It would also be ridiculously expensive – LRT is even more expensive than Maglev on a per mile basis!

      Obviously, running rail through a flat desert would be less expensive, but it does put things in perspective a bit. Considering there already is a rail line linking PHX and TUC, all they need are trains, right?

      1. Maybe. The problem is that when commuter trains run on existing freight lines, they sometimes take second priority to freight and therefore run at slow speeds with unpredictable operations. To be honest, though, I’m hardly an expert on commuter rail. My point was more that to a portion of the public, any train is “light rail.” Some people seem to think “light rail” is a new term for all rail transport, rather than a specific kind of rail transport.

  4. Minor typo: Edmonton, not Edmondton.

    Interestingly, SkyTrain in Vancouver is described as Light Rail, despite being completely grade separated (which is required because of the ALRT propulsion) and operating at speeds comparable to a subway.

    1. Fixed the typo.

      The NYC subway is way slow through Manhattan, averaging like 25mph over the whole system, and much less than that in the city. That’ll be comparable to link for the most part.

      1. Until a couple of weeks ago, South Ferry station had about the same capacity as, say, Westlake, too. :)

    2. I believe they use the term light metrorail for the Vancouver System. It is truely a cross-over, and the only major system like it in North America (seeveral in Asia). It is more similar to a metro or rapid-rail vehilce and operation, but with a light-rail size (narrow cars, and short consist). The nice thing about fully automated operation, a 2 car train every 3 min is the same price as a 4 car every 6 min – I love not having to wait.

  5. I thought systems such as BART, NY Subway, DC Metro, and others similar were considered “heavy rail,” which is what Seattle would have had if they had been smart enough and voted for it in 1968.

    Then, is the Atlanta system “light” or “heavy” rail?

    1. Atlanta’s rail system, MARTA, is like BART and the DC Metro and it even opened in a similar time frame. Seattle would have had that sort of system.
      Maybe you misread the sentance, but all of those systems are generally considered “heavy” rail.

      1. I think I misundertood what you meant by the word spectrum.

        When you say, “on the low end of the spectrum…. and on the high end ….”
        I thought the word spectrum meant for light rail only rather than entire spectrum on rail.

        Thanks for the clarification.

  6. “Some are entirely at-grade, like San Jose’s and San Diego’s”

    A brief correction, the San Diego Trolley (light rail) has an honest to goodness underground “subway” station at the San Diego State University (SDSU) stop, see link below for photos. The green line also travels on an elevated, grade separated section through a good portion of Mission Valley.

    1. As you note, in San Diego, they call their light rail system the Trolley, which perhaps then allows them to call their DMU line “light rail.”

      Somebody once described the origin of the term light rail as “rail transit done light”; light in the sense of smaller footprint, lower cost, less “intense.”

  7. The excellent Skehan post also mentioned service design; its not just hardware. In Ottawa and New Jersey, there are DMU lines that provide two-way 15-minute headway service, so it is a LRT-type service rather than a commuter rail service (more one-way and more peaked). In an earlier chain, STB discussed Link characteristics; with long station spacing, it tilts toward a BART-type service pattern as opposed to a TriMet LRT with more stations. Between Northgate and Mt. Baker, Link LRT is like Metro-lite.

    1. I think that Link most closely resembles the Stadtbahn systems in Germany. Many of them were built with underground sections through the city center and then at-grade alignments in the periphery. These systems have a great variety of alignment types that are typical of light rail.

      If you look at Frankfurt

      or Essen

      you’ll see many of the features of Link and many of the features that come to mind when thinking of light rail.

    2. However, doesn’t BART and DC’s METRO run a system with an automatic train control system? I don’t think Seattle has that kind of signaling and control system, right?

      There are a lot of infrastructure, train types, and control systems that kind of define the different types of services – commuter rail/streetcar/light rail/heavy rail (metro) systems. Grade separation, capacity, and frequency are also pretty important.

      Don’t forget that London’s Underground and the NYC Subways started out using steam trains.

    3. Link has Automatic Train Protection which prevents the train from overspeeding. The speedometer shows the current speed and the speed limit. If the train passes a stop signal or exceeds the permitted speed, brakes are automatically applied.

  8. I would say that the interest here is more in what is not defined than in what is.

    Suggest a future trolley route on this blog and you’ll immediately hear howls of outrage that “That should be a light-rail route!”

    What’s the difference? High platform or low platform, street-running or grade-separated ROW, single-car or multi-car, the distance between stops, or the type of signaling employed…they all add up to a definite impression in the reader’s mind that may or may not be relevant to the growth of a system over a period of many years.

    The real news is the versatility of modern light-rail equipment. You can run it in the street or a tunnel, carry cargo, go fast in open countryside- etc etc.

    In this case the public is correct in vaguely assuming that something that’s not too big and not too small is…light rail.

  9. This posting reminds me of a major pet peeve I have with Sound Transit. For all the variable electronic information signs and static information signs, including wayfinding signs (like those in the downtown tunnel), Sound Transit has been using the words “Link Light Rail”. This really bothers me. The brand of the rail service is “Link”, not “Link Light Rail”. Can you please put pressure on Sound Transit to stop using “Link Light Rail” on those signs and any other passenger information? Interestingly, Sound Transit always uses “Sounder” and not “Sounder Commuter Rail” in its passenger information.

  10. I’ve always seen “light rail” and “heavy rail” used in terms of capacity. It’s certainly not the weight of the cars themselves which determine the naming, nor is it the propulsion method.

    Generally the term “Light rail” is a marketing usage to imply “light impact” which it is not when it’s in the street or on a concrete elevated track, “light cost” again not cheap when elevated or tunneled, but rarely is it bandied about for it’s original meaning of “light capacity.”

    Whether Seattle should have built a “Heavy rail” system like the one in Atlanta is a much more interesting topic. As far as who pays for the cost, it would have been a total win to have the Fed’s picking up the tab. As for getting the growth in the region to build around the stations before all the farms were gone, another big win.

    Or should have Seattle built the Monorail system out that was started at the World’s fair? Elevated everywhere, as heavy capacity as the current Light rail system.

    Both of these systems would have had trouble with the floating bridges of the 60’s though. But IMO either would have been better than what we got which was nothing.

    1. Yeah, former Gov. Rossellini told us if he had been re-elected one of his policy ideas would have been to expand the Seattle Center Monorail to the airport.

      *SHRUG* Who knows if he would have been successful, considering how Sound Move fared… but could you imagine if we had that kind of spine up and running for 30+ years?

  11. I think the places where DMUs are classified as light rail are because the FTA classifies any DMUs other than Colorado Railcar’s as light rail, and they can’t be used in conjunction with freight or Amtrak

  12. My friend went into a bar and ordered a martini.

    “Would you like Stoli or Absolut?” the bartender asked.

    “Neither. I asked for a MARTINI.” my friend responded. “That’s a vodka martini.”

    “Well, that’s what people around here mean when they order a martini.”

    Unbelievable? Perhaps. A martini never used to mean a drink with vodka. It meant gin and vermouth. And an olive. Nowadays, you can order an apple martini, or a chocolate martini, or any number of abominations that use the word martini and yet are NOT a martini! The same thing happened with the “Cocktail.” That used to be a specific drink. These days it is a generic term for any mixed drink.

    My point with this long story is that sometimes the public, not the experts, or the fan boys, get to name something, simply by everday usage, even if that usage is technically WRONG. So, maybe light rail does mean any passenger rail that’s not a subway or an Amtrak train.

  13. The effort to call DMUs ‘light rail’ is largely an attempt to co-opt positive brand identity painfully built over the last couple of decades by major-league operations like Portland’s. Unfortunately, it’s succeeded with some – leading to ridiculous claim’s like Austin’s (no new track; no ability to actually run in the urban core because the vehicles can’t corner; but because we bought a new diesel train and put it on existing tracks it’s somehow now ‘light rail’?)

    1. Some DMUs are in fact LRVs in the sense that they are diesel powered versions of vehicles widely recognized as LRVs. See for example the Stadler DMUs used by the NJ River line which are capable of street running.

      To further the confusion there are tram-trains which are designed to operate as street trams, Stadtbahn or pre-metro, and commuter trains on mainline rail lines.

      I think the reason modern European low-floor versions of the Budd RDC get called “light rail” is because they don’t meet FRA requirements and therefore need to be separated from Freight movements. Because in all other respects the Desiro and Talent walk and squawk more like mainline rail vehicles.

      1. The NJ River Line only did ‘street running’ by condemning wide swaths of land; check out the turns it ‘makes’ on google or another mapping tool sometime. They are most definitely not anything like what most people would consider an urban rail vehicle.

        The conclusion in Austin with similar vehicles was that we couldn’t get any farther into town; could basically never get to UT or the Capitol; etc.; all of which were possible with normal LRVs.

      2. Well the Stadler vehicles have a smaller turn radius than the Talent or Desiro DMUs.

        The “tram-trains” are more LRV like.

  14. Remember, it has to cater to LOOTers and run past Section 8 housing.

    Or was it Algona? I forget…

  15. First off, love the blog. I just found it, and I’m loving the articles i’m seeing.

    Secondly, a definition for you of Light Rail. I read most of the article and skimmed the comments, so I’ll apologize if this was already made clear, but my understanding is that light rail is anything that doesn’t meet the Federal Railway Administration’s weight requirements for operating on freight lines.

    Many probably already know this, but the FRA requires that all trains are at least a certain weight (i think it’s around 80 tons per car) so that if they collide with another train they’ll have enough mass to survive a crash with a freight train (avoiding a sledge hammer vs. aluminum can situation). Amtrak passenger cars meet the FRA guidelines, which is one reason they’re very slow. One thing that hamstrung the Acela project is that it’s operating on normal tracks for much of its run, so it was required to meet the FRA weight guidelines. Similar aged high speed trains that operate in Europe (Acela was built by Alstom, builder of France’s TGV) are almost half the weight, which allows them to easily reach the 200 MPH operating speeds they do. Of course, the other reason it’s so slow is that much of the system is shared with older commuter rail, which is legally limited to 79 mph (by the FRA), as well as being too tightly curved for high speed operation. But, i digress.

    Light rail isn’t an indication of passenger load, or of impact to the environment or anything else. Technically the NYC subway, BART, the SLUT, portland’s MAX and Vancouver’s Skytrain are all light rail EMU’s.

    I believe the Link Light Rail is being called that because it operates elevated, on the surface, and in tunnels, so calling it the Seattle Subway or Seattle El would be inaccurate.

    1. By extension, DMU’s that don’t meet the weight requirement would technically be light rail. Light rail accelerates and stops more quickly than does heavy rail, so even though the DMU isn’t doing the environment any favors because it’s still burning gas, it should improve train performance. If that improved performance got more people out of their cars and into these trains, the net would be positive. So let’s don’t turn up our noses at improvement to passenger rail service, no matter how imperfect it might be.

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