Light rail? Heavy rail? Subway? Rail transit modes fall on a continuum

This article was first published on October 21, 2009. It's still useful information, so we're sharing it again, with a few minor updates.

Despite wide variety in transit systems around the world, here in the United States we only have a few words to describe transit modes, such as commuter rail, heavy rail, and light rail.

In my recent counterpoint post on the Silver Line and the viability of a Dulles Express Line using the Washington and Old Dominion Trail, I touched briefly upon the differences between American and European transit concepts. Because we don’t have many words to describe a variety of systems, it can be difficult to compare and constrast different types of transit, especially those in other countries. With so few words, things get lost in translation.

As far as the Federal Transit Administration is concerned we have only a few words to describe our modes. There are certainly more variations on modes than those found in the National Transit Database’s glossary. Instead of a fixed set of modes, transit systems really fall on more of a continuum.

In this graphic, more local modes serving shorter trips, like guideways and streetcars, appear above more regional modes used for longer trips. Even within a group, some systems have a more regional flavor than others. For instance, BART, while still heavy rail, is closer to a regional rail system than is Washington’s Metro. And Los Angeles’ Red and Purple Lines with far less suburban-serving segments are closer to the subways of the pre-auto era.

Spencer Lepler correctly called Metro a hybrid between subways and commuter rail. Since it is a hybrid, it can’t be considered purely a subway or a commuter rail system. But the FTA doesn’t consider the Washington Metro any different (as a mode) from the Boston T or the New York City Subway.

Metro is a modern heavy rail system, while Boston and New York have pre-auto age heavy rail systems. Chicago’s Green Line is quite different from Washington’s Green Line. The root of these differences comes from the market for which each was built. Chicago’s Green Line was built mainly with walk-to-transit riders in mind, while Washington sought to cater to drivers bound for the central business district from the suburbs.

In the comment threads which have sprouted from the various Silver Line posts from last week and this week, many comparisons have been drawn to European systems and systems in other American cities. These other systems are good places to look, because we can gain insight from the variation between modes. Europe is a particularly good place to look to add a little perspective.

Because the distinctions are important, let’s look a little more deeply at nomenclature.

• Streetcars: Streetcars often operate as single units in traffic with curb-side stops. Sometimes they have a semi-exclusive right-of-way, like a median (New Orleans) or private ROW (Mattapan). They often act as feeders to the regional system and mainly serve closer in nieghborhoods. Streetcars are sometimes older systems dating back many years (as with Philadelphia), while modern streetcars are quite in vogue today (as in Portland and Seattle). Other cities have (re)created vintage (San Francisco) or faux-vintage (Charlotte) streetcar lines.
• Light Rail: This mode began appearing in North America in the late 1970s. Light rail offered a cheaper method to create a regional system and have become popular as substitutes to heavy rail. They serve corridors where heavy rail investment is not practical. In some cities, light rail systems take on many of the attributes of heavy rail, including downtown subways (San Francisco, Seattle) and level boarding (Charlotte, St. Louis). Some of these systems were built from scratch and serve as a regional-scale system (Dallas, Portland) while others are direct descendents from streetcar systems that have been upgraded (Pittsburgh).
• Light Metro: I didn't discuss this in the original version of this post, but there are a few Light Metro type systems that are essentially hybrids between Light Rail and Rapid Rail. These systems are entirely grade separated, like Subways and Rapid Rail, but use shorter trains and smaller stations, so have a lower carrying capacity, which is sometimes made up for with higher frequencies. The most well-known example of this is probably Vancouver's SkyTrain. Honolulu is also currently building a Light Metro line.
• Subways: Systems like the New York Subway and the Chicago L are a type of heavy rail. While these types of service are certainly regional in nature, they often serve only the central municipality and not surrounding jurisdictions. Stop spacing is fairly close and speeds are slower than more regional-type services. The defining characteristic of this subset of heavy rail is that ridership is based on walk-to riders rather than drive-to riders.
• Rapid Rail: The modern heavy rail systems constructed in the 1970s, 80s, and 90s were often known as Rapid Rail. In fact, the Rs in BART and MARTA both stand for ‘Rapid’. However the distinction gets a little blurry here. Rapid Rail systems typically serve the metropolitan area as a whole. Like the Washington Metro, surrounding jurisdictions have high levels of service as well. Speeds are faster than on subways and the distance between stops is higher.
• Regional Rail: Regional rail is a subset of FTA’s commuter rail mode. I think of regional rail as different from commuter rail mainly based on service patterns. Regional rail trains, as their name suggests, serve whole regions. They also offer bi-directional and off-peak service in the region. One of the best examples of regional rail is the SEPTA Regional Rail network in Philadelphia. With a center city tunnel based on the S-bahn tunnels in several German cities, the network serves the central city and the suburbs with quick trips. Service frequencies are lower than one would find on Rapid Rail.
• Commuter Rail: Commuter rail, as I pointed out above, typically only offers peak-period, peak-direction service. In the Washington region, VRE and MARC‘s Brunswick Line offer good examples. MARC’s Penn Line, on the other hand, acts more like regional rail.
• Other Modes: The FTA also considers Cable Cars, Inclines, Monorails, and Automated Guideways as rail modes. These tend to serve specialized and smaller markets. Cable cars, for instance, can easily be grouped with streetcars, as they serve similar markets and have similar attributes. Inclines have very limited use, but often serve as vital links within transit systems. Monorails and Automated Guideway systems also tend to serve very localized markets or act as distribution systems. It is possible to build entire systems with these technologies, as is the case with Vancouver’s SkyTrain, but in the United States, they tend to be limited to moving people around central business districts, as is the case in Miami and Detroit.

When comparing American transit modes to those found in Europe, things don’t always translate directly. For instance, while systems like Washington’s Metro or San Francisco’s BART might be thought of as German U-bahns because of their heavy rail designation, they’re actually closer to the S-bahn systems in Berlin and Hamburg and Paris’ RER. Of course, the S-bahn systems in smaller German cities, like Stuttgart and Munich, resemble regional rail.

Looking across the pond can create confusion as well. In London, for instance, the Docklands Light Railway has dramatically improved service to East London. But the system is not light rail in the sense that most American’s think of it. It would be more accurately be described as a Light Metro. FTA would consider it Automated Guideway Transit. The Docklands system, unlike most American light rail systems, is entirely grade separated.

And contributing to the idea that America and Britian are two countries separated by a common language, heavy rail in Britian denotes regional and inter-city trains - not urban subway and rapid rail systems, which is what it means in the United States. Even Dr. Gridlock managed to get that one confused, telling a reader that MARC and VRE are heavy rail. In fact, according to FTA, MARC and VRE are both commuter rail.

But looking across the globe for good examples of transit generally yields greater understanding of the continuum, even if it makes it harder to quantify. Karlsruhe in Germany has a unique system known as the Stadtbahn. The Stadtbahn name in Germany usually denotes light rail-type trains, but in Karlsruhe the transit system is a unique hybrid of light rail and regional rail. In the city center, trains run in street. However, some services merge onto the conventional rail network for direct, rapid services to suburban destinations.

Munich and Stuttgart both have large regional rail (S-bahn) networks which feed into a central tunnel in the urban core. These tunnels have high platforms and essentially act as a central subway bolstered by the high frequencies resulting from the combined lines.

Expanding on this continuum concept, I added short-haul inter-city services, although perhaps a better name for the concept is needed. Amtrak services like the Capitol Corridor in California or Keystone Services in the Mid-Atlantic cater to longer-distance commuters as well as inter-city and inter-region travelers. Additionally, even high-speed services like the Acela offer a quick trip from far-flung suburbs. Joe Biden, for instance, commuted from Wilmington, Delaware daily on the Acela as a Senator.

People often like to put our transit systems in silos, and sometimes people disagree about which silo a particular transit system belongs in (especially in our comment threads). A good example can be to look at four American cities who have upgraded their streetcar systems over the years and one modern system.

In about 1907, Philadelphia opened a subway tunnel for trolleys stretching from City Hall to 40th 22nd Street. The streetcars operated as single cars and required passengers to climb steps to board. Outside of the center city, the cars ran in streets, shared with other traffic. Boston had a nearly identical setup for their trolley subway, which opened in 1897. Over on the west coast, San Francisco's remaining streetcar lines all converged on Market Street and ran at street level through the Financial District until 1980, when the Market Street Subway's upper level opened.

In Philadelphia, the PCC streetcars that had been operating through the trolley subway were replaced by modern vehicles in 1981. These modern vehicles still operate as single cars, and are essentially the same length as a PCC streetcar. and require patrons to climb steps. Even at some of the subway stations, fares are collected on board, rather than via faregates. In Boston, the trolley subway is now known as the Green Line.

In 1976, modern vehicles began to replace the PCC streetcars. These vehicles were longer and articulated, though they still required stepwells for boarding. Fare payment in the subway takes place at faregates in the station allowing for all-door boarding, but riders pay the driver when boarding on the surface portions. The Green Line operates with trains coupled together in sets of up to two cars.

In San Francisco, on the other hand, the opening of the Market Street Subway coincided with the introduction of modern vehicles, replacing the PCC cars. These trains can operate in sets of up to 3 cars and have level boarding in the subway, and at some other stations on the surface, and with proof-of-payment, all-door boarding takes place throughout the system.

So, these three cities went in different directions. Are they all the same mode? Or are two light rail while the other is a streetcar? Or vice-versa? If we take the continuum view, Philadelphia's Subway-Surface lines are definitely the most like a streetcar, while the Muni Metro is the most like a light rail?

What about St. Louis's Metrolink and Pittsburgh's T? They both use the same vehicles, and both operate them in trains of up to 2 cars. Both have a downtown subway. In St. Louis, Metrolink was built from scratch, opening in 1993. In Pittsburgh, the T was converted from a streetcar system in the 1980s, with modern vehicles running starting in 1984 and the subway opening in 1985. Pittsburgh still uses a mix of level, all-door boarding at some stations, and front-door-only stepwell boarding at others. St. Louis is entirely all-door, level boarding. How do these systems compare with each other? How do they compare with the Philadelphia, Boston, and San Francisco examples?

We need to focus less on a rigid structure for naming rail modes. Individual systems possess a richer set attributes beyond just their FTA mode. Thinking of transit systems as lying somewhere on a continuum may help us find better ways of comparing systems across regions and nations.