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Transit 101: Heavy Rail and Light Rail

Transit 101 is an occasional series that will focus on the history and technology of modern-day public transit systems. The current topic is a primer on the various modes of rail transit.

Part I: Streetcars and Interurbans
Part II: Heavy Rail and Light Rail
Part III: Commuter Rail
Part IV: Intercity Rail and High-Speed Rail

In the first installment of this series, we explored the history and technology of streetcars and interurbans, modes of rail transit that are characterized by relatively light passenger capacities that often travel on city streets shared with pedestrians and other vehicles. While streetcars are ideal as neighborhood circulators and as feeders into other modes of transit, their relatively slow speeds and limited passenger capacity make them less suited for carrying large numbers of people over greater distances within a metropolitan area. For such purposes, longer trains operating on dedicated rights-of-way are used. Such a form of rail travel falls into two broad categories known as light rail and heavy rail, which we will discuss here.

First, some comments about terminology: The terms “light” rail and “heavy” rail do not refer to the rail gauge or the physical weight of the vehicles, but rather to their respective passenger capacity. (Light rail vehicles may actually have a heavier per-axle weight than so-called heavy rail vehicles.) The term “light rail” was coined in 1972 by the Urban Mass Transit Administration (now Federal Transit Administration) to describe a form a rail travel that has a lighter passenger capacity than traditional subway trains. Although the “light rail” term is relatively new, we will find that modern-day light rail transit shares a few notable characteristics with the old interurbans of yore.

The American Public Transit Association defines light rail and heavy rail respectively as follows:

Light Rail is a mode of transit service (also called streetcar, tramway, or trolley) operating passenger rail cars singly (or in short, usually two-car or three-car, trains) on fixed rails in right-of-way that is often separated from other traffic for part or much of the way. Light rail vehicles are typically driven electrically with power being drawn from an overhead electric line via a trolley or a pantograph; driven by an operator on board the vehicle; and may have either high platform loading or low level boarding using steps.

Heavy Rail is a mode of transit service (also called metro, subway, rapid transit, or rapid rail) operating on an electric railway with the capacity for a heavy volume of traffic. It is characterized by high speed and rapid acceleration passenger rail cars operating singly or in multi-car trains on fixed rails; separate rights-of-way from which all other vehicular and foot traffic are excluded; sophisticated signaling, and high platform loading.

(In the United Kingdom, “heavy rail” refers to mainline commuter and intercity trains, which we will explore in future installments of the Transit 101 series.)

It is important to note that these terms are merely broad categories, and there is generally no hard-and-fast rule that makes a firm distinction between light rail and heavy rail. There are a number of rail transit systems throughout the US and the world that adopt a hybrid approach, incorporating certain characteristics of each.

Early Rapid Transit History

The concept of grade-separated rapid transit first arose in London in the mid 1800’s, as a means to connect the city’s multiple railroad terminals to each other and to the central core of the city. The first segment of what would become the London Underground opened in 1863, with the first electrified section beginning operation in 1890. The system has been steadily expanded ever since, incorporating shallow subways built via cut-and-cover as well as deep-bore “Tube” lines, eventually becoming one of the most extensive and well-patronized rapid transit systems in the world.

Electrification played a major role in the spread of rapid transit, particularly in the form of underground subways. London’s first Underground line originally used steam locomotives, but the resulting smoke in the confined space of the tunnels proved dangerous and uncomfortable. Several solutions, including cable cars and pneumatic systems, were attempted, but electric traction technology ultimately proved successful. This allowed electrical power to be generated off-site, and transmitted to the train’s traction motors via third rail or overhead catenary. In 1897, Frank J. Sprague invented multiple-unit train control for use on Chicago’s South Side Elevated Railway, which allowed multiple railcars to be fitted with motors, all controlled from a single motorman’s cab. This eliminated the need for locomotive-hauled trains in rapid transit service.

Rapid transit technology quickly spread around the world. The first subway in the United States, part of what is now the Green Line in Boston, opened in 1897 to separate streetcars from surface traffic, and now operates as a modern light rail system. Although the tunnels are no longer used by heavy rail subway trains, the Main Line Elevated (now the Orange Line) used the tunnels beginning in 1901. (The modern-day Orange Line now runs in its own dedicated tunnels through downtown Boston.)

Photo: Peter Dougherty /

America’s most famous and extensive subway system began as the Interboro Rapid Transit (IRT) Subway in 1904, designed and built by William Barclay Parsons, who founded the firm that would become Parsons-Brinckerhoff, a multinational engineering and construction management firm with projects all over the world, including the Cincinnati Streetcar. The New York City Subway has since been expanded to to include over 229 route miles, 842 track miles, 468 stations, and now serves over five million riders per day.

Other American cities to build rapid transit systems during the pre-war years included Philadelphia, Chicago, and Cleveland, as well as additional lines in Boston. Here in Cincinnati, construction was begun on a rapid transit loop built to similar specifications as what is now Boston’s Red Line, but was abandoned in 1925.

The Post-War Years

The years following World War II saw a dramatic shift in American transportation policy in favor of the automobile, with the Cincinnati subway’s right-of-way commandeered for freeway construction, and most streetcar systems throughout the country being either severely curtailed or, more often, shut down altogether and replaced with diesel-powered buses. Those systems that survived were invariably those that at least partially operated on dedicated, underground rights-of-way where diesel buses cannot travel.

Despite the dominance of the automobile, some rapid transit systems continued to expand. Chicago’s Dearborn Street Subway, now part of the Blue Line, opened in 1951. (That subway is essentially a twin to the earlier State Street Subway, now carrying the Red Line, which opened in 1943.) In Philadelphia, the PATCO Speedline made use of existing infrastructure and new construction to form a new rapid transit line serving southern New Jersey that opened in 1969. PATCO pioneered the use of Automatic Train Operation (ATO), which would become an important component of modern rapid transit systems that would be built in the following years.

The first comprehensive system to the planned and built during the post-war era was the BART (Bay Area Rapid Transit) system serving the San Francisco area. By the time of its inception, the word “subway” had come to conjure up images of filthy, graffiti-covered trains, rampant crime, and dimly-lit stations. BART sought to re-define the idea of public transit in the popular imagination, featuring sleek, fast trains and modern stations. BART’s first segment opened to passenger service in 1972, with its Market Street Subway also featuring tunnels for MUNI light rail vehicles.

This re-envisioning of rapid transit soon took a major leap forward in the nation’s capitol, with the first segment of the Washington Metro beginning operations in 1976. Over the following three decades, Metro has been expanded to include 106 route miles and 86 stations, with further expansions underway. Metro is now the nation’s second-busiest rapid transit system after the New York City subway, serving over 800,000 riders per day. As a result of Metro’s construction, the Washington, DC area now enjoys the nation’s second-highest transit ridership per capita, despite being smaller in size than several other American cities. (Elsewhere in North America, rapid transit systems in Mexico City, Toronto, Montreal, and Vancouver have higher ridership figures per capita.) The Washington Metro is notable for a number of innovations, particularly its use of distinctive architecture as part of its branding and identity, with most of its stations featuring a consistent design by Harry Weese Associates of Chicago. Metro is also known for its zero-tolerance policies against litter and vandalism, making it one of the cleanest rapid transit systems in the country.

Photo: Ben Schumin /

In 1979, Atlanta’s MARTA began rapid transit service with rolling stock similar to that of the Washington Metro. The MARTA system now consists of 48 track miles and 38 stations, serving almost 260,000 riders per day. Several expansion proposals are currently under study.

Smaller heavy rail metro systems have been built as single lines in Baltimore in 1983 and Miami in 1984. Both systems are built to the same technical specifications, allowing them to reduce capital costs by combining their order for rolling stock.

The most recent heavy rail rapid transit system to be built “from scratch” in the United States is the Red Line in Los Angeles, opened in 1993. The Red Line and the newer Purple Line currently serve 155,000 daily riders at 14 stations, with plans for future expansion currently underway. Expansions of existing heavy rail systems currently under construction include the 7 Line Extension and Second Avenue Subway in New York, and the Dulles Airport extension on the Washington Metro.

The Advent of Light Rail

Photo: Krische Construction

Despite the success of post-war metro systems such as BART and the Washington Metro, recent decades have seen scarce federal funding for large-scale transit projects, forcing cities to develop alternate approaches to public transit. The term “light rail” was coined by the Urban Mass Transit Administration in 1972 to describe rail service with lighter capacity than traditional metro systems, operating mostly on surface routes and sometimes in shared street traffic, avoiding the high costs associated with subway construction.

Although the term “light rail” only dates to 1972 and is generally considered a new development in mass transit, several older streetcar systems in the United States now operate as modern light rail systems, including the Green Line in Boston, the MUNI system in San Francisco, and the Subway-Surface Trolleys and Norristown Line in Philadelphia. Light rail may be thought of as the successor to the interurban, which traveled on surface streets within urban areas but usually traveled on their own rights-of-way outside the city.

Photo: Siemens

The earliest modern light rail system in the United States was the San Diego Trolley, which opened in 1981. Technically not a trolley, the San Diego system served as the model for light rail development throughout the country nonetheless. Light Rail in San Diego now consists of three lines totaling 51 miles, serving 53 stations.

Light rail has become the fashionable choice for medium-sized cities seeking the benefits of rail-based mass transit, with over 30 cities in North America operating light rail systems. Los Angeles and Baltimore make extensive use of light rail to compliment their heavy rail metro and commuter rail systems, while Portland, Denver, and Dallas operate substantial stand-alone systems. Recent new-start light rail systems include Charlotte, Houston, Phoenix, and Seattle. Here in the Midwest, St. Louis and Pittsburgh both operate light rail systems that run in subways through their respective downtown business districts.

Recent regional rail plans for Greater Cincinnati, most notably the 2002 Metro Moves plan, have proposed light rail service for the area, including the conversion of the abandoned subway tunnels to light rail use.

Heavy Rail and Light Rail Compared

The following chart summarizes some key differences between the two modes:

Heavy Rail Light Rail
Passenger Capacity per Train / Vehicle Up to 68 seated, 192 total per car.
Up to 544 seated, 1536 per eight-car train.
(Washington Metro 7000-series rolling stock)
Up to 72 seated, 228 per vehicle.
Up to 144 seated, 456 per two-unit consist.
(Siemens S70 rolling stock)
Average System Speed (including dwell time at stations) 28 MPH (Washington Metro) 19.6 MPH (Portland MAX)
Top Speed Between Stations 75 MPH 66 MPH
Right-of-Way Fully-dedicated right-of-way, separate from pedestrians and other vehicles. May be in the form of subway, elevated viaduct, surface alignment, or freeway median. May operate on a fully-dedicated right-of-way, a surface alignment with grade crossings, or on city streets in shared traffic.
Power Supply 600V or 750V DC via third rail 600V 750V DC via overhead catenary
Platform Height High-level platforms, 40″ to 48″ above the rails. May use high-level or low-level platforms, or a combination thereof. Light rail systems with extensive street-running segments generally use low-level platforms, 18″ above the rails.
Fare Collection Fare gates in stations. May use a flat fare (New York City subway) or a zone-based fare system (Washington Metro). Proof-of-payment, with enforcement via random spot checks. Fares may be flat or zone-based.
Construction Cost per Mile $50M – $250M $15M – $100M

(Sources: WMATA 7000-series rolling stock procurement documents, Siemens S70 data sheet, and the Transit Technologies Worksheet at

Note that these are generalities; rail transit systems come in a wide variety of shapes and sizes, and there are a number of American systems that incorporate features of each. For example, the Chicago ‘L’ often runs two-car trains that carry fewer passengers than a Siemens S70 light rail vehicle on Portland’s MAX system, and construction costs of Seattle’s new Central Link tunnel were comparable those of heavy rail subway construction.

This amateur video shows a Washington Metro Red Line train arriving and departing at Union Station in 1996:

This video shows various scenes from Portland’s MAX light rail system:

Heavy rail obviously offers significant advantages over light rail in terms of speed and passenger capacity, but those advantages come at a high cost. We will explore this dilemma in future articles, particularly as it relates to the future of transit in the Greater Cincinnati region.

In the meantime, stay tuned for the next installment of Transit 101, in which we will make the jump from transit to railroads, and explore commuter rail.