Light rail, also called light rail transit (LRT), is a type of passenger transportation that uses trains based on tram technology. These trains also have some features similar to heavy rapid transit systems.

The term "light rail" was first used in 1972 in the United States as an English version of the German word "Stadtbahn," which means "city railroad." In the United States, light rail mainly uses special tracks that are not shared with other traffic. These trains can be made up of single tramcars or multiple connected cars. They have lower carrying capacity and speed compared to long heavy rail passenger trains or rapid transit systems.

In a narrow definition, light rail uses trains similar to traditional trams but operates with higher capacity and speed, often on special tracks. In a broader sense, light rail can include tram-like operations that run mostly on city streets. Some light rail systems have features closer to rapid transit. When these systems are completely separated from other roads and railways by being built above or below them, they are called light metros or light rail rapid transit (LRRT).

Terminology

The term "light rail" was first used in 1972 by the U.S. Urban Mass Transportation Administration (UMTA, which later became the Federal Transit Administration) to describe updated streetcar systems in Europe and North America.

In Germany, this type of system was called "Stadtbahn," meaning "city rail." However, UMTA chose the term "light rail" instead. The word "light" refers to the system’s lower infrastructure and capacity needs compared to heavy rail, not its physical weight. How a system is classified depends on the type of track it uses.

The American Public Transportation Association (APTA) defines light rail as follows:

In other countries, "light rail" usually describes newer tram or streetcar systems. These systems can range from those that share roads with cars to those with some tracks that are separated from roads. People movers typically carry fewer passengers than light rail. Monorails and automated guideway systems are different technologies used for specific purposes.

Light rail is not the same as the British English term "light railway," which refers to lightly regulated, low-speed railways.

The term "light rail" helps avoid confusion from different regional terms. For example, in the UK, Australia, Ireland, and New Zealand, "tram" refers to a street-running rail vehicle. In North America, "tram" can also mean an aerial tramway or a land train in amusement parks. Similarly, "trolley" means "streetcar" in North America.

In North America, "streetcar" often refers to older vehicles that share roads with cars, while "light rail" describes newer systems that mostly use dedicated tracks. The term "street railway" (with vehicles called "streetcars") was used in the 19th century, inspired by the German word "Straßenbahn," meaning "street railway." After World War II, Britain stopped most of its tram systems, but many North American cities, such as Toronto, Boston, Philadelphia, San Francisco, Pittsburgh, Newark, Cleveland, and New Orleans, kept theirs. These cities later used the term "light rail" when modern systems were added next to older streetcars. Since the 1980s, Portland, Oregon, has developed all three types: light rail, streetcars, and aerial trams.

"heavy rail" refers to systems with higher capacity and speed, such as the London Underground or New York City Subway. Regular passenger and freight railways are also classified as heavy rail. The main difference is that light rail vehicles can operate in traffic when needed, while heavy rail systems usually use separate tracks.

History

In the late 1800s, some cities began building underground tramways to reduce traffic. Early examples include the Murray Hill Tunnel in New York, used for streetcars in 1870, Marseille's Noailles station in 1893, and Boston's Tremont Street subway in 1897, which was the first subway built specifically for trams in North America and became part of today's MBTA Green Line. London's Kingsway tramway subway opened in 1906 to connect tram networks and operated until 1952.

The "Shaker Heights Rapid Transit" in Cleveland, built in the 1920s, was an early example of a suburban rail line adapted for tram use and is now part of the RTA Rapid Transit. In Europe, a suburban railway in The Hague was converted to tram use in 1927, and in Boston, the Highland branch was converted in 1959 to create the Green Line D branch, which increased ridership with modern PCC cars. In 1964, Chicago's experimental Skokie Swift demonstrated features later used by many U.S. light rail systems.

Many traditional tram and streetcar systems in the United Kingdom, United States, and other countries were shut down after the 1950s because investment shifted to cars and buses. Leeds and Glasgow briefly built modernized tram lines in the 1940s, but by 1962, Britain had stopped using all tramways except in Blackpool. Modern light rail developed mainly in postwar West Germany, where tram networks were upgraded instead of abandoned. These Stadtbahn systems included high-capacity vehicles, dedicated tracks, and underground tunnels in city centers. Except for Hamburg, most large and medium-sized German cities kept their trams and improved them into light rail. Similar upgrades happened in cities like Zurich, Rotterdam, The Hague, Gothenburg, Brussels, and Ostrava in Central and Eastern Europe.

In the United States, planner H. Dean Quinby introduced the idea of a "limited tramway" in 1962, which differed from traditional streetcars by using longer vehicles, multiple doors, and higher passenger capacity. The term "light rail transit" was first used in North America in 1972 to describe these improved systems. The first new system opened in 1978 in Edmonton, Alberta, using German Siemens-Duewag U2 vehicles, followed by Calgary and San Diego. These systems were successful and inspired many others in the U.S., Canada, and Mexico.

From the 1980s onward, light rail and modern trams expanded globally. In Europe, cities that had stopped using trams, such as Nantes (1985), Grenoble, Paris, Strasbourg, Bordeaux, Dublin, Barcelona, and Bergen, reopened tram networks. In Britain, modern light rail returned with the Tyne and Wear Metro (1980), Manchester Metrolink (1992), South Yorkshire Supertram (1994), and Edinburgh Trams (2014).

In North America, the San Diego Trolley (1981) became a model for future projects, and the number of U.S. systems nearly doubled between the 1990s and 2010s, with expansions in Portland, Los Angeles, Denver, Dallas, Minneapolis, and Seattle. Canada added the Ion in Waterloo and the Confederation Line in Ottawa (both 2019), while Australia introduced the Sydney Light Rail in 1997.

In Asia, Japan opened the Toyama Light Rail in 2006, its first new tramway in decades. Light rail systems also started in Chinese cities like Shenyang, Nanjing, Guangzhou, Beijing, and Shanghai.

In Africa and the Middle East, new light rail systems were built in Tunis (1985), Rabat (2011), Algiers (2011), Jerusalem (2011), Casablanca (2012), Dubai (2014), Addis Ababa (2015), and Lusail (2022).

In South America, projects included the Ayacucho Tram in Medellín (2016) and the VLT Carioca in Rio de Janeiro (2016).

Types

It can be difficult to tell light rail apart from other types of urban and commuter rail. A system called light rail in one city might be called a streetcar or tram in another. On the other hand, some lines named light rail are very similar to rapid transit systems. In recent years, new terms like "light metro" have been used to describe systems that carry a medium number of passengers. Some diesel light rail systems, such as Sprinter, are not much like urban rail and could instead be called commuter rail with lightweight trains.

In the past, what is now called light rail operated on heavy rail tracks in the United States, especially with interurban streetcars. An example is the Lehigh Valley Transit trains that ran on the Philadelphia and Western Railroad high-speed third rail line, now known as the Norristown High-Speed Line.

Light rail corridors can be fully separated from other traffic, have a dedicated path on a street, share a street with other vehicles, share space with other public transport, or share space with pedestrians. This gives light rail more flexibility than heavy rail.

Many systems have a mix of features. With good engineering, a rail line can run along a street, then go underground, and then travel on an elevated track. For example, the Los Angeles Metro Rail's A Line has parts that could be called a tramway, light metro, or, in a narrow way, rapid transit. This is common in the United States, where people often do not clearly see the differences between types of urban rail systems.

The hardest distinction to make is between low-floor light rail and streetcars or trams. These systems often use similar technology, and streetcars or trams are sometimes considered a type of light rail. However, some differences exist. Low-floor light rail lines usually have a reserved path and priority at intersections, avoiding mixed traffic to allow faster speeds. Light rail lines tend to have fewer stops and longer routes than trams. Light rail cars are often connected in groups of two to four cars.

Light rail systems can also have features of rapid transit systems, such as underground sections in city centers, as seen in San Francisco and Seattle. These partially separated systems are sometimes called "semi-metros." This type of light rail began when Boston opened its first subway in 1897 and became popular again in Europe from the 1950s. Advances in low-floor and catenary-free tram technology allow for mixed systems with short underground sections, as these require less height than traditional light rail vehicles.

Light rail can be designed to fill a gap between mainline rail and bus services, carrying many passengers quickly and cheaply. In Germany, around Karlsruhe, Kassel, and Saarbrücken, dual-voltage light rail trains use mainline railroad tracks, sharing them with mainline trains. This lets commuters travel directly to city centers without switching to a tram. In France, similar systems are used in Paris, Mulhouse, and Strasbourg, with more plans in development. In 2022, Spain opened the Cádiz TramBahia, where trams share tracks with commuter and long-distance trains from the city's main station. Some challenges in these systems include:

• matching safety systems
• ensuring track power matches the power used by vehicles (often different voltages, rarely third rail vs. overhead wires)
• matching vehicle width to platform positions
• matching platform height

In some cases, tram-trains use old or lightly used heavy rail lines instead of active mainline tracks, like the Manchester Metrolink. In San Diego, the San Diego and Arizona Eastern Railway helped create the initial part of the San Diego Trolley light rail network. In the Netherlands, this idea was first used on the RijnGouweLijn and later on the RandstadRail project.

Many light rail systems—even older ones—have both on-street and off-street sections. In some countries, especially in Europe, only systems with off-street sections are called light rail, while trams on mixed paths are not. However, the requirement for a system to be "separated" can be very basic—sometimes just concrete barriers to stop cars from entering the tracks are enough. Some systems, like Seattle's Link, had on-street sections where light rail and buses shared a path but were closed to regular traffic. The Link was changed to full separation in 2019.

Low-floor light rail vehicles have a low floor, making it easier to load passengers from low platforms that are barely raised above street level. High-floor light rail systems also exist, with larger stations.

Reference speeds from major light rail systems, including station stop times, are shown below.

However, a low top speed is not always a key difference between light rail and other systems. For example, Siemens S70 light rail vehicles used in the Houston METRORail and other North American systems can reach speeds of 55–71.5 mph (88.51–115.1 km/h), depending on the system. Trains in the all-underground Montreal Metro can only reach a top speed of 72 km/h (44.74 mph). Light rail vehicles in Los Angeles have higher top and average speeds than Montreal Metro or New York City Subway trains.

Infrastructure

Light rail systems function between heavy rapid transit and regular street-level trams. Building costs are usually lower than for metro systems, but creating infrastructure can still be expensive. This often leads to lines being built in stages or completed only partially. Light rail vehicles can often work with existing tram networks, which avoids the need for completely new tracks or train cars. In some cases, multiple surface-level branches are used to increase the capacity of underground or elevated sections.

Light rail systems can be described by the type of track they use and features like power sources and speed. Three main track categories include:

• A: Tracks that are completely separate from roads and sidewalks.
• B: Tracks set aside for trains but have some road crossings.
• C: Tracks that share roads with cars and pedestrians.

Regular trams usually operate on category C, light rail often uses category B with some category A sections, and rapid transit typically runs entirely on category A.

Tracks that are separated from roads are called grade-separated and are fully independent. Reserved tracks may be used only by trains or shared with other vehicles. Light rail that runs entirely on independent tracks is sometimes called light rail rapid transit. Some tracks are built to work like regular metro or rapid transit lines. A key difference from rapid transit is that light rail may only have one or a few sections in tunnels or on elevated tracks.

Light rail systems historically used different track widths, with narrow tracks common in the past. Most modern systems use standard track width, which allows standard maintenance tools, easier movement of train cars, sharper turns with connected cars, and better access for passengers. For example, the Tren de la Costa in Greater Buenos Aires changed from wide tracks to standard tracks to use light rail vehicles.

Most light rail systems use overhead wires for electricity, which avoids dangers from electrified tracks on the ground. Some systems use batteries for sections without overhead wires, while a few use diesel power.

Conduit power, which uses electricity through underground tracks, was an early option in cities that banned overhead wires. It was used in London, Paris, Berlin, Marseille, Budapest, Prague, New York City, and Washington, D.C.

In Bordeaux, the tram system uses ground-level electricity tracks in the city center. These tracks are only active under the trams for safety. Outside the city center, trams use overhead wires. This system costs three times more than regular overhead wiring and has high maintenance costs, but it is popular and carries up to 190,000 passengers daily. Sydney, Australia, uses a similar system on two of its tram lines.

Automatic train operation (ATO) tracks where trains are monitored for safety and efficiency. It is used in some light rail networks.

Rolling stock

Light rail routes are run using regular trams (which may have low floors or not) or special tramcars called light rail vehicles, such as the Stadtbahn-car 'type B'. Many light rail systems, including those in the United States, use larger and heavier vehicles than those found on streetcar systems.

The BART railcar shown in the chart is not considered a "light rail" vehicle (it is a heavy rail vehicle) and is only included in the chart for comparison purposes.

Related types of rail transit

Premetro is similar to light rail, which is a type of public transportation where trams travel partly on tracks that are separated from other traffic, such as tunnels or elevated structures. The main difference is that premetro systems are built with the goal of eventually switching to full metro trains. These systems are often developed from existing tram networks. A well-known example is the premetro in Brussels, where some lines have already been or will be changed into full metro lines.

The U-Stadtbahn is another type of transportation that lies between metro and tram systems. It began in Germany and uses existing tram networks. Special trams run underground in city centers. U-Stadtbahn lines can be grouped based on the type of trains used:

• Some lines use large trams (2.65 meters wide) with long train cars, such as in Cologne, Frankfurt, and Stuttgart.
• Other lines used smaller trams with shorter train cars at first, like in Hannover (TW6000) and Bielefeld (Düwag M/N).
• Starting in the late 20th century, some lines began using low-floor trams, such as in Dortmund (U43 & U44), Düsseldorf (Wehrhahnlinie), and Cologne (Lines 1, 7, 9, 12, and 15).

Some systems, like the AirTrain JFK in New York City, the DLR in London, and the Kelana Jaya Line in Kuala Lumpur, do not require a train operator. The Vancouver SkyTrain was one of the first to use driverless trains, while the Toronto Scarborough rapid transit used the same type of trains but had drivers. These systems are usually not classified as light rail but as light metro systems, which are a mix of light rail and rapid transit.

In the United States, interurban-style services are rare because the Federal Railroad Administration (FRA) does not allow non-compliant railcars (such as light rail or rapid transit vehicles) to share tracks with standard freight or passenger trains for safety reasons.

Exceptions, called hybrid rail in the U.S., include NJ Transit’s River Line between Camden and Trenton and the North County Transit District’s (NCTD) Sprinter service in northern San Diego County, California. These systems operate under special permits that allow passenger trains to run during the day and freight trains at night, with time gaps between them. These systems use lightweight diesel-powered trains designed for mainline railroads.

The word "light" in "light rail" refers to the system’s lower capacity compared to heavy rail or rapid transit. However, in "very light rail," the term refers to the trains being lightweight. An example is the British Rail Class 139 train, which operates on the Stourbridge Town branch line.

Very Light Rail systems in the UK use prefabricated tracks and onboard power (without overhead lines). These systems aim to cost about £10 million per kilometer, compared to traditional tram systems and overhead lines, which cost £20–£30 million per kilometer. Testing in Coventry began in 2025, with a full line expected to open by 2027.

Light rail systems (LRT) have the most flexibility in design, engineering, and operations because they can use a variety of track types and control technologies. The challenge is to create efficient, comfortable service without overdesigning systems, which can lead to unnecessary high costs.

Capacity

A single light rail line (needing a space of 7.6 meters [25 feet]) can carry up to eight times more people than a 3.7-meter (12-foot) freeway lane during busy times. Freeway lanes usually reach their limit at about 2,000 vehicles per hour. Beyond this, traffic slows down and becomes difficult to move. With an average of 1.5 people per car, freeways can carry about 3,000 passengers per lane per hour. High-occupancy vehicle (HOV) lanes and ride-sharing can help increase this number, but many areas choose to expand road space instead. This sometimes makes traffic worse, as seen in the Downs–Thomson paradox and Braess's paradox.

By comparison, light rail trains that run on two-track spaces as narrow as two car lanes can carry more than 20,000 passengers per hour in one direction. With moving block signaling, this number can rise to over 25,000.

The number of people a road can carry depends on the types of vehicles allowed. A typical car-only lane can move about 1,900 passenger cars per hour (pcplph). Adding buses or light rail increases this capacity, as shown below:

Bus rapid transit (BRT) is often compared with light rail in planning. BRT in dedicated lanes can carry more than 30,000 passengers per hour in one direction, as seen in Guangzhou’s BRT, which moves up to 350 buses per hour. This requires large stations, priority for buses at intersections, and lanes for faster services. BRT usually costs more because each bus needs a driver and most use non-electric vehicles. Ride quality is also lower, with more sudden stops and starts compared to rail.

Most U.S. light rail systems are limited by demand and carry fewer than 4,000 passengers per hour in one direction. However, Boston and San Francisco reach 9,600 and 13,100 passengers per hour, respectively. Calgary’s C-Train and Mexico’s Metrorrey have higher passenger numbers. The Manila Light Rail Transit System carries more than 40,000 passengers per hour in one direction, using four-car trains with up to 1,350 passengers each. This system operates 30 trains per hour and is fully grade-separated, meaning it is separated from other traffic, like on a bridge or underground.

Costs and efficiency

Light rail construction costs can be very different based on whether tunnels or elevated structures are needed. A study of North American projects found that most systems cost between $15 million and $100 million per mile, with an average of $35 million per mile (except for Seattle). Seattle's Link Light Rail cost $179 million per mile because of tunneling, elevated sections, and deep stations. In contrast, systems in Baltimore, Camden, Sacramento, and Salt Lake City cost less than $20 million per mile.

Freeway lane expansions typically cost about $2.3 million per lane-mile, but these are often built in cheaper suburban or rural areas. The most expensive U.S. road project, Boston's Big Dig, reached $200 million per lane-mile. A light rail track can carry up to 20,000 passengers per hour, compared to 2,000–2,200 vehicles per freeway lane. In Boston and San Francisco, light rail lines carried 9,600 and 13,100 passengers during peak hours, respectively.

Projects that combine highway and light rail improvements can reduce costs. Denver's Transportation Expansion Project rebuilt 17 miles of highway and added 19 miles of light rail for $1.67 billion. This cost $19.3 million per highway lane-mile and $27.6 million per rail mile. The project was completed under budget and nearly two years early.

Calgary's CTrain kept costs low by avoiding tunnels and elevated sections, using existing rail corridors, and combining construction with freeway projects. Its initial cost was $24 million per mile, about one-third of the San Diego Trolley's cost. By 2009, Calgary's system carried three times as many passengers as San Diego's, with lower initial and operating costs per passenger. Operating costs average about C$163 per train-hour, or about 27 cents per ride, compared to $1.50 for buses.

Light rail often has lower labor costs per passenger mile than buses and attracts more riders. It also moves passengers faster with fewer vehicles. Light rail vehicles cost more upfront but last longer, reducing costs over time. Compared to heavy rail, light rail has lower initial costs but higher operating costs.

Light rail is estimated to be energy efficient, with about 120 passenger-miles per gallon of fuel equivalent. However, this efficiency can vary depending on the situation.

Effects

A study of data from the 505-page National Transportation Statistics report published by the US Department of Transportation shows that more people die in light rail accidents than in any other type of transportation except motorcycle travel. Light rail has 31.5 deaths for every 100 million miles traveled.

The same report also states:

Studies have found that light rail can affect health in several ways. Research shows that light rail can encourage more walking and reduce obesity. Additionally, one electric light rail train produces nearly 99 percent less carbon monoxide and hydrocarbon emissions per mile than one car does.

Examples

Around 400 cities worldwide have one or more tram or light rail systems. Some systems were built in the 19th century, and by the 1930s, nearly 900 tram or light rail systems existed. Many of these systems were shut down during the mid-20th century, except in most Central and Eastern European countries. Some cities that closed their streetcar networks have since rebuilt or are rebuilding parts of their former systems.

• An underground light rail station in Edmonton, Canada, which was the first light rail system in North America
• A light-rail vehicle on Hämeenkatu street in Tampere
• The Metrotram in Kryvyi Rih, Ukraine, was taken off the streets but later reconnected to the existing tram network
• A light-rail vehicle of the Changchun Rail Transit in Changchun, China
• A metro light rail station in Porto in 2022
• The light rail in Tunis, Tunisia, was the first light rail system in Africa
• An underground light rail stop in Zurich in 2022
• A tram in Dubai, UAE
• A light rail station in Frankfurt U-Bahn in 1970
• A tramway subway portal in Rouen in 2015
• An underground station in Poznań in 2019
• An underground station in Istanbul in 2020
• A light-rail vehicle of the VLT Carioca in Rio de Janeiro, Brazil
• A Danhai elevated station in 2018
• Light rail in Wuhan