For specific light rail systems, many of which use the words "light rail" as part of their name, see List of light-rail transit systems.
Light rail or light rail transit (LRT) is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than street-running tram systems. The term is typically used to refer to rail systems with rapid transit-style features that usually use electric rail cars operating mostly in private rights-of-way separated from other traffic but sometimes, if necessary, mixed with other traffic in city streets. Modern light rail technology is highly flexible in how it can be used, and whether any given system is considered a true rapid transit system or not depends on its implementation.   
See also: Passenger rail terminology. The term light rail was devised in 1972 by the U.S. Urban Mass Transportation Administration (UMTA) to describe new streetcar transformations which were taking place in Europe and the United States. In Germany the term stadtbahn was used to describe the concept, and many in the UMTA (now called the Federal Transportation Admistration) wanted to adopt the direct translation, which is city rail. However, the UMTA finally adopted the term light rail instead. Light in this context is used in the sense of "intended for light loads and fast movement", rather than referring to physical weight, since the vehicles often weigh more than those on so-called heavy rail systems. The investment in infrastructure is also usually lighter than would be found for a heavy rail system.
The American Public Transportation Association (APTA) in its Glossary of Transit Terminology defines light rail as: "An electric railway with a 'light volume' traffic capacity compared to heavy rail. Light rail may use shared or exclusive rights-of-way, high or low platform loading and multi-car trains or single cars." However, some diesel powered transit calls itself light rail, such as the O-Train in Ottawa, Canada and River Line in New Jersey, United States, which use diesel multiple unit cars. In traditional transit terminology, these would perhaps be considered commuter rail lines, or branch lines, or interurbans. (If those lines had been electric, they would clearly be interurbans.)
Light rail is similar to the British English term light railway, long used to distinguish railway operations carried out under a less rigorous set of regulation using lighter equipment at lower speeds from mainline railways. Light rail is a generic international English phrase for these types of rail systems which means more or less the same thing throughout the Anglosphere.
The use of the generic term light rail avoids some serious incompatibilities in British and American English. The word tram, for instance, is generally understood in the U.K. and many former British colonies as a synonym for streetcar, but in North America it can instead refer to an aerial tramway. (The usual British term for an aerial tramway is cable car, which in the U.S. usually refers to a ground-level car pulled along by subterranean cables.) The word trolley is often used as a synonym for streetcar in the United States, but is usually taken to mean a cart, particularly a shopping cart, in the U.K. and elsewhere. Many North American transportation planners reserve streetcar for traditional vehicles that operate exclusively in mixed traffic on city streets, while they use light rail to refer to more modern vehicles operating mostly in exclusive rights of way, since they may operate both side-by-side targeted at different passenger groups.
The difference between British English and American English terminology arose in the late nineteenth century when Americans adopted German American rather than British terminology for their electric street railways. German immigrants (who were more numerous than British immigrants in the industrialized Northeast) translated the German term Straßenbahn (literally "street railway") into streetcar rather than tram. A further difference arose because, while Britain abandoned all of its trams except Blackpool after World War II, seven major North American cities (Toronto, Boston, Philadelphia, San Francisco, Pittsburgh, Newark, and New Orleans) continued to operate large streetcar systems. When these cities upgraded to new technology, they called it light rail to differentiate it from their existing streetcars since some continued to operate both the old and new systems. Since the 1980s, Portland, Oregon has built all three types of system: a high capacity light rail system in dedicated lanes and rights-of-way, a low capacity streetcar system integrated with street traffic, and an aerial tram system.
The opposite phrase heavy rail, used for higher capacity, higher speed systems also avoids some incompatibilities in terminology between British and American English, as for instance in comparing the London Underground to the New York Subway. Conventional rail technologies including high-speed, freight, commuter/regional, and metro/subway/elevated urban transit systems are considered to be "heavy rail". People movers and personal rapid transit are even "lighter," at least in terms of capacity. Monorail is a separate technology which has been more successful in specialized services than in a commuter transit role.
The most difficult distinction to draw is that between light rail and streetcar or tram systems. There is a significant amount of overlap between the technologies, many of the same vehicles can be used for either, and it is common to classify streetcars/trams as a subtype of light rail rather than as a distinct type of transportation. The two general versions are:
Many light rail systems - even fairly old ones - have a combination of the two, with both on road and off-road sections. In some countries (esp. in Europe), only the latter is described as light rail. In those places, trams running on mixed right of way are not regarded as light rail, but considered distinctly as streetcars or trams. However, the requirement for saying that a rail line is "separated" can be quite minimal - sometimes just with concrete "buttons" to discourage automobile drivers from getting onto the tracks.
There is a significant difference in cost between these different classes of light rail transit. The traditional style is often less expensive by a factor of two or more. Despite the increased cost, the more modern variation (which can be considered as "heavier" than old streetcar systems, even though it is called "light rail") is the dominant form of urban rail development in the United States.
Some systems, such as the AirTrain JFK in New York City and DLR in London and Kelana Jaya Line in Kuala Lumpur, Malaysia have dispensed with the need for an operator. The Vancouver SkyTrain was an early adopter of driverless vehicles, while the Toronto Scarborough rapid transit operates the same trains as Vancouver, but uses drivers.
Ultra light rail schemes are designed to offer high cost effectiveness and also easy deployment by using modern techniques and materials to dramatically reduce the weight of the vehicles. Ultra light vehicles cannot as a result co-exist with heavy rail or even most light rail systems as the light construction, comparable to that of a car or bus, is insufficiently strong to take an impact with a conventional train. It is however perfectly adequate in the event of collisions with road vehicles or other ultra light rail vehicles. Keeping the weight down allows for energy efficiency comparable with or better than a bus and regular stopping points using nothing more than a cheap gasoline/petrol engine and flywheel. In addition the low weight reduces the cost of track and civil engineering and thus the otherwise high initial construction costs.
See main article: History of Trams.
See also: Interurban.
Many original tram and streetcar systems in the United Kingdom, United States, and elsewhere, were decommissioned in the 1950s and onward as the popularity of the automobile increased. Britain abandoned its last tram system, except for Blackpool, by 1962. Although some traditional trolley or tram systems still exist to this day, the term "light rail" has come to mean a different type of rail system. Modern light rail technology has primarily German origins, since an attempt by Boeing Vertol to introduce a new American light rail vehicle was a technical failure. After World War II, the Germans retained their streetcar networks and evolved them into model light rail systems (stadtbahnen). Except for Hamburg, all large and most medium-sized German cities maintain light rail networks.
The basic concepts of light rail were put forward by H. Dean Quinby in 1962 in an article in Traffic Quarterly called "Major Urban Corridor Facilities: A New Concept". Quinby distinguished this new concept in rail transportation from historic streetcar/tram systems as:
The term light rail transit (LRT) was introduced in North America in 1972 to describe this new concept of rail transportation.
The first of the new light rail systems in North America began operation in 1978 when the Canadian city of Edmonton, Alberta adopted the German Siemens-Duewag U2 system, followed three years later by Calgary, Alberta and San Diego, California. The concept proved popular, and although Canada has few cities big enough for light rail, there are now at least 30 light rail systems the United States.
Britain began replacing its run-down local railways with light rail in the 1980s, starting with Tyneside and followed by the Docklands Light Railway (DLR) in London. The historic term light railway was used because it dated from the British Light Railways Act 1896, although the technology used in the DLR system was at the high end of what Americans considered to be light rail. The trend to light rail in the United Kingdom was firmly established with the success of the Manchester Metrolink system in 1992.
Historically, the rail gauge has had considerable variations, with narrow gauge common in many early systems. However, most light rail systems are now standard gauge. Older standard gauge vehicles could not negotiate sharp turns as easily as narrow gauge ones, but modern light rail systems achieve tighter turning radii by using articulated cars. An important advantage of standard gauge is that standard railway maintenance equipment can be used on it, rather than custom-built machinery. Using standard gauge also allows light rail vehicles to be moved around conveniently using the same tracks as freight railways. Another factor favoring standard gauge is that accessibility laws are making low-floor trams mandatory, and there is generally insufficient space for wheelchairs to move between the wheels in a narrow gauge layout.
With its mix of right-of-way types and train control technologies, LRT offers the widest range of latitude of any rail system in the design, engineering, and operating practices. The challenge in designing light rail systems is to realize the potential of LRT to provide fast, comfortable service while avoiding the tendency to over-design that results in excessive capital costs beyond what is necessary to meet the public's needs.
LRVs are distinguished from rapid rail transit (RRT) vehicles by their capability for operation in mixed traffic, generally resulting in a narrower car body and articulation in order to operate in a traffic street environment. With their large size, large turning radius, and often an electrified third rail, RRT vehicles cannot operate in the street. Since LRT systems can operate using existing streets, they often can avoid the cost of expensive subway and elevated segments that would be required with RRT.
Conversely, LRVs generally outperform streetcars in terms of capacity and top end speed, and almost all modern LRVs are capable of multiple-unit operation. Particularly on exclusive rights-of-way, LRVs can provide much higher speeds and passenger volumes than a streetcar. Thus a single-unit streetcar capable of only 70km/h operating on an shared right of way is not generally considered “light rail”. The latest generation of LRVs is considerably larger and faster, typically of length of 29m (95feet) with maximum speed around 105km/h.
A variation many cities consider is to use historic or replica cars on their streetcar systems instead of modern LRVs. A heritage streetcar may not have the capacity and speed of an LRV, but it will add to the ambiance and historic character of its location.
|Type||Rapid Transit||Light Rail||Streetcar|
|Manufacturer||Rohr||Siemens||St. Louis Car|
|Width||3.2m (10.5feet)||2.7m (08.9feet)||2.5m (08.2feet)|
|Length||22.9m (75.1feet)||27.7m (90.9feet) (articulated)||14.2m (46.6feet)|
|Capacity||150 max||220 max||65 max|
A derivative of LRT is light rail rapid transit (LRRT), also referred to as Light Metro. Such railways are characterized by exclusive rights of way, advanced train control systems, short headway capability, and floor level boarding. These systems approach the passenger capacity of full metro systems, but can be cheaper to construct by using the ability of LRVs to turn tighter curves and climb steeper grades than standard RRT vehicles.
An important factor crucial to LRT is the train operator. Unlike rail rapid transit, traveling unattended with automatic train operation (ATO), the operator is a key element in a safe, high-quality LRT operation. The reason that the operator is so important is because the train tracks often run on roads with cars. If trains were automated on roads, a person wouldn't be there to stop the train if a car pulled in front of it. Light rail trains are actually very heavy to prevent damage from impacts with cars. Thus, a train with ATO is not “light rail”. The philosophy of light rail is that a qualified person should be on each train to deal with emergencies, and while that person is there, he or she might as well operate the train.
The latest generation of LRVs has the advantage of partial or fully low-floor design, with the floor of the vehicles only 300 to 360 mm (12-14 inches) above top of rail, a capability not found in either rapid rail transit vehicles or streetcars. This allows them to load passengers, including ones in wheelchairs, directly from low-rise platforms that are not much more than raised sidewalks. This satisfies requirements to provide access to disabled passengers without using expensive wheelchair lifts, while at the same time making boarding faster and easier for other passengers as well.
Overhead lines supply electricity to the vast majority of light rail systems. This avoids the danger of passengers stepping on an electrified third rail. The Docklands Light Railway uses a standard third rail for its electrical power. Trams in Bordeaux, France use a special third-rail configuration where the power is only switched on beneath the trams, making it safe on city streets. Several systems in Europe, as well as a few recently-opened systems in North America use diesel-powered trains.
All transit service involves a tradeoff between speed and frequency of stops. Services that stop frequently have lower overall speed, and are therefore less attractive for longer trips. Heavy rail, light rail, monorail, and Bus Rapid Transit are all forms of rapid transit — which generally signifies high speed and widely-spaced stops. Trams are a form of local transit, making more frequent stops.
See main article: Tram and light-rail transit systems.
Around the world there are many tram systems; some date back from the early 20th century but countless number of the old systems were closed down with the exception of many Eastern Europe countries in the mid-20th century. Even though many of the systems have closed down over the years there are still tram systems that have been operating much as they did when they were first built over a century ago. Some cities (such as Los Angeles and Jersey City) that have once closed down their tram networks are now in the stages of reconstructing, or have rebuilt, some of their tramways.Most of light rail services are currently committed to articulated vehicles like modern LRVs, i.e. trams, with exception of large underground metrosystems.
One line of light rail has more than 8 times the capacity of one lane of freeway during peak times. Roads have ultimate capacity limits which can be determined by traffic engineering. They usually experience a chaotic breakdown in flow and a dramatic drop in speed (colloquially known as a traffic jam) if they exceed about 2,000 vehicles per hour per lane (each car roughly two seconds behind another). Since most people who drive to work or on business trips do so alone, studies show that the average car occupancy on many roads carrying commuters is only about 1.2 people per car during the high-demand rush hour periods of the day. . This combination of factors limits roads carrying only automobile commuters to a maximum of about 2,400 passengers per hour per lane. The problem can be mitigated by using high-occupancy vehicle (HOV) lanes and introducing ride-sharing programs, but in most cases the solution adopted has been to add more lanes to the roads. Simple arithmetic shows that in order to carry 20,000 automobile commuters per hour per direction, a freeway must be at least 18 lanes wide.
By contrast, light rail vehicles can travel in multi-car trains carrying up to 20,000 passengers per hour in much narrower rights-of-way, not much more than two car lanes wide for a double track system. They can often be run through existing city streets and parks, or placed in the medians of roads. If run in streets, trains are usually limited by city block lengths to about four 180-passenger vehicles (720 passengers). Operating on 2 minute headways using traffic signal progression, a well-designed two-track system can handle up to 30 trains per hour per track, achieving peak rates of over 20,000 passengers per hour in each direction. More advanced systems with separate rights-of-way using moving block signalling can exceed 25,000 passengers per hour per track.
Most North American light rail systems are limited by demand rather than capacity and seldom reach 10,000 passengers per hour per track, and measuring the passengers per actual mile of trackage vs passengers carried per urban freeway lanes, the urban freeway lane carries more traffic for a far smaller government subsidy, but systems elsewhere in the world often have much higher passenger volumes. The Manila Light Rail Transit System is one of the highest capacity ones, having being upgraded in a series of expansions to handle 40,000 passengers per hour per direction, and currently carrying up to 400,000 passengers per day on its Line #1. It achieves this volume by running 4-car trains of up to 1350 passengers at a frequency of up to 30 trains per hour.
The cost of light rail construction varies widely, largely depending on the amount of tunneling and elevated structures required. A survey of North American light rail projects shows that costs of most LRT systems range from $15 million per mile to over $100 million per mile. Seattle's new light rail system is by far the most expensive in the U.S. at $179 million per mile, since it includes extensive tunneling in poor soil conditions, elevated sections, and stations as deep as 180 feet below ground level. These result in costs more typical of subways or rapid transit systems than light rail. At the other end of the scale, four systems (Baltimore MD, Camden NJ, Sacramento CA, and Salt Lake City UT) incurred costs of less than $20 million per mile. Over the U.S. as a whole, excluding Seattle, new light rail construction costs average about $35 million per mile. By comparison, a freeway lane expansion typically costs $20 million per lane mile for two directions.  Since a light rail line can carry 20,000 people per hour as compared with 2,400 people per hour for a freeway lane during peak times, light rail delivers 4 times the congestion-reduction potential per dollar as incremental freeway lanes.
Combining highway expansion with LRT construction can save costs by doing both highway improvements and rail construction at the same time. As an example, Denver's T-REX (Transportation Expansion) project rebuilt interstate highways 25 and 225 and added a light-rail expansion for a total cost of $1.67 billion over five years. The cost of 17 miles of highway improvements and 19 miles of double-track light rail worked out to $19.3 million per highway lane-mile and $27.6 million per LRT track-mile. The project came in under budget and 22 months ahead of schedule.
LRT cost efficiency improves dramatically as ridership increases, as can be seen from the numbers above: the same rail line, with similar capital and operating costs, is far more efficient if it is carrying 20,000 people per hour than if it is carrying 2400. The Calgary, Alberta C-Train used many common light rail techniques to keep costs low, including minimizing underground and elevated trackage, sharing transit malls with buses, leasing rights-of-way from freight railroads, and combining LRT construction with freeway expansion. As a result, Calgary ranks toward the less expensive end of the scale with capital costs of around $24 million per mile.
However, Calgary's LRT ridership is much higher than any comparable U.S. city at over 250,000 rides per weekday and as a result its efficiency of capital is also much higher. Its capital costs were ⅓ that of the San Diego system, a comparably sized one in the U.S., while its ridership is approximately twice as high. Thus, Calgary's capital cost per weekday rider is less than one quarter that of San Diego. Its operating costs are also lower. A typical C-Train vehicle costs only $163 per hour to operate, and since it averages 600 passengers per operating hour, Calgary Transit estimates that its LRT operating costs are only 27 cents per ride, versus $1.50 per ride on its buses.
Around Karlsruhe, Kassel and Saarbrücken in Germany, dual-voltage light rail trains partly use mainline railroad tracks, sharing these tracks with heavy-rail trains. In the Netherlands, this concept was first applied on the RijnGouweLijn. This allows commuters to ride directly into the city centre, rather than taking a mainline train only as far as a central station and then having change to a tram. In France similar tram-trains are planned for Paris, Mulhouse and Strasbourg; further projects exist.
Some of the issues involved in such schemes are:
There is a history of what would now be considered light-rail vehicles operating on heavy-rail rapid transit tracks in the U.S., especially in the case of interurban streetcars. Notable examples are Lehigh Valley Transit trains running on the Philadelphia and Western Railroad high-speed third rail line (now the Norristown High Speed Line). Such arrangements are almost impossible now, due to the Federal Railroad Administration refusing (for crash safety reasons) to allow non-FRA compliant railcars (i.e. subway and light rail vehicles) to run on the same tracks at the same times as compliant railcars, which includes locomotives and standard railroad passenger and freight equipment. A notable exception is the New Jersey Transit River Line from Camden to Trenton, which has received an exemption on the provision that light rail operations occur only during daytime hours and Conrail freight service only at night, with several hours separating one operation from the other.
See also: Karlsruhe model.
See main article: Ground-level power supply. In the French city of Bordeaux, Citadis trams are powered by a third rail in the city center, where the tracks are not always segregated from pedestrians and cars. The third rail (actually two closely spaced rails) is placed in the middle of the track, and divided into eight-metre sections, each of which is only powered while it is completely covered by a tram. This minimises the risk of a person or animal coming into contact with a live rail. In outer areas, the trams switch to conventional overhead wires.
In practice the Bordeaux power system cost about three times as much as a conventional overhead wire system and took 24 months to achieve acceptable levels of reliability, requiring replacement of all the main cables and power supplies. Operating and maintenance costs of the innovative power system still remain high. However, despite numerous service outages, the system was a success with the public, gaining up to 190,000 passengers per day.