Light rail


 * 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. The term is used to refer to modern streetcar/tram 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.

Light rail, unlike rapid transit, is not fully grade-separated from other forms of traffic and thus is a step below a true rapid transit system.

Definition of light rail
The term light rail was devised in 1972 by the U.S. Urban Mass Transit Association (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 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 Authority (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 be considered commuter rail lines.

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 common British word for streetcar, tram, is commonly used in the United States to mean an aerial tramway, while the usual British term for an aerial tramway, cable car, usually means a ground-level cable car in the U.S. The word trolley which is often used as a synonym for streetcar in the United States, is usually taken to mean a cart, particularly a shopping cart, in Britain. Most former British colonies use the British term tram, but in Canada the American term streetcar is preferred. 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 WWII, 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. Portland, Oregon built all three types of light rail/streetcar/tram system: a high capacity light rail system, a low capacity streetcar system, 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 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.

Categories of light rail
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:
 * 1) The traditional type, where the tracks and trains run along the streets and share space with road traffic. Stops tend to be very frequent, but little effort is made to set up special stations. Because space is shared, the tracks are usually visually unobtrusive.
 * 2) A more modern variation, where the trains tend to run along their own right-of-way and are often separated from road traffic. Stops are generally less frequent, and the vehicles are often boarded from a platform. Tracks are highly visible, and in some cases significant effort is expended to keep traffic away through the use of special signaling, level crossings with gate arms or even a complete separation with non-level crossings. At the highest degree of separation, it can be difficult to draw the line between light rail and metros, as in the case of Wuppertal's Schwebebahn hanging rail system or London's Docklands Light Railway, which would likely not be considered "light" were it not for the contrast between it and the London Underground. Increasingly, light rail is being used to describe any rapid transit system with a fairly lower frequency compared to heavier mass rapid systems such as the London Underground or the Mass Rapid Transit in Singapore.

Many light rail systems &mdash; even fairly old ones &mdash; 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 &mdash; 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 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.

History
Many original Tram and Streetcar systems were decommissioned in the 1950s and onward as the popularity of the automobile increased. Britain abandoned its last Tram system except 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 renaissance of light rail in North America began 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. Britain began replacing its run-down local railways with light rail in the 1980s, starting with Tyneside and followed by the Docklands Light Railway in London. 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. 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 delivered and relocated conveniently using freight railways and locomotives. Another factor favoring standard gauge is that low-floor vehicles are becoming popular, and there is generally insufficient space for wheelchairs to move between the wheels in a narrow gauge layout.

Comparison to other rail transit modes
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.

Rapid rail transit
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. Due to 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.

Streetcars or trams
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 70 km/h (45 mph) 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 29 m with maximum speed around 105 km/h.

Heritage streetcar
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.

Light metro
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.

Train operation
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. 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.

Floor height
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.

Power sources
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.

Pros and cons of light rail
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. Metros, 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.

Tram and light-rail transit systems around the world
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 that have once closed down their tram networks are now in the stages of reconstructing their tramways.

Capacity of light rail versus roads
Roads have capacity limits which can be determined by traffic engineers. Due to traffic congestion they experience a chaotic breakdown in flow and a dramatic drop in speed if they exceed about 2,000 vehicles per hour per lane (each car roughly 2 seconds behind another). Since automobiles in many places average only 1.2 passengers during rush hour, this limits roads to about 2,400 passengers per hour per lane. This can be mitigated somewhat by using high-occupancy vehicle (HOV) lanes.

Light rail vehicles can travel in trains carrying much higher passenger volumes. If run in streets, light rail systems are 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 system can handle more than 30 trains per hour, achieving peak rates of over 20,000 passengers per hour per track. More advanced systems with separate rights-of-way using moving block signalling can exceed 25,000 passengers per hour per track.

Most North American systems are limited by demand rather than capacity and seldom reach 10,000 passengers per hour per track, but European light rail systems often approach their limits. When they do, they can carry as many passengers as a 16-lane freeway in the space of a two lane roadway. If passenger volumes exceed light rail limits, heavy rail systems can be built to carry many more people.

Costs of light rail construction and operation
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.

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. 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 1/6 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.

Trams operating on mainline railways
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:
 * compatibility of the safety systems
 * power supply of the track in relation to the power used by the vehicles (frequently different voltages, rarely third rail vs overhead wires)
 * width of the vehicles in relation to the position of the platforms
 * height of the platforms

There is 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.

Third-rail power for trams
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.

This third rail technology is being investigated for use on the Gold Coast of Australia for the Gold Coast Light Rail. See the present draft report here.