Light rail



         


Light rail is a particular class of railway that includes trolleys and trams as well as modern multi-car trains that operate at street level. The exact meaning is difficult or impossible to define, as it has varied over time and between different regions. The name derives from the fact that the vehicles are lighter and don't require rail tracks to be as massive. Modern light rail systems are descended from the rail lines that existed in the 19th and early 20th centuries and the technologies developed for them.

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Attempting to define "light rail"

Most rail technologies, including high-speed, freight, commuter/regional, and metro/subway are considered to be "heavy rail" in comparison. A few systems such as people movers and personal rapid transit could be considered as even "lighter", at least in terms of how many passengers are moved per vehicle and the speed at which they travel. Monorails are also considered to be a separate technology. Light-rail systems can handle steeper inclines than heavy rail, and curves sharp enough to fit within street intersections (though this is hardly true for all light-rail lines). They are typically built in urban areas, providing frequent service with small, light trains or single cars.

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, and it is common classify streetcars/trams as a subtype of light rail rather than 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 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 and even grade crossings with gate arms.

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, 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.

They are generally powered by electricity, usually by means of overhead wires, but sometimes by a live rail, also called third rail (a high voltage bar alongside the track), requiring safety measures and warnings to the public not to touch it. In some cases, particularly when initial funds are limited, diesel-powered versions have been used, but it is not a preferred option. Some systems are automatic, dispensing with the need for a driver, although automatic operation is more common in smaller people mover systems.

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History

From the mid-19th century onwards, horse-drawn trams were used in many cities around the world. In around the 1880s electrically driven street railways became technically feasible. They became popular because roads were then poorly surfaced, and before the invention of the internal combustion engine and the advent of motor-buses, they were the only practical means of public transport around cities.

The light-rail systems constructed in the 19th and early 20th centuries typically only ran in single-car setups. Some rail lines experimented with multiple unit configurations, where streetcars were joined together to make short trains, but this didn't become common until later. When lines were build over longer distances (typically with a single track) before good roads were common, they were generally called interurbans in North America, or radial railways in Ontario.

In North America, many of these original light-rail systems were decommissioned in the 1950s and onward as the popularity of the automobile increased. Although some traditional trolley or tram systems still exists to this day, the term "light rail" has come to mean a different type of rail system. Beginning in the 1980s, some cities began reintroducing light-rail systems that are more like subway or metro train systems that operate at street level. These light-rail systems include modern, multi-car trains that can only be accessed at stations that are spaced anywhere from a couple blocks to a mile or more apart. Some of these systems operate within roadways alongside automobile traffic, and others operate on their own separate right-of-way.

As with other rail systems, the rail gauge has had considerable variations, but today standard gauge is dominant. Narrow gauge was common in many earlier systems, although as systems merged or died out, old lines were often upgraded, removed, or replaced. Some systems still use other track gauges, however.

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Advantages of light rail

Light-rail systems are generally cheaper to build than heavy rail, since the infrastructure does not need to be as substantial, and tunnels are generally not required as is the case with most metro systems. Moreover, the ability to handle sharp curves and steep gradients can reduce the amount of work required.

Traditional streetcar systems as well as newer light-rail systems are used in many cities around the world because they typically can carry a larger number of people than any bus-based public transport system. They are also cleaner, quieter, more comfortable, and in many cases faster than buses.

Many modern light-rail projects re-use parts of old rail networks, such as abandoned industrial rail lines.

A good example of both points above is the Docklands Light Railway (DLR) in London, which uses a sharp, steep, curve to enable it to transfer from running alongside an existing railway line to a disused railway line which crossed underneath the first line. A direct connection between these lines would not be practical for conventional rail (note that because the DLR has a completely grade separated right of way, it can also be regarded as a metro).

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Unusual variations

Luas is a project at an advanced stage of construction in Dublin, Ireland. It is a light-rail/tram system which will run on dedicated on-road rail tracks.

Around Karlsruhe and Saarbrücken, Germany, light-rail vehicles partly use heavy-rail tracks, sharing these tracks with heavy-rail trains. In the Netherlands this was first applied on the RijnGouweLijn.

Some of the issues involved are:

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See also

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