Light rail1 is a form of urban rail transportation that has evolved from trams (also referred to as streetcars or trolleys) and has characteristics intermediate between those of trams and rapid transit. These characteristics make it well suited for situations in which it is desirable to have higher speeds and greater capacity than trams but lower construction costs, greater routing flexibility and increased user convenience as compared with rapid transit.
A main difference is that, whereas trams mostly operate on tracks embedded in streets together with automobiles and other road traffic, light rail tracks are usually mostly located on exclusive rights of way, which are often strips of land adjacent to streets or in the medians of streets. They can also be located elsewhere at surface level or on elevated structures or in tunnels as is the case with rapid transit. Moreover, they can additionally be built into streets or transit malls for parts of their routes, and in some cases they share sections of street track with existing tram lines and even operate over conventional heavy rail track.
This predominantly off-street operation allows light rail vehicles to operate at substantially faster speeds than trams. Adding to the higher speed is the frequent use of signal priority at intersections, both where the light rail vehicles operate in streets and where they operate on exclusive rights of way. Speed typically is also enhanced by a greater distance between stops than for trams.
This great flexibility with regard to routing, including the ability to operate in or adjacent to streets as well as in transit malls, gives light rail a much lower construction cost than rapid transit. It also adds to the convenience for users because it allows them board and alight vehicles without having to descend into tunnels or ascend up to elevated structures.
The construction of new light rail systems and the expansion and upgrading of existing light rail and tram systems has been undergoing a boom worldwide during the past several decades. This is because of ever-increasing traffic congestion and growing awareness about the harmful effects of air pollution. It is also because city planners and environmental experts have increasingly recognized that this form of urban transportation can, with good planning, be far superior to ever more cars, ever wider freeways, and ever more parking lots for increasing mobility, minimizing energy consumption, reducing air pollution, and generally improving the quality of urban life .
Possibly the most outstanding of the many examples of this tram renaissance that could be cited is France. That country scrapped most of its numerous tram systems beginning in the 1930s, replacing them with buses, so that all that eventually remained were just three truncated lines that would have been difficult to replace with buses. Typical reasons given for this swift dismantling were that trams were "obsolete," that they were obstacles to automobile traffic, and that buses allow a lower cost and more flexible operation.
However, as a result of rapidly increasing traffic congestion and air pollution and of growing concern about climate change, this situation underwent a dramatical reversal beginning in the 1980s. In 1985 Nantes, a city of some 320,000 in western France, became the first in Europe to restore trams where they had previously been scrapped. The resounding success of this new, second-generation surface rail system – and then of a succession of other new systems – has so far resulted in more than 30 French cities of all sizes constructing new tram lines, often in conjunction with creating automobile-free tram malls in central areas, restoring historic building facades, adding street furniture, and making other improvements along the new light rail routes. Still more new systems are being planned and many of the existing systems are being expanded. This pattern is being repeated in many other countries, both in Europe and elsewhere.
This success has been manifested in various ways. Ridership has generally been much greater than for the bus routes that the new light rail lines replaced, and often substantially greater than projections. Local air pollution and traffic congestion have decreased as a result of many trips being taken by light rail instead of by private automobile. And the introduction of light rail has often revitalized nearby neighborhoods and led to much new construction.
Meanwhile, light rail technology has continued to advance in numerous ways, resulting in enhanced passenger convenience and comfort, higher speeds, reduced operating costs and greater safety. For example, fully low-floor vehicles have been developed and are now becoming commonplace, thereby making entry and exit easier, faster and safer. This is particularly important for persons with limited mobility as well as for passengers with wheelchairs, baby carriages, bicycles, etc.
Advances in electronic hardware and software have allowed improved real time information for system managers and passengers as well as automated obstacle detection and even semi-automated operation. Also, various technologies have been developed to eliminate the need for overhead wires, which is particularly beneficial for historic areas, including through the use of power collection via circuits built into streets and by using high-performance rechargeable batteries.
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1. The term light rail derives from the much older term light railway, which is a form of rail transportation that, at least originally, used lighter weight vehicles and had lighter weight rails than most conventional railroads.