城市轨道交通专业英语Unit Three.docx

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1、 Text A Light RailLight rail or light rail transit（LET) is a particular class of urban and suburban passenger railway that uses equipment and infrastructure that is generally less massive than that used for rapid transit systems，with modern light rail vehicles usually running along the system. Light

2、 rail is the successor term to streetcar，trolley and tram in many locales，although the term is most consistently applied to modern tram or trolley operations employing features more generally associated with metro or subway operations，including exclusive rights-of-way，multiple unit train configurati

3、on and signal control of operations. The term light rail is derived from the British English term light railway long used to distinguish tram operations from steam railway lines，and also from its usually lighter infrastructure. Light rail systems are almost universally operated by electricity delive

4、red through overhead lines, though several systems are powered through different means，such as the JFK Airtrain，which uses a standard third rail for its electrical power, and trams in Bordeaux which use a special third-rail configuration in which the rail is only powered while a tram is on top of it

5、. A few unusual systems like the River Line in New Jersey and the O-Train in Ottawa use diesel-powered trains，though this is sometimes intended as an interim measure until the funds to install electric power become available.DefinitionMost rail technologies，including high-speed，freight，commuter/ reg

6、ional，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 t

7、o be a separate technology. Light rail systems can handle steeper inclines than heavy rail，and curves sharp enough to fit within street intersections. They are generally built in urban areas，providing frequent service with small，light trains or single cars The most difficult distinction to draw is t

8、hat between light rail and streetcar or tram systems. There is a significant amount of overlap between the technologies，and it is usual to classify street-cars/trams as a subtype of light rail instead of as a distinct type of transportation. The two common versions are： 1.The traditional type，where

9、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 not usually visible. 2. A more modern variation，where the trains tend to run along their own righ

10、t-of-way and are of- ten separated from road traffic. Stops are usually less frequent，and the vehicles are often got on from a platform. Tracks are highly visible，and in some cases significant effort is used to keep traffic away through the use of special signaling and even grade crossings with gate

11、 arms. At the highest degree of separation，it can be difficult to draw the line between light rail and metros，as in the case of Londons Docklands Light Railway，which would likely not be considered“light”compared with London Underground. Many light rail systems have a combination of the two，with both

12、 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. Light rail is usually powered by electricity，generally by means of overhe

13、ad 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，especially when initial funds are limited, diesel-powered versions have been used，but it is not a preferred option.

14、 Some systems，such as the JFK Airtrain in New York City，are automatic without a driver; however, such systems are not what is usually thought of as light rail. Automatic operation is more common in smaller people mover systems than in light rail systems，where the possibility of grade crossings and s

15、treet running make driverless operation of the latter inappropriate.Advantages of light railLight rail systems are usually cheaper to build than heavy rail，since the infrastructure does not need to be considerable，and tunnels are usually not required as most metro systems. In addition，the ability to

16、 handle sharp curves and steep gradients can reduce the amount of work required. Traditional streetcar systems and also newer light rail systems are used in many cities around the world because they generally can carry a larger number of people than any bus-based public transport system. They are al

17、so cleaner, quieter，more comfortable，and in many cases faster than buses. In an emergency，light rail trains are easier to evacuate than monorail or elevated rapid rail trains. Many modern light rail projects re-use parts of old rail networks，such as abandoned industrial rail lines.Disadvantages of l

18、ight railLike all modes of rail transport，light rail tends to be safest when operating in dedicated right-of-way with complete grade separations. Nevertheless，grade separations are not always financially or physically feasible. In California, the development of light rail systems in Los Angeles and

19、San Jose caused a high rate of collisions between automobiles and trolleys during the 1990s. The most common cause was that many senior citizens were unfamiliar with light rail trolleys and often mistook the trolley“T signal lights for left-turn signal lights. They would then make a left turn，right

20、into the path of a trolley. The same high crash rate problem existed when the METRORail was first set up in Houston，Texas. To reduce such collisions，brighter lights and lcuder warning klaxons have been added to many at-grade crossings. However, consequently，many people do not like to live next to li

21、ght rail crossings because the noise makes them impossible to sleep. A more effective means of reducing or preventing automobile-light rail collisions has been the installation of quad crossing gates at gate crossings. These gates block both lanes of a street when the gate closes. These prevent thos

22、e driving automobiles from driving around the gates when they are lowered.Monorail supporters like to point out that light rail trolleys are heavier per pound of cargo carried than heavy rail cars or monorail. cars，because, they must be designed to avoid collisions with automobiles.History of the Li

23、ght RailFrom the mid-19th century, horse-drawn trams(or horse cars ) were used in many cities around the world. In the late 1880s electrically-powered street railways became technically feasible after the invention of a trolley system of collecting current by American inventor Frank J. Sprague who i

24、nstalled the first successful system at Richmond, Virginia. They became popular because roads were then poorly surfaced, and before the invention of the internal combustion engine and the advent of motorbuses, they were the only practical means of public transport around cities. The light rail syste

25、ms built in the 19th and early 20th centuries generally 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 didnt become common until later. When lines were built over longer distances(typ

26、ically with a single track) before good roads were common, they were usually called interurban streetcars 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 increa

27、sed. Though 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. Beginning in the 1980s, some cities began reintroducing light-rail systems that are more like subway or metro systems that operate at street level. Th

28、ese light-rail systems include modern, multi-car trains that can only be reached 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 a lot of variations, but today standard gauge is dominant. Narrow gauge was common in many earlier systems, though as systems merged or died out, old lines were often upgraded, removed, or replaced. Some systems still use other track gauges, however.