Metro Systems and Overhead Lines
Most rapid transit systems are powered by a third rail, but some use pantographs, particularly ones that involve extensive above-ground running. Hybrid metro-tram or 'pre-metro' lines whose routes include tracks on city streets or in other publicly-accessible areas, such as the MBTA Green Line, must of course use overhead wire, since a third rail would normally present too great a risk of electrocution.
One exception to this is the new Bordeaux tram system that uses an underground system called alimentation par le sol, which only applies power to segments of track that are completely covered by the tram. This system is used in the historic centre of Bordeaux where an overhead wire system would cause a visual intrusion.
Overhead pantographs are sometimes used as alternatives to third rails because third rails can ice over in certain winter weather conditions. The MBTA Blue Line or the Wonderland Line uses pantograph power for all of its surface route. The entire Metro systems of Barcelona, Shanghai, Hong Kong, and Seoul use overhead wiring and pantographs. Pantographs were also used on the Nord-Sud Company rapid transit lines in Paris until the other operating company of the time, Compagnie du chemin de fer métropolitain de Paris bought out the company and replaced all overhead wiring with the standard third rail system used on other lines.
Until 2010 the Oslo metro line 1 changed from third rail to overhead line power at Frøen station. Due to the many level crossings, it was deemed difficult to install a third rail on the rest of the older line 1 tracks.
Read more about this topic: Pantograph (rail)
Famous quotes containing the words systems, overhead and/or lines:
“The only people who treasure systems are those whom the whole truth evades, who want to catch it by the tail. A system is just like truth’s tail, but the truth is like a lizard. It will leave the tail in your hand and escape; it knows that it will soon grow another tail.”
—Ivan Sergeevich Turgenev (1818–1883)
“There’s something wonderfully exciting about the quiet sing song of an aeroplane overhead with all the guns in creation lighting out at it, and searchlights feeling their way across the sky like antennae, and the earth shaking snort of the bombs and the whimper of shrapnel pieces when they come down to patter on the roof.”
—John Dos Passos (1896–1970)
“The opera isn’t over till the fat lady sings.”
—Anonymous.
A modern proverb along the lines of “don’t count your chickens before they’re hatched.” This form of words has no precise origin, though both Bartlett’s Familiar Quotations (16th ed., 1992)