Light-Rail基础简明介绍

LightRail

Lightrailorlightrailtransit(LRT)isaparticularclassofurbanandsuburbanpassengerrailwaythatusesequipmentandinfrastructurethatisgenerallylessmassivethanthatusedforrapidtransitsystems,withmodernlightrailvehiclesusuallyrunningalongthesystem.

Lightrailisthesuccessortermtostreetcar,trolleyandtraminmanylocales,althoughthetermismostconsistentlyappliedtomoderntramortrolleyoperationsemployingfeaturesmoregenerallyassociatedwithmetroorsubwayoperations,includingexclusiverights-of-way,multipleunittrainconfigurationandsignalcontrolofoperations.

ThetermlightrailisderivedfromtheBritishEnglishtermlightrailwaylongusedtodistinguishtramoperationsfromsteamrailwaylines,andalsofromitsusuallylighterinfrastructure.

Lightrailsystemsarealmostuniversallyoperatedbyelectricitydeliveredthroughoverheadlines,thoughseveralsystemsarepoweredthroughdifferentmeans,suchasthe

JFKAirtrain,whichusesastandardthirdrailforitselectricalpower,andtramsinBordeauxwhichuseaspecialthird-railconfigurationinwhichtherailisonlypoweredwhileatramisontopofit.AfewunusualsystemsliketheRiverLineinNewJerseyandthe0-TraininOttawausediesel-poweredtrains,thoughthisissometimesintendedasaninterimmeasureuntilthefundstoinstallelectricpowerbecomeavailable.

Definition

Mostrailtechnologies,includinghigh-speed,freight,commuter/regional,andmetro/subwayareconsideredtobe"heavyrail"incomparison.Afewsystemssuchaspeoplemoversandpersonalrapidtransitcouldbeconsideredaseven"lighter",atleastintermsofhowmanypassengersaremovedpervehicleandthespeedatwhichtheytravel.Monorailsarealsoconsideredtobeaseparatetechnology.Lightrailsystemscanhandlesteeperinclinesthanheavyrail,andcurvessharpenoughtofitwithinstreetintersections.Theyaregenerallybuiltinurbanareas,providingfrequentservicewithsmall,lighttrainsorsinglecars.

Themostdifficultdistinctiontodrawisthatbetweenlightrailandstreetcarortramsystems.Thereisasignificantamountofoverlapbetweenthetechnologies,anditisusualtoclassifystreetcars/tramsasasubtypeoflightrailinsteadofasadistincttypeoftransportation.Thetwocommonversionsare:

1.Thetraditionaltype,wherethetracksandtrainsrunalongthestreetsandsharespacewithroadtraffic.Stopstendtobeveryfrequent,butlittleeffortismadetosetupspecialstations.Becausespaceisshared,thetracksarenotusuallyvisible.

2.Amoremodernvariation,wherethetrainstendtorunalongtheirownright-of-wayandareof-tenseparatedfromroadtraffic.Stopsareusuallylessfrequent,andthevehiclesareoftengotonfromaplatform.Tracksarehighlyvisible,andinsomecasessignificanteffortisusedtokeeptrafficawaythroughtheuseofspecialsignalingandevengradecrossingswithgatearms.Atthehighestdegreeofseparation,itcanbedifficulttodrawthelinebetweenlightrailandmetros,asinthecaseofLondon'sDocklandsLightRailway,whichwouldlikelynotbeconsidered"light"comparedwithLondonUnderground.

Manylightrailsystemshaveacombinationofthetwo,withbothonroadandoffroadsections.Insomecountries,onlythelatterisdescribedaslightrail.Inthoseplaces,tramsrunningonmixedrightofwayarenotregardedaslightrail,butconsidereddistinctlyasstreetcarsortrams.

Lightrailisusuallypoweredbyelectricity,generallybymeansofoverheadwires,butsometimesbyaliverail,alsocalledthirdrail(ahighvoltagebaralongsidethetrack),requiringsafetymeasuresandwarningstothepublicnottotouchit.Insomecases,especiallywheninitialfundsarelimited,diesel-poweredversionshavebeenused,butitis

notapreferredoption.Somesystems,suchastheJFKAirtraininNewYorkCity,are

automaticwithoutadriver;however,suchsystemsarenotwhatisusuallythoughtofaslightrail.Automaticoperationismorecommoninsmallerpeoplemoversystemsthaninlightrailsystems,wherethepossibilityofgradecrossingsandstreetrunningmakedriverlessoperationofthelatterinappropriate.

Advantagesoflightrail

Lightrailsystemsareusuallycheapertobuildthanheavyrail,sincetheinfrastructuredoesnotneedtobeconsiderable,andtunnelsareusuallynotrequiredasmostmetrosystems.Inaddition,theabilitytohandlesharpcurvesandsteepgradientscanreducetheamountofworkrequired.

Traditionalstreetcarsystemsandalsonewerlightrailsystemsareusedinmanycitiesaroundtheworldbecausetheygenerallycancarryalargernumberofpeoplethananybus-basedpublictransportsystem.Theyarealsocleaner,quieter,morecomfortable,andinmanycasesfasterthanbuses.Inanemergency,lightrailtrainsareeasiertoevacuatethanmonorailorelevatedrapidrailtrains.

Manymodernlightrailprojectsre-usepartsofoldrailnetworks,suchasabandonedindustrialraillines.

Disadvantagesoflightrail

Likeallmodesofrailtransport,lightrailtendstobesafestwhenoperatingindedicatedright-of-waywithcompletegradeseparations.Nevertheless,gradeseparationsarenotalwaysfinanciallyorphysicallyfeasible.

InCalifornia,thedevelopmentoflightrailsystemsinLosAngelesandSanJosecausedahighrateofcollisionsbetweenautomobilesandtrolleysduringthe1990s.Themostcommoncausewasthatmanyseniorcitizenswereunfamiliarwithlightrailtrolleysandoftenmistookthetrolley"T"signallightsforleft-turnsignallights.Theywouldthenmakealeftturn,rightintothepathofatrolley.ThesamehighcrashrateproblemexistedwhentheMETRORailwasfirstsetupinHouston,Texas.

Toreducesuchcollisions,brighterlightsandlouderwarningklaxonshavebeenaddedt