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Typical rolling stock
Type Rapid Transit Light Rail Streetcar
Manufacturer Rohr Siemens St. Louis Car
Model BART A-Car S70 PCC
Width 3.2 m (10.5 ft) 2.7 m (8.7 ft) 2.5 m (8.3 ft)
Length 22.9 m (75 ft) 27.7 m (91 ft) 14.2 m (47 ft)
Capacity 150 max 220 max 65 max
Top Speed 125 km/h (80 mph) 106 km/h (66 mph) 70 km/h (45 mph)
Light metro
For more details on this topic, see Medium capacity system.
A derivative of LRT is light rail rapid transit (LRRT), also referred to as
Light Metro. Such railways are characterized by exclusive rights of way,
advanced train control systems, short headway capability, and floor level
boarding. These systems approach the passenger capacity of full metro systems,
but can be cheaper to construct by using the ability of LRVs to turn tighter
curves and climb steeper grades than standard RRT vehicles.
Train operation
For more details on this topic, see Automatic train operation.
An important factor crucial to LRT is the train operator. Unlike rail rapid
transit, traveling unattended with automatic train operation (ATO), the operator
is a key element in a safe, high-quality LRT operation[citation needed]. Thus, a
train with ATO is not “light rail”. The philosophy of light rail is that a
qualified person should be on each train to deal with emergencies[citation
needed], and while that person is there, he or she might as well operate the
train.
Floor height
For more details on this topic, see Low floor.
The latest generation of LRVs has the advantage of partial or fully low-floor
design, with the floor of the vehicles only 300 to 360 mm (12-14 inches) above
top of rail, a capability not found in either rapid rail transit vehicles or
streetcars. This allows them to load passengers, including ones in wheelchairs,
directly from low-rise platforms that are not much more than raised sidewalks.
This satisfies requirements to provide access to disabled passengers without
using expensive wheelchair lifts, while at the same time making boarding faster
and easier for other passengers as well.
Power sources
Overhead lines supply electricity to the vast majority of light rail systems.
This avoids the danger of passengers stepping on an electrified third rail. The
Docklands Light Railway uses a standard third rail for its electrical power.
Trams in Bordeaux, France use a special third-rail configuration where the power
is only switched on beneath the trams, making it safe on city streets. Several
systems in Europe, as well as a few recently-opened systems in North America use
diesel-powered trains.
Pros and cons of Light Rail
Main article: Tram system#Pros and cons of tram systems
All transit service involves a tradeoff between speed and frequency of stops.
Services that stop frequently have lower overall speed, and are therefore less
attractive for longer trips. Metros, light rail, monorail, and Bus Rapid Transit
are all forms of rapid transit — which generally signifies high speed and
widely-spaced stops. Trams are a form of local transit, making frequent stops.
Light rail around the world
Main article: Tram system#Regional variations
Capacity of light rail versus roads
Roads have capacity limits which can be determined by traffic engineers. Due to
traffic congestion they experience a chaotic breakdown in flow and a dramatic
drop in speed if they exceed about 2,000 vehicles per hour per lane. Since
automobiles in many places average only 1.2 passengers during rush hour, this
limits roads to about 2,400 passengers per hour per lane. This can be mitigated
somewhat by using high-occupancy vehicle (HOV) lanes.
Light rail vehicles can travel in trains carrying much higher passenger volumes.
If run in streets, light rail systems are limited by city block lengths to about
four 180-passenger vehicles (720 passengers). Operating on 2 minute headways
using traffic signal progression, a well-designed system can handle more than 30
trains per hour, achieving peak rates of over 20,000 passengers per hour per
track. More advanced systems with separate rights-of-way using moving block
signalling can exceed 25,000 passengers per hour per track.
Most North American systems are limited by demand rather than capacity and
seldom reach 10,000 passengers per hour per track, but European light rail
systems often approach their limits. When they do, they can carry as many
passengers as a 16-lane freeway in the space of a two lane roadway. If passenger
volumes exceed light rail limits, heavy rail systems can be built to carry many
more people.
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