articulated trolleybus in
Arnhem]]
A
trolleybus (also known as
electric bus,
trolley bus,
trolley coach,
trackless trolley,
trackless tram or simply
trolley) is a
bus powered by two overhead electric wires, from which the bus draws
electricity using two
trolley poles. Two poles are required in order to accommodate the return current, which can not pass to the ground as in the case of an electric
tram or streetcar since trolleybuses use rubber
tires rather than steel wheels on rail.
A
trolleybus is called a "trackless tram (無軌電車)" in China.
Background
The trolleybus's development dates to the early
1900s, when they seemed to be a natural compromise between the electric streetcar and the petroleum-powered bus. Trolleybus systems could avoid obstacles in the street which a streetcar could not, and did not require as much capital investment as a streetcar line.
Some cities, led by the
Brooklyn-Manhattan Transit Corporation (BMT—New York), subscribed to the
all-four concept of using buses, trolleybuses,
trams (in U.S. called streetcars,
trolleys or
light rail) and
rapid transit subway and/or elevated lines (
metros) as appropriate for routes ranging from lightly-used to heaviest trunk line. Buses and trolleybuses in particular were seen as entry systems that could later be upgraded to rail as appropriate. Although the
Brooklyn system under the BMT built only one trolleybus line, other cities, notably
San Francisco, California and
Philadelphia, Pennsylvania, built larger systems and still maintain "all-four". If you include cable cars as another mode, San Francisco could be called "all-'''five'''," as the
cable cars do provide a general transportation function in addition to being a tourist attraction.
Advantages
New trolleybus near [[Harvard Square, Cambridge, MA]]
Trolleybuses are particularly important in hilly cities, as the electric power is more effective than
diesel in climbing steep hills and trolleybuses' rubber
tires have better roadway adhesion than streetcars' steel wheels upon steel rails. This is especially important in hilly cities such as
San Francisco and
Seattle, USA.
Like other
electric vehicles, trolleybuses are often seen as more environmentally friendly than
hydrocarbon-based vehicles (gasoline, diesel, alcohol, etc.), but the power is not "free", and instead has to be produced at centralised power plants, with its attendant transmission losses. On the other hand, centrally-produced power has the advantage of being more efficient, not bound to a specific fuel source, and more amenable to pollution-control as a single-source supply than individual vehicles, each with its own power generation and each exhausting noxious gases and particulates at street level.
One advantage that is rarely used in other vehicles is that they can generate electric power from kinetic power whilst braking or going downhill, a process known as
regenerative braking.
Another area where trolleybuses enjoy a special niche is locations where
hydropower is abundant and cheap. Examples of this are the extensive trolleybus systems in Vancouver,
British Columbia,
Canada and
Seattle, Washington, USA. The last city doubly benefits, due to the steep road grades near the
Downtown waterfront as well as on
Queen Anne,
First, and
Capitol Hills.
Some have suggested that the trolleybus will become obsolete in a future
hydrogen economy. However direct electric transmission, as used in trolleybuses, is far more efficient (by a factor of two or more) than conversion of energy into hydrogen, transportation and storage of the hydrogen and its conversion back into electricity by fuel cells.
China is experimenting a new form of electric bus that runs without powerlines. This bus runs on power stored in large onboard capacitors, which are quickly recharged whenever the electric bus stops in any bus stop. A few prototypes are being tested in
Shanghai as of early 2005.
Problems with Trolleybuses
Muni Trolleybus crossing tracks of the
San Francisco cable car system]]
As trolleybuses do not follow a track, it is possible for them to come off the route and hence off the electric powerlines above and then get stuck. Some transit systems, such as
Muni in San Francisco, have gotten around this problem by installing battery packs on their trolleybuses to allow them to drive for short distances in case they cannot follow the standard route. Boston is using
dual-mode buses on its new
Silver Line that run on overhead electricity on a fixed right of way and then transition to city streets using
diesel power.
In more general terms, trolleybuses suffer from being "neither fish nor fowl" in current transportation planning. Except in the cases mentioned above where they have special advantages, they have difficulty competing with the efficiencies of
light rail on the one hand, or the flexibility and low start-up costs of conventional buses on the other.
While at one time numerous cities operated this mode of
transport, it is uncommon today in North America and not expanding in Europe, though it is still a common form of transport in the former Soviet republics, generally occupying the niche between street railways and diesel-powered buses.
Trolleys in [[Bratislava]]
Preservation
They are often preserved in museums like the
East Anglia Transport Museum in England.
See also
External links
References
Category:Transportation
Category:Vehicles
de:Oberleitungsbus
fr:Trolleybus
es:Trolebús
nl:Trolleybus
ja:トロリーバス
no:Trolleybuss
pl:Trolejbus
ru:Троллейбус
sk:Trolejbus
sl:Trolejbus
fi:Johdinauto
sv:Trådbuss
tt:Trolleybus
zh:無軌電車