page_title: Trolleybus
section_title: Comparison to motorbuses
hierarchical_section_title: Trolleybus / Advantages / Comparison to motorbuses
caption_attribution_description: Electric bus trolly mechanism, San Francisco Muni - pole support springs and motion dampers. Image by User:Leonard G.
context_page_description: A trolleybus is an electric bus that draws power from dual overhead wires using spring-loaded trolley poles. Two wires, and two trolley poles, are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return path, needing only one wire and one pole. They are also distinct from other kinds of electric buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there are exceptions.
  Currently, around 300 trolleybus systems are in operation, in cities and towns in 43 countries. All together, more than 800 trolleybus systems have existed, but not more than about 400 concurrently.
context_section_description: Better hill climbing - Trolleybuses are better than motorbuses on hilly routes, as electric motors provide much higher static torque at start-up, an advantage for climbing steep hills. Unlike internal combustion engines, electric motors draw power from a central plant and can be overloaded for short periods without damage. San Francisco and Seattle, both hilly American cities, use trolleybuses partly for this reason. Given their acceleration and braking performance, trolleybuses can outperform diesel buses on flat stretches as well, which makes them better for routes that have frequent stops.
  Environmentally friendly - Trolleybuses are usually more environmentally friendly in the city than fossil fuel or hydrocarbon-based vehicles (petrol/gasoline, diesel, alcohol, etc.). Power from a centralized plant, even taking into account transmission losses, is often produced more efficiently, is not bound to a specific fuel source, and is more amenable to pollution control as a point source, unlike individual vehicles with exhaust gases and particulates at street level. Trolleybuses are especially favoured where electricity is abundant, cheap, and renewable, such as hydroelectric. Systems in Seattle and in Vancouver, BC, draw hydroelectric power from the Columbia River and other Pacific river systems. San Francisco operates its system using hydro power from the city-owned Hetch Hetchy generating plant.
  
  Trolleybuses can generate electricity from kinetic energy while braking, a process known as regenerative braking. For regenerative braking to function, there must be another bus on the same circuit needing power, an electric storage system on the vehicle or the wire system, or a method to send the excess power back to the commercial electric power system. Otherwise the braking energy must be dissipated in resistance grids on the bus; this is called "dynamic braking". The use of trolley buses also eliminates pollution during idling, thus improving air quality.
  Minimal noise pollution - Unlike trams or gasoline and diesel buses, trolleybuses are almost silent, lacking the noise of an engine or wheels on rails. Most noise comes from auxiliary systems such as power steering pumps and air conditioning. Early trolleybuses without these systems were even quieter and in the United Kingdom were sometimes referred to as the "Silent Service". This however can also be seen as a disadvantage, with some pedestrians falling victim to what was known as "Silent Death" (in Britain) or "Whispering Death" (in Australia).
  Usable in enclosed space - The lack of exhaust allow trolleybuses to operate underground. In Cambridge, Massachusetts, trackless trolleys survived because Harvard Station, where several bus lines terminate, is in a tunnel once used by streetcars. Although diesel buses do use the tunnel, there are limitations due to exhaust fumes. Also, the trackless trolleys continue to have popular support. The only trolleybus systems in Japan, the Tateyama Tunnel Trolleybus and Kanden Tunnel Trolleybus lines, both run in tunnels serving the Kurobe Dam and Tateyama Kurobe Alpine Route, and were converted from normal diesel buses specifically for their lack of exhaust.
  Longevity and maintenance - Electric motors typically last longer than internal combustion motors, and cause less secondary damage from vibration, so electric buses tend to be very long-lived compared to motorbuses. As the basic construction of buses has not changed much in the last 50 plus years, they can be upgraded such as when air conditioning was retrofitted to many trolleybuses. Such upgrades are often disproportionately expensive. Wheelchair lifts are relatively simple to add; kneeling front suspension is a common feature of air suspension on the front axle in lieu of springs. In comparison to battery-powered buses, the lack of a specially designed battery or fuel cell (typically with expensive patents) decreases the price and weight, and in locations with a sufficient power delivery network, the trolleybus is cheaper and easier to maintain in comparison to charging stations.
caption: Pole bases with springs and pneumatic pole lowering cylinders
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