thumb|Boston [[Neoplan USA|Neoplan DMA-460LF dual-mode bus, operating in diesel mode (with its trolley poles lowered)]]

thumb|Esslingen dual-mode bus of the type Mercedes-Benz O 405 GTD, also operating in diesel mode.

A dual-mode bus, also known as a duobus or bimodal bus, is a bus that can operate using two independent power sources. Most commonly, this refers to a vehicle that combines the features of an electric trolleybus, drawing power from overhead lines, and a conventional bus, powered by a diesel engine.

The term is primarily used for buses with two full-fledged, powerful propulsion systems, designed for regular service on routes that are only partially equipped with overhead wires. This distinguishes them from trolleybuses equipped with a small auxiliary power unit (APU), which is only intended for short-distance, low-speed maneuvers such as bypassing obstacles or navigating depots.

Disadvantages

Despite their flexibility, dual-mode buses have several drawbacks that have limited their widespread adoption. The inclusion of two complete powertrains (an electric motor and control systems, plus a diesel engine, fuel tank, and transmission) significantly increases the vehicle's weight. For example, the electrical equipment on a Mercedes-Benz O 405 GTD added six tons to its weight. This extra weight leads to higher energy consumption in both modes of operation.

Dual-mode buses are also more expensive to purchase and maintain than either a standard trolleybus or a diesel bus. The complexity of the dual systems can lead to lower reliability and higher maintenance costs. The space required for the additional equipment can also reduce passenger capacity, impacting the vehicle's economic efficiency.

List of models

Excluding early precursors, a total of 438 series-production dual-mode buses have been built. The vast majority of these were articulated vehicles.

  • Boston, Massachusetts, USA: Used 32 Neoplan AN460LF buses on the Waterfront portion of its Silver Line from 2005 to 2023. Electric power was used in the tunnel under the Fort Point Channel, while diesel power was used for surface streets and the Ted Williams Tunnel to Logan Airport.
  • Esslingen am Neckar, Germany: One of the pioneering systems, operating various Mercedes-Benz models from 1979 until 2008.
  • A hydrogen-powered bus was developed by Tokyo City University in 2009. It received a license plate from the Ministry of Land, Infrastructure, Transport and Tourism, becoming the first hydrogen engine bus in Japan to be legally permitted to operate on public roads. It was used as a shuttle bus between the university's campuses.

See also

  • Electric bus
  • Electro-diesel locomotive, the railway equivalent
  • Guided bus
  • Hybrid electric bus
  • IMC Electric bus
  • List of buses

References