Bi-articulated bus

A bi-articulated bus or double-articulated bus is a higher-capacity type of articulated bus. It is an extension of a conventional or single-articulated bus, in that it has three passenger compartment sections instead of two. This also involves the addition of an extra axle and a second articulation joint. Due to the extended length, bi-articulated buses tend to be used on high-frequency core routes or bus rapid transit schemes rather than conventional bus routes.

Although buses can be designed any way regardless of the number of articulations, common bi-articulated bus designs resemble rail vehicle ones—in terms of how it operates—more than standard buses; in particular, considerations such as rapid passenger entry/exit (train type doors—usually elevated) vs. the traditional bus doors (with steps, including kneeling bus) often found on extra long traditional buses. By pushing payment issues (and their delays) to a BRT bus station, and physically separating paid passengers by fare gates, and eliminating passenger or bus vertical movement to get on/off the bus, it frees the conductor from delays and complications, increasing throughput, speed, and schedule reliability. The trade-off however is the cost of building bus stations vs. simply a marking or pole to indicate where stops are. Other issues include turning radius and drive control.

An additional advantage is that they reduce the number of drivers needed to run a service for a specific number of people — i.e., for areas with relatively high labor costs, it is usually much more cost-efficient to run bi-articulated buses with one driver over running two smaller rigid buses providing the same total number of seats. For traditional bus routes without stations and with driver managed payment systems, this is the biggest advantage.

Disadvantages include some difficulties in traffic, the need to have bus stops catering to the extended length, and the fact that two buses with the same capacity can be used more flexibly, such as having one bus arrive every five minutes, instead of one of the larger articulated buses every ten minutes (as an example providing the same service capacity, but different frequencies), or covering for other existing bus routes.

The French manufacturers Renault and Heuliez Bus developed the "Mégabus" (officially the Heuliez GX237), a bi-articulated high-floor bus, in the late 1980s. The demonstrator Mégabus visited transit agencies throughout France, but the only city to order them was Bordeaux (an order of 10 buses, built in 1989). These buses, now retired, operated Bordeaux's bus route 7 (the most heavily used route in Europe) until the city's tram system was built in 2004.

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