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A bi-articulated bus or double-articulated bus is a type of high-capacity articulated bus with an extra axle and a second articulation joint that allows it to carry three passenger compartments. Due to the extended length, bi-articulated buses tend to be employed in high-frequency core routes or bus rapid transit schemes rather than in conventional bus routes.
Common bi-articulated buses resemble rail vehicles in design. They often have elevated train-type doors instead of traditional bus doors to use dedicated stations. Payment is typically made at a bus station using a fare gate rather than on the bus.
Compared to using multiple smaller buses on a route, challenges using a bi-articulated bus include:
- difficulties maneuvering in traffic
- a reduced turning radius
- the need to have extended length station platforms
- reduced frequency of service (one larger bus every 10 minutes rather than two regular sized buses coming once every 5 minutes)
- less flexibility for scheduling, routing, and maintenance.
However, the bi-articulated bus requires fewer drivers.
In the late 1980s, the French manufacturers Renault and Heuliez Bus developed the "Mégabus" (officially the Heuliez GX237), a bi-articulated high-floor bus. 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, were used on Bordeaux's bus route 7 until the city's tram system was built in 2004.
In Bucharest, ITB (today RATB) operated a double articulated trolleybus (unofficially called DAC 122E), made by adding a modified section between the first and the last sections of a DAC 117E articulated trolleybus. This vehicle was built to fulfill the need of high capacity person transportation. However, the DAC 177E's 125 kW proved insufficient for such a heavy vehicle, let alone the weight of passengers when it operated at full capacity. As a result, the vehicle was very slow and had trouble operating on grades. It also had trouble making sharp turns and was difficult to control, especially on snow or ice. This trolleybus was operated on long lines with wide roads and no major turns except the end of the lines like 69 and 90, but occasionally entered on lines 85, 66, 79 and 86. Bucharest traffic became increasingly intense in the very late 1990s, and RATB sought shorter trolleybuses. The DAC 122E was withdrawn from regular service, being occasionally used on lines 69 and 90 until the mid-to-late 2000s when it was fully removed from service and scrapped. Currently, except double articulated trams V3A and simply articulated V2A T trams, RATB operates no more articulated vehicles due to traffic levels.
The transit system that has used bi-articulated buses the longest is the Rede Integrada de Transporte, in Curitiba, Brazil, which provides a type of service that has come to be known – particularly in American English – as bus rapid transit (BRT), where buses run in dedicated lanes and stop only at enclosed stations. Use of bi-articulated buses began in 1992, with vehicles manufactured by Volvo (chassis) and Marcopolo/Ciferal (body), able to carry up to 270 passengers. Each bi-articulated bus is equipped with five doors where passengers can quickly load and unload. Buses stop only at enclosed, tube-shaped stations, where passengers pre-pay the fare and then board at the same level as the vehicle floor. Curitiba has over 170 bi-articulated buses in operation on routes serving five main corridors of dedicated bus lanes. These buses run on an average period of 50 seconds during peak hours.
The Brazilian bus body manufacturers Marcopolo, CAIO, Busscar and most lately Neobus have made many bi-articulated buses on top of Volvo chassis. They are currently used in Rio de Janeiro, São Paulo, Campinas, Goiânia, Curitiba and Bogotá.
Volvo has manufactured several bi-articulated buses now in use in Gothenburg. They are based on Volvo's "puller"-type articulated, low-floor bus model with the internal combustion engine mounted on the floor on the side of the bus, and the cooling system on the roof. They have not manufactured anymore and are currently being replaced by normal articulated buses.
The Belgian manufacturer Van Hool offers a 25 metres (82.0 ft) bi-articulated bus with a capacity of about 180 passengers. In September 2002, fifteen were deployed on lines 11 and 12 in the Dutch city of Utrecht, connecting the downtown railway station to office, college and university buildings at the edge of the city. Twelve more have been added since. These buses are also used in the German cities of Aachen (lines 5 and 45) and Hamburg (Metrobus 5 and Eilbus E86), where single-articulated buses alone were not able to handle the huge number of passengers per day.
Swiss manufacturer Hess produces a bi-articulated trolleybus called LighTram that is in use in several Swiss cities, including Zürich, Geneva and Lucerne. Also, a bus with a hybrid engine based on the LighTram is offered. This type is currently in use for the Luxembourgian bus operator Voyages Emile Weber. From August 2014 to 2016, bi-articulated LighTram busses were in service in Groningen, Netherlands on the route from the main train station via the city center to the university north of the city. In 2016 these busses were moved to Utrecht because the few stops and higher speeds on this line made the hybrid engine perform poorly.
In 2012, Fraunhofer IVI introduced the AutoTram Extra Grand in Dresden. With overall length of 30.73 metres (100.8 ft) it is the longest bus in service with a passenger capacity of 256. Its unique 5-axle design is made possible using advanced computer controlled steering on the 3 trailing axles.
A Chinese manufacturer Zhejiang Youngman (Jinhua Neoplan bus company) developed the JNP6250G bi-articulated bus for 300 passengers with assistance from NEOPLAN Bus GmbH. In 2007, these buses appeared on trial service in Beijing and were thought to be the world's longest (25 meters long).
In November 2016, Volvo launched the Volvo Gran Arctic 300 bi-articulated bus chassis, specifically developed in Brazil for BRT systems. At 30-meter long, this chassis is capable of carrying 300 passengers.
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