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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.
In Romania, ITB (today RATB), operated a double articulated trolleybus, fleet number #7091, which was in fact produced by URAC and not by ROCAR (Ex Autobuzul or Tudor Vladimirescu Factories), by simply adding a modified section between the first and the last sections to a DAC117E articulated trolleybus. It was unofficially called DAC 122E. This vehicle was built for the need of high capacity person transportation, and it is rumored that two more vehicles were built, but only one (7091) entered and remained in service for a period of time. The other two vehicles were (it was rumored) reconverted to single articulated trolleybuses DAC117. The main problem encountered with this vehicle was the fact that it had the engine of a DAC 117E with only 125 kW, which proved insufficient for such a heavy vehicle (not taking into account that it was extremely overloaded when operated at full capacity), therefore the vehicle was very slow, encountered problems steering and it was difficult to be controlled especially on snow or ice. It was also having trouble operating on grades. Also, turning the vehicle in narrow areas was a challenge. While the traffic in the early 80's when it was designed and built and the end of the 90's was not very intense, this trolleybus was operated on long lines with wide roads and no major turns except end of the lines like 90 and 69, but occasionally entered on lines 85, 66, 79 and 86. It was scrapped somewhere in 2000, because when RATB renewed its park, they withdraw most old DAC 117E and 217E from most central lines in order to increase speed, and shorter trolleybuses were achieved. Also, the traffic in Bucharest became increasingly intense in the very late 90's, therefore such a vehicle would cause traffic jamming, therefore it was withdrawn from regular service, and until it was scrapped, it was occasionally sent on 69 and 90 until mid-to-late 2000 year when it was definitively withdrawn from service and scrapped. However, conventional DAC117E and 217E continued their service until 2008 on many peripheral lines, but occasionally entering service in central lines. Currently, except double articulated trams V3A and simple articulated V2A T Trams, RATB operates no more articulated vehicles, due to traffic levels.
It was also rumoured that ROCAR (Autobuzul) made a double articulated DAC bus, but nothing is confirmed, as there are no official photos or prospects (while even for prototypes, ROCAR Autobuzul was issuing prospects and flyers), therefore the existence of a double articulated DAC Bus is uncertain. As said before, the only double articulated DAC 117E based vehicle was manufactured by ITB (RATB) - URAC.
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 are 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 bi-articulated LighTram busses are in service in the 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.
The Chinese manufacturer Zhejiang Youngman (Jinhua Neoplan) has developed a 300-passenger, 25 metres (82.0 ft) JNP6250G bi-articulated bus, deemed the "world's largest", with assistance from NEOPLAN Bus GmbH. These buses are on trial service in Beijing.
In November 2016, Volvo launched the Volvo Gran Artic 300. It has been developed in Brazil to operate on bus rapid transit systems. It will be 30 metre long and have capacity to carry 300 passengers.
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