A bi-articulated bus or double-articulated bus and sometimes train-bus or tram-bus is a type of high-capacity articulated bus with an extra axle and a second articulation joint, as well as 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.
Design considerations
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 an increased 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, a bi-articulated bus requires fewer drivers relative to the number of passengers per bus.
Early versions
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 opened in 2004.
Hungarian bus manufacturer Ikarus also developed a bi-articulated bus prototype, the Ikarus 293, in the early 1990s.
In Bucharest, the ITB (today the STB) 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 delivered in 1980, with the rear trailing section coming from a damaged DAC 117E. This vehicle was built to fulfill the need of high capacity person transportation, which was proving difficult for the ITB in 1988, when the prototype was made. However, the DAC 117E's 134 kW traction motor 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, especially the incline between Cișmigiu Park and University Square. 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 2000 when it was fully removed from service, displaced by the then-new Ikarus 415Ts and scrapped. Bucharest no longer operates bi-articulated vehicles (except for trams) due to high traffic levels, which is also the reason why between 2007 and 2018, the RATB refused to operate normal articulated buses. A regular double articulated diesel bus was also made but the capital police refused to allow it to be road legal and to register it on the grounds of its excessive length being outside of the highway code (maximum 17m for articulated buses), and was converted to a regular bus shortly after; the trolleybus was allowed to run being part of a different vehicle class owing to its electric traction.
Use
A bi-articulated bus is a long vehicle and usually requires a specially trained driver, as maneuvering (particularly reversing) can be difficult. Articulated electric trolleybuses can be difficult to control, with their motors producing momentary peak power in excess of 600 kilowatts (816 PS; 805 hp). The trailer section of a "puller" bus can be subject to unusual centripetal forces, which many people can find uncomfortable, although this is not an issue with "pushers". Bi-articulated buses are difficult to reverse park as joints force the bus into a zig-zag shape.