Multi-axle bus

Main article:Bus

Amulti-axle busis abusorcoachthat has more than the conventional twoaxles(known as atwin-axle bus), usually three (known as atri-axle bus), or more rarely, four (known as aquad-axle bus). Extra axles are usually added for legal axle load restriction reasons, or to accommodate different vehicle designs such as articulation, or rarely, to implementtrailer buses.

A tri-axle coach, theNeoplan Skyliner

History

An early example of a multi-axle bus was a one-off three-axleCrossleyCondor,shownhere,built for the 1932 Scottish Bus Show.

Reasons for multiple axles

TheBedford VALtwin steer coach, whose extra axle allowed for smaller lighter wheels and a lower floor height

Usually vehicle licensing authorities of different countries will set legal limits on the amount of weight that can be put on each axle. In theUK,a recentextension to the legal limit on the length ofrigid busesandcoacheshas led to the increased use of three axles to accommodate the heavier chassis and passenger load. Certain countries apply exceptions to vehicle rules for specific operations.

Extra axles may also be provided on shorterbusesandcoachesto accommodate extra equipment loads, such as passenger lifts, or comforts such as toilets, televisions, climate controls. In addition, in some cases the need is bus cargo transport, when large cargo compartments and heavy weight of cargo needs extra axles.

Adding axles to chassis designs is done for specific reasons such as weight or legalities, as having extra axles means extra costs for the operator in terms oftyrereplacement, and to an extent, higherfuel consumption.

Rear axle steering

In some buses the rearmost axle is connected to thesteering,with the rear most set steering in the opposite direction to the front axle. This steering arrangement makes it possible for the longer triple axle buses to negotiate corners with greater ease than would otherwise be the case.

Rigid chassis

East LancsbodiedVolvo B9TLtri-axledouble-decker busin theUnited Kingdom

ANeoplan MegalinerQuad-axle coach atTsukuba CenterinJapan

A bus with a single, rigid chassis, is known as arigid bus,as opposed to anarticulatedorbi-articulated bus.

Tri-axle

Tri-axle rigid buses can either betag-axle busesortwin steer buses.

Atwin steer busis a rare type of tri-axled bus; where the double axles are in the front and steer, as in theBedford VALorBustechCDi.

By far the most common type of tri-axle rigid bus is thetag-axle buswith one axle at the front for steering, and two axles at the back; the main drive axle and a trailing non-drive axle.

Tri-axledouble-decker busesare common in high capacity operating environments where articulated buses are not used, such asHong KongandSingapore.Tri-axle buses also see high volume use inDublin, Ireland.Imported tri-axle buses were used initially byMegabusfor high capacity low cost intercity travel in the UK.

Tri-axle double decker coacheshave been used to accommodate the extra weight. Models are also being introduced on high capacity inter-city routes, such as by the operatorMegabus.

Quad-axle

TheNeoplan Megalinerwas the firstquad axle double decker coach,and is used inJapan.Further examples include theScania K380IB 8x2.

Articulated chassis

A tri-axletrailer bus

Tri-axle is the standard arrangement of two-partarticulated buses.

Quad-axle arrangement is sometimes employed on articulated buses to accommodate the extra weight of coach bodies, such as in this quad-axle articulated coachVolvo Articulated Coach,and the quad-axle double-deck articulated coach, theNeoplan Jumbocruiser.Quad-axle arrangement is also the exclusive arrangement for three-partbi-articulated buses.

A rare reasonwhy a bus may have multiple axles is in the case of atrailer bus,where the bus passenger cabin is built as a bodysemi-trailertowed by a separatetractor unit.

See also

• BRTS
• Bus
• Coach (bus)
• List of buses
• Trailer bus