Multi-axle bus

A tri-axle coach, the Neoplan Skyliner

A multi-axle bus is a bus or coach that has more than the conventional two axles (known as a twin-axle bus), usually three (known as a tri-axle bus), or more rarely, four (known as a quad-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 implement trailer buses.