The Alexander Dennis Enviro300 (previously known as the TransBus Enviro300) is a light-weight full size single-deck bus built by Alexander Dennis (previously by its predecessor TransBus International) in the UK since 2001. The design was the first of the new Enviro range of buses from TransBus and also the first bus to be built as an integral bus by TransBus. The Enviro300 was introduced in order to fill a gap in the manufacturer's product range. At the beginning the Cummins ISBe220 5.9 litre Euro III engine was provided as standard, but for Euro IV and V, the engine is the 6.7 litre ISBe with 225 hp for Euro IV and 225 or 250 hp for Euro V. There is a choice of 3 gearboxes: ZF 6HP504C (originally 5HP502C), Allison T280R and Voith D854.5 (originally DIWA854.3E). It was developed to compete