Alexander Dennis Enviro400

London operator Metroline was the first company to order the Enviro400, ordering 28 for route 24 in June 2005, entering service at the end of the year.[2] One dual door demonstrator, named "Spirit of London", was delivered to Stagecoach London to replace the Dennis Trident destroyed during the 7 July 2005 London bombings[3] and a single door demonstrator was delivered to the then Travel West Midlands for evaluation. Both prototypes were exhibited at Coach & Bus Live 2005 in the National Exhibition Centre in Birmingham.[2]

The Enviro400 had sold well in London with a number of operators, such as Travel London and London General (which received the first Euro IV-engined Enviro400 in May 2006), operating these buses. It is also popular with Stagecoach, which placed its first order of 130 low-height models in February 2006, later followed by another 389 buses with Euro IV/V engine. Arriva also received Enviro400s for its UK operations, Arriva Merseyside relaunched its Wirral - Liverpool 'Cross River' services with a batch of 23 in January 2009. A further batch of 12 was allocated to Bootle depot in September 2009 originally for the cross-Liverpool trunk service 60 linking Bootle with Aigburth. However a much larger order of 128 Enviro400s was placed by Arriva for its Merseyside division from the Autumn of 2014 onwards with significant numbers in service at Bootle, Green Lane, St Helens, Southport and Speke depots.

On 13 October 2006, Solent Blue Line received a Volvo B7TL/Enviro400 meeting the Euro III emission standard, with the interior in Wilts & Dorset livery. This remains a one-off as all subsequent Enviro400s on Volvo chassis were built on the B9TL chassis. An Arriva demonstrator was shown at Euro Bus Expo in 2006 to the latter standard.

East Yorkshire Motor Services took delivery of five Enviro400-bodied Volvo B9TL in December 2007, which entered service in January 2008. London General also received three Enviro400-bodied Volvo B9TLs in October 2008, which are being evaluated against integral Enviro400s and Wright Eclipse Gemini-bodied Volvo B7TL/B9TLs that are extensively featured in Go-Ahead's London Central/General fleets.

Stagecoach announced on 28 February 2007 that it had ordered 25 Enviro400s with Scania N230UD chassis, which were subsequently delivered in early 2008. These were followed by another 56 for delivery in 2009, 100 for 2009/10, 100 for 2010/11, 91 for 2011/12 and 57 for 2012/13. Oxford Bus Company and Wilts & Dorset also received some examples.

A hybrid version, the Enviro400H, entered service with a number of operators including Metroline, East Yorkshire Motor Services, National Express West Midlands, Reading Buses, Stagecoach London, Lothian and First Glasgow.

In 2008, one Enviro400 was built for the 2008 Summer Olympics and 2008 Paralympic Games as a handover bus.

In 2012, Southern Vectis received 20 for school contracts on the Isle of Wight. These were delivered during late December 2012 and early January 2013 and entered service on a wide variety of school services on the island from 7 January 2013. Southern Vectis then proceeded to order another 16 Enviro400s to be used on public routes, mostly route 9, with the first six going to Oxford Bus Company for a few months. Ten of these buses have been delivered and on 3 January 2014, they commenced operating.

Between 2014 and 2015 Arriva North West received a total of 128 integral Enviro400s for a number of services on Merseyside - with 28 arriving in 2014 and the remainder being delivered between January and July 2015. Arriva Buses Wales received a total of 29 high specification Enviro400s between June 2014 and March 2015 for deployment on two new Sapphire services between Rhyl and Llandudno and Chester and Connah's Quay respectively.

Stagecoach is currently receiving a total of 76 Enviro400s for services with Stagecoach London, Stagecoach North West and Stagecoach South West.

Irish state run operator Dublin Bus was the first bus operator to order the Volvo B9TL-based Enviro400, ordering 50 with the first of these entering service on 14 August 2007, later followed by another 50.

A Kowloon Motor Bus Enviro400 in Mong Kok, Hong Kong.

Alexander Dennis Enviro400 (with Enviro400 MMC-style front and rear) of NWFB in Hong Kong.

In 2009, Kowloon Motor Bus and Citybus of Hong Kong received two (one for each operator) air-conditioned Enviro400 for evaluation, both of which entered service in February 2010. Citybus introduced one more in July 2010.

In November 2010, Alexander Dennis had confirmed an extra order of 38 Enviro400s from Citybus at the press conference of Euro Bus Expo 2010 held in Birmingham, UK; these buses entered service in 2011. A further order of 20 Enviro400s had been placed and these buses started to enter service in 2013.

MTR Corporation also ordered nine Enviro400s for MTR Bus service, these buses entering service in 2012. Two more Enviro400s entered service in 2018.

Kowloon Motor Bus received a further 50 Enviro400s between 2012 and 2013.

New World First Bus ordered 60 low-height Enviro400s, these entered service in 2016 and 2017. New Lantao Bus ordered 14 low-height Enviro400s, which are similar to New World First Bus' batch. They entered service from October 2018 and have served route 3M since January 2019.

Open Loop New York Enviro400 open top bus in New York

The Enviro400 was introduced to North America exclusively as an open-top bus for sightseeing purposes. It is not available as a public transport vehicle, unlike the similar Alexander Dennis Enviro500.

On 11 November 2010, Alexander Dennis announced it had received an order for 10 Enviro400s from Coach USA subsidiary Twin America, in New York.[4]

Upper deck of the Enviro400

The Enviro400 features an innovative seating layout that maximises use of seating space on the lower deck by placing two forward-facing moulded seats onto the front nearside wheelarch box with a small luggage shelf on the rear half, and also (on full-height models) a single forward-facing moulded seat on the front off-side wheelarch hub between the driver's partition and the staircase.

The engine is a six-cylinder Cummins driving through a Voith or ZF automatic transmission. The maximum speed is 80 mph (130 km/h). A hybrid-electric version of the powertrain was also available.[5]