Alexander Dennis Enviro400

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Alexander Dennis Enviro400
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Years of manufacture 2005 to present
Length 10.4 or 11.5 metres
Width 2550 millimetres
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The Alexander Dennis Enviro400 is a two-axle double deck bus. The chassis was developed from the popular Trident. Metroline in London, England was the launch customer for the Enviro400 in 2005.

On November 4, 2008, a diesel-electric series hybrid version called the Enviro400H was unveiled at the Euro Bus Expo in Birmingham, England.


The modular chassis is made from bolted steel sections and treated with corrosion resistant two-pack epoxy. The body is constructed from aluminum extrusions with stainless steel reinforcement and is integrated with the chassis using clean frame joints. The dissimilar metals are treated with dielectric paint to prevent corrosion. The side panels are aluminum which are bonded to the frame. The roof structures are one-piece composite panels. Polymers are used for the front and rear faces.

The Enviro400 chassis can be fitted with bodywork from other suppliers. Likewise, the Enviro400 body can be fitted onto the Volvo Buses B9TL and the Scania N230UD chassis. There is one example of an Enviro400 body fitted on a Volvo B7TL chassis before the introduction of the B9TL.

Coincident with Euro 5, the Enviro400 chassis was revised with the radiator on the offside and the engine on the nearside. The engine was originally mounted on the offside due to the layout of the ZF rear axle. A new axle layout allowed for a simplified straight angle drive. The revised Enviro400 also has an additional 50 millimetres of ground clearance.[1]

A facelifted Enviro400 body debuted at the 2009 Coach & Bus Live. A line of white LED lights was incorporated under the existing headlights, and new curves were added on the front bumper.

The first Enviro400 buses to operate in Hong Kong (for Citybus and Kowloon Motor Bus) were delivered in 2009. They feature a large HVAC system and the updated front fascia. Further exports of the Enviro400 were made to Canada and the United States, however only as an open-top sightseeing bus. One of the first orders was placed by E Noa Tours of Honolulu, Hawaii who took delivery of 10 buses in 2012. The front and rear of the export variants' top deck share the design of the Enviro500 respective of region.

The Euro 6 Enviro400 was introduced in May 2014 and features a new look, new heating and ventilation system, new glazing system, decreased weight, and increased seating capacity. Under a Major Model Change project, Alexander Dennis worked with over 70 operators in a three-year period to improve the design of the Enviro400.[2]

The updated Enviro400 continues with the curved and sloping front end. A new headlight cluster flows into the windshield and the front and rear bumpers are accented by a cut-out at the bottom. Glazing on the front and rear is flush-mounted to the body instead of gasket mounted as previously used. The rear around the engine flares outward gently. This is evoked on the front around the destination sign and windshield.

The interior was redesigned with elements to improve ergonomics and appeal for both passengers and drivers. The bus is able to seat one more person in a London configuration, five more in the hybrid model, and seven more in the full-length model. The bus now features Alexander Dennis's L-shaped "Square-case" staircase. The electrical system is housed within the body structure and is composed of modular sections for easier replacement.

The updated Enviro400 features Alexander Dennis's Quick Release Glazing (QRG) system. The window frame is attached to the body with its face flush with the body panels, and the glass is retained against the frame by a removable retainer. This allows the glass to be removed from inside the vehicle instead of from an external platform.[3]

While the previous frame was welded, the new Enviro400 uses mechanical fasteners. In addition, high stress areas now make uses of stainless steel. To reduce weight and increase stiffness, the roof and interdeck use one-piece composite panels.

In 2016, Alexander Dennis introduced SmartPack. This is the management of the alternator and air compressor where they only charge during deceleration when they place no additional load on the engine. SmartPack also includes stop/start technology and electrically-driven cooling fans. The following year, Alexander Dennis introduced their SmartHybrid. The 48 volt mild hybrid system recovers kinetic energy during deceleration, stores it in supercapacitors, and then uses it to assist the bus in acceleration.[4]

Enviro400 City

At Coach & Bus Live 2015, Alexander Dennis launched the Enviro400H City (hybrid). It is aimed at the London market and was developed in collaboration with Transport for London (TfL). TfL approached various bus manufacturers to design a bus that built upon the design of the New Routemaster. A conventional diesel-powered version designed for systems outside London was unveiled the following year. Blackpool Transport was the first to purchase the Enviro400 City, taking ten 10.5-metre high specification buses.[5]

The Enviro400 City draws its aesthetic from the new Enviro200 and New Routemaster. It has a rounder appearance, evoking the iconic Routemaster, and has a fully glazed staircase.[6] Inside, the bus may feature upscale style and appointments like high-back leather seating and tables.


In November 2018, Alexander Dennis unveiled the 13.4-metre, tri-axle, Enviro400XLB. It is built on the Volvo Buses B8L chassis and was developed in close collaboration with Lothian Buses and Volvo. The bus can seat 100 passengers in total and brings extra capacity to busy routes in Edinburgh, Scotland. The 42 buses built for Lothian Buses feature high-backed seating, wifi, USB charging, mood lighting and audio-visual stop announcements. While the Enviro400XLB has three axles like the Enviro500, the two buses have a different body structure.[7]

Specifications (on Enviro400 chassis)


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  1. Euro 5 Enviro400,, retrieved on 2009-09-11
  2. The all-new Enviro400 – designed by the industry for the industry. Alexander Dennis. 01 May 2014. Press release. retrieved on 03 May 2014.
  3. Patent WO 2013156802 A1
  4. ADL wins Scottish Transport Award with SmartPack and SmartHybrid technology for efficient diesel Low Emission Buses. Press release. Alexander Dennis. 15 June 2018.
  5. Blackpool sets the pace with £2m Enviro400 City bus deal. Press release. 18 January 2016. Alexander Dennis.
  6. Deakin, Tim, and Tim Deakin. 'ADL Gets The London Look'. N.p., 2015. Web. 30 Sept. 2015.
  7. 100 seats for Lothian in new three-axle ADL Enviro400XLB on Volvo chassis. Press release. 08 November 2018. Alexander Dennis.