ADL Enviro400: Designed by the industry, for the industry

It’s taken two years and a unique 7.5m development programme involving 70 operators. The all-new Euro 6 ADL Enviro400 is here, offering a lighter weight and an all-new design with more seats, and is promised to be ADL’s most reliable bus.


The headline is simple: The all-new Enviro400 is designed by the industry, for the industry.

The most thoroughly engineered bus ADL has ever built, it is lighter, more fuel efficient, and has more seats, a “radical” new heating and ventilation system, plus a patented quick-release system that reduces glass replacement time from three hours to three minutes.

Says Alexander Dennis Limited (ADL) CEO Colin Robertson: “Welcome to the future.”

This week the bus – in London and provincial versions – will be unveiled at ADL’s Larbert HQ in a series of presentations to suppliers and operators, and is the culmination of two years’ hard work, with operators very closely involved.

“Innovation with style” is the design and engineering philosophy that has been pursued relentlessly by ADL in the 10 years since the company’s inception, says Mr Robertson, and the all-new Enviro400 is no exception to that rule. “It is an inspired successor to Britain’s best-selling double-deck over the past decade.”

The Enviro400 has been meticulously thought-out and built as part of a unique partnership involving ADL’s design and engineering teams, customers from across the industry and suppliers with unique, specialist skills.

“This visionary, collective approach has resulted in a bus designed by the industry, for the industry,” Mr Robertson adds.

It is 400kg lighter, 12% more fuel efficient (according to official Millbrook tests), quieter, environment-friendly and has increased seating capacity – up to seven more seats in the full-length model. It is class-leading in a vast range of ways, incorporating 200 improvements that introduce a wealth of benefits for operators, drivers and passengers.

Major model change

Code-named MMC (standing for major model change), the new bus is designed to exceed all operator expectations. It is also the result of a remarkable study of every fault reported on every ADL two-axle double-decker since 2006.

“MMC, simply stated, is the future of our business,” says Mr Robertson. “It’s the most phenomenal opportunity to underpin the business from 2014 onwards. It will take our business to the next level.”

More than 70 operators were involved in a two-year customer engagement initiative at the heart of the vehicle’s development programme. As a result the new Enviro400 incorporates an impressive list of improvements. Early in the project it became clear that listening to operators’ feedback – and learning from their wealth of experience – on the existing Enviro400 was “vital to the development of MMC.

“What we’re doing is making sure that we absolutely understand the wants and needs of our key customers,” says Mr Robertson.

Adds ADL International Business Development Director Robert Davey: “One of the objectives we have is to demonstrate to customers that the whole-life cost of owning our vehicles is measurable and lower and cheaper than that of the competition.”

In the third stage of the project, in spring 2013, a physical mock-up of the front saloon and driver’s cab – plus a digital mock-up of the interior of the bus – was revealed to operators at ADL’s Skelmersdale development centre. At the time, representatives from operators praised ADL’s involvement of them from an early stage. The overwhelming feedback was that they were pleased that ADL had listened and taken on their ideas about the new design.

Mr Robertson admits that involving operators so early and so deeply in the project was a risk, as it meant information could pass to competitor manufacturers, but he is confident that the gamble was worthwhile, given the outcome.

The final part of the customer engagement jigsaw came in late 2013 when operators were invited to Larbert – ADL’s new HQ, which it moved into a few months previously. It houses offices, the boardroom, the parts export centre and a large vehicle development centre for prototyping work. Here operators saw the prototype vehicle before it went to Millbrook, Bedfordshire, for extensive testing.

Stylish new look

The Enviro400 has a stylish new look with a modern curved shape that flows from back to front, descending onto distinctive ‘hips’ at the rear, while the interior, both upstairs and downstairs, has been designed to ensure that shapes, colours and materials blend together, all of which has been achieved without compromising leg room or seat size.

The external design also reduces dirt traps, for example around the fuel filler cap, while the lower panels have a quick-release system for rapid replacement. The corner panels are also quickly replaced and are in smaller sections to reduce the cost.

New rear keeps back window and introduces 'hips' in external styling
New rear keeps back window and introduces ‘hips’ in external styling

Yet, despite all of these demands there is one more seat on a stan-dard 10.3m London bus (70 seats), five more on a hybrid, and seven more (86 seats) on a full-length 11.5m single door diesel.

Maintenance eased

Access and ease of maintenance is also much-improved throughout the new Enviro400.

It is powered by a Euro 6 Cummins 6.7 litre engine, which has been in field trials with operators for nearly two years.

The tailgate to the engine compartment at the rear of the bus opens higher, while the side doors to the power unit open wider and, if necessary, can be removed entirely.

Nearside rear access opening to engine bay. Door can be removed
Nearside rear access opening to engine bay. Door can be removed

The electrical system is also all-new, based on a fully multiplexed design and is housed in one well-arranged, easily reached distribution centre located in the upper deck.

Similarly, the wiring system is radically different with shorter, modular sections that can be changed and clipped back into place easily. The wiring has also been carefully chosen to maximise resistance to heat and corrosion, while the entire system is contained inside the body of the vehicle rather than being exposed to dirt, moisture or impact damage.

Electrical system: New single location
Electrical system: New single location

Likewise, there is improved access to the new wiper motor and the aluminium fuel tank, which can be removed from inside the bus, and the destination display – now on a pivot mounting – can be reached effortlessly, making cleaning and maintenance far quicker. The doors and ramps are also new, reliable designs.

The suspension system now has electronic control to stop buses ‘settling’ when parked and the air system has been modified to stop leaks. The body is structurally stiffer, helped by bonded front and rear screens, eliminating water leaks. The upper-deck break-glass rear emergency window is flat glass, to save replacement cost, with a separate curved GRP section above.

Radical glazing

One of the most contentious areas within bus design is the side
glazing. Gasket glazing is still preferred by many operators due to the relative speed of replacement, compared with bonded glazing, which has long cure times.

Neither is ideal, says ADL, which has patented its quick release glazing (QRG) system. This flush, leak-free system is a major time saver. Damaged windows can be replaced on the spot, and the bus back on the road within minutes.

Patented quick release glazing system takes three minutes to fit glass
Patented quick release glazing system takes three minutes to fit glass

An aluminium frame is part of the body structure, adding to stiffness and ensuring that the windows don’t vibrate at tickover.

The external appearance is much improved, but the real benefit is in the interior where the appearance is identical to that of a bonded vehicle, with plastic cappings. The glass is held in place by plastic trim strips, which are quickly levered off. However, the glass remains firmly fixed with screw-fixed blocks, discreetly fixed under the trim. These are removed with a special tool, and importantly the entire glass removal and replacement process can be carried out by one person, from inside the bus. This means that no restraints, harnesses or access scaffolding/platforms are needed.

In a demonstration to the press a fitter, who had only once previously replaced a window, demonstrated that indeed it would only take three minutes to change a window, and with minimal tools. We have no doubt that on-the-road repairs are perfectly practicable and feasible.

Passenger experience

Passengers will enjoy a whole new experience when they board the Enviro400. They will be struck immediately by the light, airy and welcoming ambience of the interior, an environment enhanced by large windows and the gloss finish of the internal panels that flow seamlessly from the driver’s cab into the seating areas.

More seats in all versions
More seats in all versions. Light and airy feel

Every detail has been examined, debated and deliberated upon, such as the inclusion of the rear window, which operators universally agreed was a ‘must have’. Also, the side windows are large, while the flat floor to the rear set of seats and lack of seating runners on the floor make for easy access and cleaning.

The pair of seats at the front by the driver have been retained, while the new staircase and fuel tank design means that the single seat behind the driver has been omitted. All are full-size seats, and the moulded ones have been redesigned to eliminate the GRP edges.

Flowing lines from driver's cab to stairs and high-gloss panels
Flowing lines from driver’s cab to stairs and high-gloss panels

Smooth panels, from the flow of lines from the driver’s cab to staircase, cove panels and concealed LED lighting make the saloon appear spacious and welcoming.

Features ranging from cab door locks and seals, to hand-pole mountings and secure wiring looms have been re-examined and reinvented, all in pursuit of the industry’s Holy Grail, the rattle-proof bus.


Rather than a staircase, what ADL is calling its “revolutionary square-case” has been introduced. This compact, square design takes up less space, is easier to use and is brightly lit, making it safer and more user-friendly, thanks to a continuous handrail running from top to bottom.

The staircase in the provincial version
The staircase in the provincial version

Heating and ventilation is one of the most contentious subjects in the bus industry.

ADL engineers have made profound changes. These are based on a new approach that incorporates a heating unit located in the lower saloon. This forces air to all corners of the bus quickly and efficiently, providing a constant temperature throughout, and reducing condensation in winter.

When supplemented by an upper-deck air chiller it can also contain the temperature to 17-18C, ensuring that passengers remain warm in the winter and cool in the summer months.

Driving force

Drivers too have played a vital part in the design and layout of the Enviro400, particularly in determining the size, shape and layout of the cab area.

Drivers’ representatives from across the country were an integral part of ADL’s customer engagement programme and contributed enormously to the creation of a cab that is designed for maximum comfort, safety, efficiency and ease of use. The assault screen at the point of entry is no longer an adjunct to the design.

It is an integral part of the whole approach being functional but blending impeccably with the surrounding area. There’s a large space for the ticket machine, while the all-new cab door has seals and a re-engineered lock specifically designed to be rattle-proof.

Inside, the cab area is spacious (thanks in part to moving the electrical boards to the top of the stairs) and distracting reflections are eliminated by the attention to detail, while visibility is further improved with a new wrap-around windscreen, improved sight lines to the front and sides, and well-positioned mirrors.

The switch-gear is all-new too, adopting the rocker-type positive feedback buttons overwhelmingly favoured by drivers and operators, while the fully adjustable steering column for height and reach (with which the binnacle also moves) and Chapman’s seat ensure that everything the driver needs is comfortably within reach.

Driver feedback: New positive action switches
Driver feedback: New positive action switches

Increasing technology often means that many bus cabs today are bedecked with screens, some vital and some optional, but often appearing disorganised. Working with operators and drivers, the ADL team has designed an ingenious layout for screens that is practical, easily reached and unobtrusive.

There is also a handy, sizeable storage area for the driver’s odds and ends, and a well-positioned peg for their jacket.

It’s my bus

Having seen the prototype vehicles in build, operators who have seen the first bus are overwhelmingly impressed.

“It makes it feel like it’s my bus, like I’ve had a say in the design,” says McGill’s Buses MD Ralph Roberts. “A 5ft 5in or a 6ft 5in person is going to be equally comfortable in this cab.”

“There’s a sense of involvement in this bus that we’ve probably not had with other builds,” says Metroline Engineering Director Ian Foster.

“It’s hard for us not to be impressed and interested in what the end result is going to be for us,” says Lothian Buses CEO Ian Craig. “The real acid question is would Lothian Buses buy it? Absolutely – why not?”

“There’s definitely a feeling that we’re part of this, we’ve not just turned up and someone’s shown us a new product,” says Epsom Coaches’ Fleet Care Manager Steve Appleby.

“It will be our vehicle design, so if it doesn’t meet what the public want, then we’ve got it wrong,” says Newport Transport Engineering Director Carl Yeaman.

“I don’t know anywhere else where the customer actually gets an opportunity to have an input. I feel that I’ve contributed to the build, this is my design, so yes, it’s brilliant,” says Abellio Engineering Director Phil Pannell.

Go-Ahead Group Engineering Director Phil Margrave adds: “You certainly feel part of it. You can sit on the bus and say actually, that was something I suggested, or they’ve taken on board the discussions we’ve had.”

“It’s quite revolutionary for a manufacturer to ask its customers what they want from day one. They’ve delivered most of the product that we’ve asked for as well,” concludes Arriva UK Bus Engineering Director Ian Tarran.

Concurs Stagecoach UK Group Technical Director Adrian Havlin: “I’ve seen many first-off builds and prototypes, but nowhere near this. Not a patch on this. They have done what they said they were going to do.”

Orders and more

ADL says it will be the “most reliable and fault-free bus ever,” and has orders for over 400 in the pipeline. These include 120 that will be delivered in the next 12 months to Go-Ahead, Stagecoach, Reading Transport and other UK operators. In addition, multi-year contracts with operators such as National Express will boost this figure to beyond 400, worth a collective 80m.

Next in line is the new single-decker Enviro200, which will be launched this autumn and share many aspects with the Enviro400 MMC. The 7.5m ADL has spent on the Enviro400 project over the last two years represents a quarter of its new product development budget. There are currently 37 different projects, covering much of the current and future product range. Of this, almost a dozen relate to product development of models for the North American, Asia Pacific and Middle Eastern markets. For example, the new Enviro200 will have ‘smart’ accessories, to reduce the parasitic load on the engine from items such as hydraulic pumps and air compressors. The 18m joint ADL, Williams Hybrid Power and GKN Gyrodrive project continues, with trial vehicles expected in early 2015.

Finally, the Virtual Electric bus – a single-decker Enviro350H hybrid with greatly extended range and inductive charging announced earlier this year – has now progressed to a prototype test vehicle. The 3.5m collaborative project is ready to move to its next phase.

De-risking the business

All this is part of a clear strategy. Mr Robertson makes it clear that while ADL intends to consolidate and strengthen its position in the home market, it also remains resolute in its strategy to de-risk the business through further expansion of its global footprint – and he made his point in emphatic terms.

“We have recently won orders for nearly 600 high capacity Enviro500s – the custom-built export double-deck we launched just 18 months ago – worth around 175m, which come at a time when we are actively pursuing further initiatives to increase our build capacity in Malaysia, which is a strategic gateway to significant new territories.”

ADL’s International Business Development Director Robert Davey says that the recent Enviro500 orders include 40 for Malaysia; 70 for Citybus, 86 for New World First Bus and 171 for KMB (all Hong Kong); 201 for Singapore; and 22 for operators in Seattle, USA. In addition, ADL will also build 80 Enviro200s for operation in Malaysia.

He also announced a new-build partnership with ABC of Florida, which will assemble ADL open-top and transit double-decks at its Nappanee plant, Indiana, from the third quarter of this year.

This augments a joint venture ADL currently has with New Flyer Industries, the largest bus and coach manufacturer in North America, which is about to introduce a new midi bus to the USA
and Canada based on the Enviro200. Concludes Mr Robertson: “In total, we have now sold around 1,400 Enviro500s in export markets since its launch, which is a remarkable achievement. At the risk of sounding arrogant, I think it is fair to say that the track record and performance of our two and three-axle double decks has put us right at the forefront of this market sector, both in home and export territories.

“If we continue to support our vehicles in an unrivalled way then I see no reason why we cannot enhance our reputation and business opportunities further. Britain is now clearly a world leader in double deck bus production.”