Hybrid technology tested

News stories are free to read. Click here for full access to all the features, articles and archive from only £8.99.










In the years prior to full electric double-decker buses, hybrid technology was used. Richard Sharman takes a look at a used Alexander Dennis Enviro400H to see how that technology compares today

A lot can happen in a week in the coach and bus industry, which is why CBW is weekly. Imagine how much has happened in eleven years. Back in 2010 Euro V had only just been introduced, but bus manufacturers were on a drive, no pun intended, to reduce emissions even further.

Are you enjoying this feature? Why not subscribe to continue reading?

Subscribe for just £10 a month with our annual print and digital offer, Or login if you are already a subscriber

By subscribing you will benefit from:

  • Operator & Supplier Profiles
  • Face-to-Face Interviews
  • Lastest News
  • Test Drives and Reviews
  • Legal Updates
  • Route Focus
  • Industry Insider Opinions
  • Passenger Perspective
  • Vehicle Launches
  • and much more!

Battery technology is not new

Whilst we might think we are pioneering battery technology right now, the fact is that it has been experimented with in the bus industry for decades – remember the Ribble Leyland National in the late 1970s that had its own trailer filled with batteries, or the Optare MetroRiders in the early 1990s that operated the Oxford City Circuit, which needed recharging after every trip?

We know batteries and buses work well today, but a decade ago it was still very much an emerging technology and the demand was there for a new product that didn’t need to be recharged or plugged in, but could reduce fuel use and emissions whilst being a practical member of the fleet.

That vehicle was the Alexander Dennis (ADL) Enviro400H, the H of course standing for Hybrid.

Aerospace technology

The Enviro400H was born out of ADLs desire to look beyond Euro V and develop solutions for even greener bus travel. This ambition led to a partnership being formed with a company that is best know for its advances in aerospace technology, BAE Systems.

BAE Systems is, in fact, a global defence, security and aerospace company which had approximately 107,000 employees worldwide in 2010. By the time its HybriDrive had reached the UK that year, it was already well tested and utilised in North America and Europe, with 200 million miles of revenue earning service achieved. BAE claimed in 2010 that its HybriDrive had ‘provided significant environmental benefits with the prevention of the release of more than 100,000 tonnes of CO2 particulate.’

“In addition,” BAE said at the time, “the buses are helping to clean up pollution of another kind as they offer quieter operation. These benefits combine with fuel consumption reductions of up to 40% (depending on duty cycle), which so far have exceeded savings of 10 million gallons of diesel.”

That milestone had been achieved by BAE Systems working with Daimler and New Flyer in the United States and ADL and Irisbus Iveco in Europe.

ADL’s involvement in the roll-out in Europe included the Enviro350H single-decker chassis, which was offered with Tata Hispano bodies, and would later arrive in the UK as the Enviro350H with Stagecoach taking a number of examples in Aberdeen and Perth, whilst First Bus also operated them in Essex. An Enviro400H was also introduced for the European open-top bus tour market with a Unvi Urbis body.

The Enviro400H has a welcoming appearance. RICHARD SHARMAN


Enviro400H roll out

2010 was the year that ADL capitalised on BAE Systems’ HybriDrive technology, following a successful roll out in Europe. Offering a potential fuel saving of 40%, the Enviro400H was an attractive option for operators looking to ‘greenify’ their fleets. By the end of 2010 over 100 vehicles had entered service in London and Oxford, with Edinburgh and Reading following suit. The model continued to be a success with Transport for London contractors, and many more examples were delivered.

Stagecoach Group also took delivery of 258 Enviro400Hs for operation in Oxford, the North East, Yorkshire and Manchester between 2010 and 2013. Since the first incarnation of the Enviro400H, ADL has sold more than 1,400 vehicles.

Current offering

The Enviro400H forms part of the current Major Model Change (MMC) range, with operators also having the option to specify the City body. Additionally, ADL has gone on to work with BAE Systems on the Enviro400ER which offers geofenced zero-emission capability, giving it the ability to reduce pollution hotspots in towns and cities.

The Enviro400ER uses BAE Systems’ series hybrid technology, as used in the Enviro400H, but it can run for up to three miles in electric mode, with the exact distance depending on factors such as travel time and route profile. The vehicle utilises a 32kWh capacity energy storage system, comprising third generation lithium nickel manganese cobalt battery technology, which has the benefit of not needing to be charged externally, thus reducing the cost of depot infrastructure.


A single seat is situated behind the cab. The vehicle’s electronics are located behind the panel next to it. RICHARD SHARMAN












Second hand market

Many of the Enviro400Hs are still with their original owners. In fact some of the first examples to be delivered in 2010/11 were to the Oxford Bus Company and Stagecoach in Oxfordshire, which are still running these vehicles alongside newer Euro VI Enviro400MMCs today.
Reading Buses, which operates a total of 35 Enviro400Hs has experimented with various re-powering options for these vehicles later in their life. Options trialled include a plug-in-electric drivetrain with a CBG engine, in partnership with Magtec, installing a Vantage Power series-hybrid system with stop-start and zero-emission running capability, which was not completed, before trying a conversion to standard diesel operation by fitting a gearbox. A number of these vehicles are now fully converted to diesel.

However, operators now have the opportunity to purchase these fuel-saving vehicles as they come out of service with Transport for London contractors. The Bus & Coach Centre in Oxford currently has four examples dating from 2012 available for sale. I took the opportunity to test drive one of these vehicles to find out how it had fared after nine years services in the city of London.

Measures have been taken to reduce seat fabric wear on the lower deck rear facing seats from shoe damage. RICHARD SHARMAN


Returning off lease

The four examples at the Bus & Coach Centre have had an interesting history, being some of the very last vehicles delivered brand new to First London before it sold its operations in June 2013 to Go-Ahead London, Metroline and Tower Transit.

The vehicle tested, SN12 ASO, was new to First as DNH39118 and operated on Transport for London (TfL) service 23 between Liverpool Street station and Westbourne Park. This route and batch of vehicles moved to Australian-owned Tower Transit with the sale of First London, and this batch of vehicles would spend its whole life on this one route. Service 23 is now operated by new zero-emission Switch Mobility MetroCitys. Some of the same batch of Enviro400Hs have been retained and have just been refurbished by ADL’s Harlow workshop for continued work on the TfL network.

A large wheelchair bay is fitted, with wheelchair access at the centre of the vehicle through the Ventura sliding doors. RICHARD SHARMAN












An air chiller unit is fitted above the staircase. RICHARD SHARMAN












First impressions

Arriving at the Bus & Coach Centre I was greeted by Danny and Will, who had prepared the vehicle for the test drive.

As can be expected from a vehicle that had been operating on a TfL contract, the interior of SN12 ASO was in excellent condition for its age, having been recently re-retrimmed by Tower Transit, by the look of it. The bus still showed signs of its original FirstGroup ownership, with various parts of internal trim and handrails to First’s corporate specification, and which all still looked in good order.

In dual-door configuration the Enviro400H can seat 61 passengers with 24 standing and one wheelchair passenger. The bonus of it being used on TfL work is that it also adds an air chiller unit on the upper deck above the staircase.

The driver’s environment of the Enviro400H is also a pleasant place to be. Even with the fixed assault screen in place, there is still plenty of room. The instrument binnacle is the same as a standard Enviro400, although the driver benefits from auto interior lights, auto headlights, cab air-conditioning, reversing sensors, and a comfortable Chapman drivers seat with three-point seatbelt, plus audible warnings for when the cab door is open with the handbrake off, when reverse is selected, if the engine fire suppression system is active and so on. This can be heard on the YouTube video that accompanies this feature, released on our YouTube channel on Thursday 5 August.

The driver has a good sized working environment. RICHARD SHARMAN












A CCTV monitor is fitted in the cab, and in the lower saloon. RICHARD SHARMAN













Out on the road

Oxford is the home to a large number of Enviro400Hs, so it was only right to take this example for a trip around the city centre and a blast around the ring road.

This was to be my first time driving the hybrid variant, and I was looking forward to seeing how it compared to the standard version. It was quite a warm day for the test drive, and on starting the engine the vehicle’s interior sensors activated the saloon fans to cool the vehicle.

Departing from the depot I was quite surprised by how responsive the throttle was. Not only that, but this was not the normal chatter you would expect to hear from a Cummins engine. The smaller 4.5-litre four-cylinder 185bhp unit can be heard in the background, but it is not actually the engine that is doing the work. Its sole purpose is to power the generator and the vehicle’s air compressors. The BAE HybriDrive system uses a compact 200kW electric traction motor, which takes its power from the generator, and provides high torque in the form of acceleration from the vehicle’s bank of lithium-iron batteries. Regeneration occurs upon braking.

Pulling onto the A40 it was foot flat down to keep up with the traffic. However, one aspect of this vehicle is that its top speed is not as good as one with a big Cummins lump, but as there is no gearbox to go through, the acceleration is fairly rapid. On the flat it is good for for a respectible 45-48mph, which if you know your ex-London buses, is much better than a three-speed MCW Metrobus back in the day where you would be lucky to achieve 38 to 42mph!

Heading towards Oxford city centre on the A40 I was listening out for any rattles or bangs from the interior trim. However, for its age and some 450,500km, I could barely hear any, which I was impressed with having driven various newer vehicles that do have rattles.

In the city

On the flat the Enviro400H is OK, but this bus is designed to be in the city, so that is exactly where I headed.

This example is short at 10.2m, but tall at 4.4m (14’6”). I wondered how this translates to the vehicles handling. Sitting on Bridgestone 275/70R 22.5 tyres (and still with the original Dennis wheel trims!), the handling at speed had so far been fine. Navigating the city streets the Enviro400H felt quite nimble, with light steering that gives you some feedback from the road surface, which is nice when compared to some new vehicles that offer none.

By this time I had been on the road for a good 40 minutes and it was time to see if the air chiller unit had cooled the upper deck. Sure enough it had dramatically reduced the saloon temperature. I also had the cab air-conditioning on and this was working well. Whilst checking the saloon I found that the multiple camera CCTV system was in full operation and scrolling through the cameras on a TFT screen mounted behind the staircase.

Whilst navigating the city I found that the assault screen caused no issues with reflection in the mirrors and that all-round vision was very good.

These vehicle are dual-doored, but the Ventura twin sliding doors are quick in operation and are beneficial on both service and school work. An electrically-operated wheelchair ramp is also fitted to the rear doors.

An hour into the drive I felt that I was really enjoying the smoothness of the drive, in terms of suspension, acceleration and the brakes.

The example tested was 10.2m long and 4.4m (14’6”) high. RICHARD SHARMAN












The Cummins engine sits to the left of the engine bay, and the HybriDrive system to the right. RICHARD SHARMAN












In conclusion

For vehicles that are now nearly 10 years old, I was impressed with the condition of them and how this particular example drove. The cab is a nice place to be and the passengers benefit from a spacious interior with plenty of legroom and interior sensors that can respond to high heat or cold conditions.

For technology that was developed a decade ago, its still impressive today, and that is a credit to both ADL and BAE Systems.

Four of these vehicles are currently available from the Bus & Coach Centre: call Will on 01865 570775 for
further details.