Diesel/Electric Hybrid

A hybrid bus combines two power sources in the vehicle drive train - a conventional diesel engine and an electric motor. The hybrid system enables energy to be recovered during braking and then released to accelerate the vehicle. There are several different types of hybrid architectures; such as series, parallel, flywheel and micro-hybrid. These powertrain systems can be used with various types of energy storage, (using chemical batteries or mechanical flywheels for example).

Diesel hybrids are the most common form of low emission bus technology in the UK to date.

Bus manufacturers of hybrids include:

Wrightsgroup logo

“Our hybrid-electric and Micro Hybrid buses offer the best fuel consumption and operating costs in the market. We partner with world-class suppliers and select the best for every bus.”


Alexander Dennis logo

“Alexander Dennis Limited (ADL) is the UK’s leading bus and coach manufacturer, employing around 2,000 people at facilities in the UK, continental Asia and North America.”


Volvo logo

“With our 7900 Hybrid range of city buses, we offer an enhancement to any existing fleet. Better performance, both on the road and on the bottom line, adds value to public transport services. You’ll simply get more kilometres for your fuel money, and a head start in reaching your environmental goals.”


Optare logo

“Our fully electric vehicle range is leading the way in zero emissions technology, while our Euro 6 Diesel and hybrid options still offer operators the full range of power options depending on their requirements.”



Case Study

National Express in Birmingham

National Express Bus logo


National Express UK Bus operate a fleet of 1,624 buses nationally, with an average fleet age of just under nine years, spread across ten depots in Birmingham, the Black Country and Coventry.

The Green Bus Fund assisted the procuremnet of 48 hybrid buses, 18 of which, (Volvo B5LH) were deployed in Birmingham.


The hybrids showed a 8.65mpg (a 30% improvement over a reference diesel bus) when new. Five years later, this has dropped to 8.57mpg, with the batteries showing no significant signs of degredation.

Challenges that arose:
  • Training Maintenance Staff
  • Training Drivers to use the regenerative braking correctly
  • Training local fire department (different emergency attendence criteria)
  • Risk to pedestrians not paying attention to quieter vehicles
  • Restrictive operating environment
  • Total cost of ownership (especially high if it had not been subsidised by Green Energy Fund)
Other Points to Note - Marketing:

A better enviroment - inside and out flyer cover

National Express produced flyer that were distributed to customers on the routes the new buses operated on, highlighting the greener credentials of the new buses, withtheir smoother, quieter ride. They also provided money off vouchers to try an encourage more patrionage on the new hybrids.

Next Steps:

Despite the challenges, National Express plan to continue to work in partnership with Birmingham city council in an Advanced Quality Partnership Scheme to reduce the cities emissions. This includes owning and operating more hybrids as well as adding other bus technologies to their fleet mix (mainly electric and Hydrogen, as part of Birmingham city council's Hydrogen Bus Project.)

A full presentation of this case study was given by Darren Astbury, Head of Engineering Development at the LEB Workshop in Nottingham, Nov 2017

Download presentation

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