UK low carbon buses pave the way for better air quality

Posted: 11 September 2014 | | No comments yet

The advancement of low carbon vehicles is at the heart of the UK’s climate change agenda that sets an ambitious target of reducing greenhouse gas emissions by 80% by 2050, writes Gloria Esposito – Head of Projects at the Low Carbon Vehicle Partnership (LowCVP). Low carbon buses are a key part of the UK’s roadmap to reducing CO2 emissions, an integral feature of sustainable transportation in cities and driving improvements in urban air quality. In parallel with environmental benefits, the manufacturers of low carbon buses have a role to play in stimulating economic growth through investment in the automotive industry in the UK.



Government policy has been highly instrumental in helping to kick-start the low carbon bus market via fiscal incentives that reduce the purchase and running cost of these vehicles. The leading incentive mechanism in the UK was the Green Bus Fund; running for the last four years this has provided £100 million to support the upfront cost of low carbon buses. This is particularly important as the key barrier to adopting low carbon buses, especially electric and hybrid technologies, is their much higher purchase cost compared to incumbent diesel buses. The Green Bus Fund terminated earlier in 2014 and has been superseded by a new £30 million Low Emission Bus Fund. This is part of a £500 million funding package introduced by the UK Government’s Office of Low Emission Vehicles to encourage the uptake of ultra-low emission vehicles between 2015 and 2020.

What and where?

In the UK, a low carbon bus is defined as a bus that can achieve more than 30% in greenhouse gas emission savings, measured on a well-to-wheel basis, compared to a Euro 3 diesel bus. The technologies that achieve this status are diesel hybrid, electric and biomethane (renewable natural gas). Over the past 12 months the market has seen significant development accompanied by a variety of interesting technology demonstration trials. There are currently 1820 low carbon buses operating here. A whistle stop tour of the UK low carbon bus market will hopefully provide a flavour of the country’s efforts to reduce CO2 emissions, improve air quality and help spur investment in the automotive industry.

Hybrid buses

Diesel hybrid technology occupies the lion share of the low carbon bus market, being led by UK bus manufacturer Alexander Dennis Ltd. There are 1,633 hybrid buses operating across 21 regions of the UK. Transport for London (TfL) runs the largest hybrid fleet in the UK and Europe, currently at 844 vehicles. Under TfL’s current plans, more than 1,700 hybrid buses are set to be in service in London by 2020, representing 20% of the city’s bus fleet. Improving poor air quality in London has been the driving force behind TfL’s investment in hybrid buses and plans to move towards more advanced plug-in hybrid technology.

Electric buses

Electric buses have experienced an encouraging growth rate this year. There are 64 electric buses operating in eight regions across the UK, with the British bus manufacturer Optare one of the pioneers in this market. Nottingham City Council has the largest electric bus fleet comprising of 30 buses, but this will increase to 50 by the end of 2014. The city is earmarked to have the biggest electric bus fleet in Europe. The transport authority has been forward-thinking installing both standard and fast charging electric charging infrastructure at their bus depots, using renewable energy generated from a local waste incineration plant.

York City Council has transformed a diesel city sightseeing bus into the world’s first double-decker pure electric bus. The project has been funded by a UK Government air quality initiative called Clean Vehicle Technology Fund. The electric retrofitted bus will eliminate 33 tonnes of CO2 and more than 535kg of NOx emissions per year and reduce operating costs of the vehicle by more than £20,000 per year. The vehicle has a maximum range of 90 miles, or likely to be 76 miles in real-world operation. The electric bus will not require recharging during the day but charged overnight at York’s bus depot. As part of the Council’s Low Emission Strategy, eight single-deck electric buses will also be operational by the end of 2014.

Wireless charging

The UK has been the vanguard of demonstrating innovative induction or wireless charging equipment. Milton Keynes was the first city in Europe earlier in 2014 to embark on a private and public collaboration to trial inductive charging equipment on a fully electrified route running 15 miles through the city centre. The stakeholders involved include Milton Keynes Borough Council, Wrightbus Limited, Mitsui & Co, Arup, Arriva, the University of Cambridge, Scottish and Southern Electricity, IPT-Technology, Western Power Distribution and Chargemaster Plc. The overall aim of the project is to assess the technical and commercial viability of electric bus inductive charging.

TfL plans to take inductive charging one step further by trialling this equipment with four Alexander Dennis Enviro 400H extended range diesel electric hybrid buses. The trial is part-funded through the Zero Emissions Urban Bus System (ZeEUS), coordinated by the International Association of Public Transport (UITP). The wireless charging equipment will be installed at bus stops in several locations in London to enable the plug-in hybrid buses to have a ‘top-up’ charging during their daily route. The extended period of time operating in pure electric mode will help deliver improvements in air quality and reduced CO2 emissions. The plug-in electric hybrid buses are also expected to offer much lower noise and vibration levels compared to a conventional diesel vehicle and lower fuel costs. The trial is designed to establish whether the technology can stand up to the rigors of operating in an intense urban environment such as London. Additionally, the trial aims to help TfL develop future plans for greater use of electric buses in central London, in particular contributing to the Mayor’s vision of a central London ‘Ultra Low Emission Zone’ in 2020.


2014 has seen the successful demonstration of new low carbon powertrain systems using flywheels for energy storage. One technology was originally developed by Williams for Formula One and was proven on the racetrack by Audi and Porsche. GKN Hybrid Powers has adapted this fuel efficiency technology for urban bus applications. The GKN hybrid is a kinetic energy recovery system based on a high-speed flywheel made of carbon fibers which store and releases the energy generated by a vehicle as it stops and starts. Bus operator Go-Ahead Group retrofitted GKN Hybrid Power’s ‘Gydrodrive’ flywheel technology to 20 buses in its fleet. The results of the trial were impressive. In real-world driving conditions, a 20% reduction in fuel consumption and CO2 emissions was achieved. In response to these successful trials, Go-Ahead Group has committed to retrofitting 500 buses with GKN’s flywheel technology over the next two years. This will help the company reduce their environmental footprint and fuel costs. Although flywheel systems achieve slightly lower fuel savings than conventional electric hybrid buses (circa 30%), retrofitting the technology is much less expensive than purchasing new hybrid buses. Research carried out by the Low Carbon Vehicle Partnership (LowCVP) has revealed that bus operators can achieve a payback in less than five years when retrofitting flywheel technology, without the need for grant funding.


Whilst Europe has been deploying gas buses in a number of cities for over a decade, the UK is only now beginning to expand the use of gas buses. Biomethane is presently the most widely used renewable transport fuel of bus operators. Biomethane, presently the most widely used renewable transport fuel by bus operators, is produced from organic farm and vegetable waste via anaerobic digestion, upgraded, compressed then injected into the UK gas grid. A green gas certification system enables bus operators to purchase biomethane which is then delivered via the conventional gas grid once they have installed gas infrastructure at their depot. The adoption of compressed natural gas buses powered by biomethane has grown rapidly this year, and there are now 89 vehicles operating in six regions of the UK. Reading Buses owns the largest biomethane bus fleet comprising of 34 gas buses. Reading Buses purchased the first 20 biomethane buses without the aid of external funding, relying on the benefit of lower fuel costs to cover the extra costs of the buses and investment in the infrastructure for gas supply.

Overcoming barriers

Whilst the number of low carbon buses in operating in the UK is impressive, these only represent 2% of the bus market. Research undertaken by the LowCVP has identified a number of barriers preventing the wider take-up of low carbon buses by public transport operators, including:

  • The high upfront cost of low carbon buses
  • Uncertainty in the operational performance of low carbon buses
  • Concern over battery life and replacement costs for hybrid and electric buses
  • Lack of real-world data regarding financial and environmental benefits of different technologies and fuels
  • High cost of infrastructure for electric and gas buses.

Overcoming these hurdles will involve actions from a number of different stakeholders and collaboration across industry. Government policy will continue to have a critical role to play in the near-term with regards to supporting the growth of low carbon buses. The LowCVP is actively supporting the UK Government in shaping future fiscal policy to stimulate the increased purchase of lower carbon buses. In addition the LowCVP plans to organise workshops with bus operators over the next 12 months to raise awareness about the operational performance, financial and environmental benefits of different low carbon bus technologies.

Pushing forward

The transition to a mature low carbon bus market will inevitably take time and effective partnership working between key public and private stakeholders. LowCVP will continue to bring the right stakeholders together through our Bus Working Group, and push forward influential research and policy development to expand the take-up of low emission fuels and technologies for buses and other vehicle sectors in the UK.


Gloria Esposito is an environmental scientist who holds the position of Head of Projects at the Low Carbon Vehicle Partnership (LowCVP). Her work focuses on developing the low carbon bus and passenger car market in the UK through policy research and development. Gloria has previous experience in local government at the London Borough of Camden, leading policies and initiatives to expand the uptake of clean vehicles to reduce air pollution and CO2 emissions in central London. She was responsible for establishing London’s first biomethane refueling station and integrating biomethane, hybrid and electric vehicles into local government fleets. Gloria was a Senior Air Quality Consultant at the environmental consultancy Bureau Veritas where she managed projects involving air pollution monitoring and dispersion modelling to determine the impacts of road transport and industrial process emissions on local air quality. Gloria also worked at Kings College London where she was a senior environmental consultant involved in running the London Air Quality Network.

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