London bus using electric hybrid technology

The big red bus goes hybrid-electric

London's iconic red buses are going green, as the city - like many others around the world - strives to cut pollution and save fuel.

London's bus network is one of the biggest urban transport systems in the world. It comprises roughly 8,500 individual vehicles run by nine different operating companies awarded contracts to provide services by the city's overall transport authority, Transport for London (TfL). In any 24-hour period, some 6.4 million passenger journeys take place over approximately 700 different routes.

At present almost all those buses are solely powered by diesel engines. The exceptions are 56 buses running over ten routes, mainly in the central area of the city, using hybrid propulsion systems in which diesel engines are supplemented by a combination of electric motor, battery and generator. These vehicles have been gradually joining London's bus fleet since 2006, but despite their small number they emphatically represent the future of road-based public transport in the city. That is because from the Olympic year of 2012, it is TfL's intention that all new buses that appear on the capital's roads will be hybrids, and that ultimately the whole network will comprise only hybrids.

The reasons for the policy are pretty straightforward, says Mike Weston, operations director for London Buses - the division of TfL responsible for London's bus services. He explains that diesel engines produce three major types of emission: particulates, oxides of nitrogen (NOx), and carbon dioxide. The first two are limited by European legislation that targets engines in isolation rather than in service, but he says that in the case of particulates TfL has imposed much more stringent requirements for emissions reductions on its service providers.

All bus types that operators want to introduce to the capital's roads must therefore undergo testing at Millbrook Proving Ground in Bedfordshire. This simulates an existing service within the city - Route 159, which at the time it was selected ran from Brixton, south of the River Thames, right through the city centre to Baker Street, although it has subsequently been extended slightly. Only buses that demonstrate that they can meet TfL's requirements over the course of this virtual journey are approved for use.

In the case of CO2 emissions, a number of factors have coalesced. Weston cites both TfL's commitment to providing environmentally efficient transport services, and the Mayor of London's Air Quality Strategy, against the general background of concern about global warming.

The figures indicate that there is room for improvement. London's buses annually produce 610,000t of CO2 and consume 240 million litres of diesel. The correlation between CO2 and diesel is direct, and any reduction in fuel consumption will produce a corresponding CO2 reduction. Hence the introduction of hybrid buses, with an official target of a 30 per cent reduction in CO2.

So far the use of hybrid buses on London's roads has been experimental and, as Weston explains, the project has been deliberately structured to maximise the generation of broad-based, useful experience and knowledge. For a start, four different bus builders have been used - Swedish company Volvo, and three UK outfits Optare, Alexander Dennis and Wrightbus. Similarly, there is both a mix of propulsion system types and suppliers, including BAE Systems and Siemens.

Hybrids fall into two main categories - series and parallel. In the first, there is no connection between the diesel engine and the vehicle's wheels. Instead the diesel engine, which can be smaller than in a pure diesel vehicle, runs at a near constant speed to power a generator. This charges a battery, which powers an electric motor driving the wheels.

In a parallel format, the diesel engine can also drive the wheels directly if necessary. A third 'blended' option allows both diesel and electric power to be used simultaneously. But whatever system is used, a 'stop-start' capability by which the diesel engine is automatically switched off if the vehicle is stationary - most obviously at a bus stop - can also be included.

All these options have been tried in London, and Weston says that while other cities in the world may be more advanced in their use of hybrids - New York, for instance, has around 1,000 such vehicles - London has led the way as a large-scale test location for multiple technologies. He says that by focusing on a relatively small number of routes (which do not include the emblematic Route 159) it has been possible to assign half a dozen or so hybrid buses to each and ensure their sustained use. As he dryly notes, if the vehicles had been more widely scattered then in the event of a breakdown a local manager might have been able to substitute it with a diesel counterpart. But the approach adopted by TfL has made the hybrids integral to the operation of the routes involved.


Weston is also emphatic that experience has shown that much more widespread adoption of hybrid buses in London - indeed, the complete hybridisation of the city's bus fleet - is entirely feasible. Not only has the targeted reduction in fuel consumption been achieved, but feedback from passengers has indicated that they have noticed and appreciate that the hybrid buses, which are easily recognisable through their use of a 'green leaf' livery, are less noisy and provide a smoother ride than diesel vehicles. Weston says that the hybrid vehicles generate around 68-69db of noise, 5db less than diesel counterparts. From the bus operators' point of view, hybrids do not require any supplementary infrastructure, though drivers may require some extra training.

In fact, the only real impediment to the rapid expansion in the use of hybrid buses is their cost. Weston says that a hybrid double-decker typically costs around 50 per cent more than an equivalent diesel vehicle - £300,000 as against £200,000. In the case of the London experiment, the roughly £5m involved in the provision of the first 50 hybrid buses was met from the national government's Green Bus Fund, an initiative specifically intended to help defray the extra costs involved in introduced new environmentally-friendly vehicles in UK public transport networks. But he is confident that as the numbers of hybrid buses ordered and built increase, economies of scale will kick in.

London will certainly be doing its bit. Later this year the first five hybrids to use hydrogen fuel cells instead of diesel engines will be introduced. Weston says that their hybrid nature should significantly improve on the limitations of range and endurance that affected previous pure fuel cell vehicles trialled in London.

Symbol of London

By the beginning of 2012, there should be 300 hybrid buses in London. After that the drive will be on to make the whole of the city's bus fleet hybrid. Weston says that around 800 buses are retired from service and replaced each year, and at that rate the transformation would be complete by around 2024.

The hybrids will, of course, include a new generation of the iconic, open-backed Routemaster buses that were an unofficial symbol of London. Tradition and technology, in other words, will be combined to ensure that millions of people will be able to travel around one of the world's major cities in a way that is efficient for them and the wider environment.

FAs the use of hybrid buses in London demonstrates, some of the biggest names in engineering, not just the automotive sector, are involved in the production of hybrid propulsion systems, and as in all other sectors each player has a distinctive background, technological approach and marketing strategy. Perhaps the most unexpected name is that of the predominantly aerospace-related defence industry giant BAE Systems. The company's operations in the field - its manufacturing and most of its R&D - are based in New York, US and derive from an acquisition made 15 years ago. But it also has a smaller UK site in Rochester, Kent, where activities in Europe are coordinated.


Business development director Ian Wilson says that it does not make every element of its hybrid propulsion systems itself - the batteries, for example, are bought in. But he emphasises that BAE provides its own control system, derived from its expertise in aerospace engines. He says that BAE regards its ability to exploit its own aerospace expertise in the development of hybrid systems for terrestrial propulsion as one of its particular strengths.

Wilson confirms that the company is firmly committed to the series rather than the parallel concept. 'We believe it is the best approach for buses that operate at low speed and in a constant stop-start mode,' he explains. The concept, he adds, is not intrinsically superior to its parallel counterpart, but provides the optimal solution in the circumstances. 'It is purely down to the duty cycle of the vehicle,' he notes.

Around 2,700 buses use BAE's propulsion technology, most of them in North America. The first 1,500 or so used lead-acid batteries, but more recent models use much more efficient lithium-ion - a technology that BAE introduced four years ago. The new batteries provide the same storage capacity in half the weight, and Wilson says their introduction marked a step change in the capabilities of the systems the company can offer. It means that in a typical double-deck bus the total weight of the batteries would now be 365kg.

A hybrid future

Wilson suggests that the next step in the development of hybrid technology - one that BAE is investigating - might be to replace the diesel engine and generator combination with fuel cells. That would dovetail neatly with the introduction of all-electric buses - vehicles in which subsidiary systems, which are currently electro-mechanical, for instance doors operated by pulley belts, would instead have localised electric motors - another development that Wilson expects to see in the near future. BAE itself, he adds, is also likely to start some relevant manufacturing operations in the UK as the European market for hybrid technology begins to take off.

Meanwhile, another supplier of hybrid propulsion systems is already manufacturing in Europe, namely Siemens. Mick Jones, business manager for large drives, says all the company's relevant manufacturing and R&D activities are based in Nuremberg - although Jones himself is based in Manchester, where UK marketing and sales operations are overseen. The location is appropriate because the city has ordered 66 hybrid buses using Siemens technology from Optare, with the first 20 due in service this autumn.

Interestingly, Jones says that Siemens does not regard itself as a supplier of complete hybrid packages, but rather as a facilitator that can help bus builders configure their own systems. But the main point he makes is simply that for a company with the depth of application experience that Siemens possesses, hybrid propulsion technology is in no way 'futuristic'.

In short, as the experience of London shows, hybrid propulsion for public transport is real, reliable and likely to be increasingly affordable. If the will is there, there are no real barriers to its widespread adoption - with all the benefits it brings in its wake.

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