A quiet revolution is slowly unfolding in Britain's city centres as zero-emission electric buses start helping to reduce urban air pollution and background noise levels. Already a supporter of battery power as a means of making mass transit cleaner and more efficient, Nottingham City Council, for example, is taking delivery of 13 single-decker electric 12m ebuses, constructed by Chinese manufacturer BYD, towards the end of this year. They will join 45 electric buses already operating there. Two 12m BYD ebuses are also in service in central London with Go-Ahead.
Nottingham's new acquisitions have a claimed range of just over 155 miles, so seem unlikely to run out of juice between stops. However, costing around one-third more than their diesel equivalents – BYD can arrange for the batteries to be leased to reduce the upfront premium – ebuses do not come cheap. In Nottingham's case, their purchase was part-funded by a £1.4m grant from the DfT's (Department for Transport) Green Bus Fund. The £2.1m balance comes from the city's workplace parking levy.
Recharge times? Go-Ahead's ebuses have to be plugged in for five hours, but can then tackle a 17-hour shift, says BYD. Charging technology is continuing to develop it adds, with two hours now a realistic figure. Also, BYD unveiled a 47-seater electric coach with a claimed range upwards of 190 miles earlier this year, although as yet there are no plans to market it in the UK.
But BYD is by no means the only electric bus manufacturer. Rivals include Optare and Wrightbus. Last year saw eight electric Wrightbus StreetLite 9.6m single-deckers go into service with Arriva on a 15-mile route through the centre of Milton Keynes. In this case, an induction charging point was installed in the road at both ends of the route, and now a 10-minute layover replaces two-thirds of the energy consumed during each 15-mile run.
One issue: traction batteries eventually have to be disposed of, which raises environmental concerns. However, BYD contends that the iron-phosphate batteries it installs still hold 75% of their charge after 10 years of service and can thereafter be switched to static applications.
Also equipped with batteries, diesel-electric hybrid buses can also make use of an induction charging systems. Last autumn's Euro Bus Expo, held at Birmingham's NEC, saw Volvo and Lothian Buses extolling the virtues of a system that employs roof-mounted rails rather than a plate in the road. This allows the Volvo 7900H 12m hybrid single-deckers Lothian operates to run for almost five miles on battery power alone.
Meanwhile, battery disposal is not an issue with some other packages becoming available. Last November, ADL committed to acquiring 250 Gyrodrive electric flywheel systems from GKN Hybrid Power. Designed to last for the life of the vehicle, Gyrodrive employs a high-speed carbon fibre flywheel to store energy generated by a bus as it slows down. That energy is then used to power a GKN EVO electric motor, which helps accelerate the vehicle back up to speed.
One Euro 6 Enviro400 double-decker fitted with Gyrodrive has already achieved Low Carbon Emission Bus Certification, says ADL. This acknowledges a 30% cut in CO2 emissions, which gives an indication of the fuel saving and entitles operators to enhanced fuel rebates.
Heading down a similar path is Wrightbus with the Flybrid KERS (kinetic energy recovery system) developed in a collaborative project with Torotrak, Voith Turbo, Productiv and Arriva. This received a £698,000 award from Innovate (formerly the Technology Strategy Board) and is now being trialled in a StreetLite operated by Arriva in Gillingham, Kent.
This too uses a fast-spinning flywheel to capture energy but in this case the flywheel is linked directly to the rear diff by its own prop shaft, transferring energy as the bus pulls away. "It saves enough fuel to pay for itself in less than five years," comments Torotrak commercial director Jon Hilton.
However, this should not be confused with the Micro Hybrid package offered on both StreetLite and the new StreetDeck double-decker. This also recovers and stores braking energy, but then uses it to power the bus's pneumatic, hydraulic and electrical systems.
What about gas? Most believe gaseous fuels have a significant role to play. Biomethane produced by a local sewage treatment works, for example, is being used to fuel one bus operated by Bath Bus Company on a shuttle service between Bristol Airport and Bath city centre. The new vehicle produces up to 30% less CO2 than equivalent diesel buses. Then, at the other end of the UK, Aberdeen saw the opening of a hydrogen production and bus refuelling station this year that will be used to fuel 10 fuel cell buses built by Van Hool. Six will be operated by Stagecoach while four will join First.
Government funding for the purchase of low-emission buses – and the infrastructure to support them – has been given a fresh boost with the launch of a £30m package by OLEV (the Office for Low Emission Vehicles). It will be available from April 2016 to March 2019.
All that said, one of the best ways of reducing fuel usage – and hence emissions – is to cut the vehicle's weight. ADL has slimmed both the Enviro400 and the single-decker Enviro200 which means the latest Euro 6 versions are lighter than their predecessors to the tune of 400kg and 200kg respectively. Meanwhile, Optare's MetroDecker double-decker (unveiled in 2014) boasts an unladen weight of just under 10 tonnes, thanks to its integral construction and the use of composite panels. Powered by a 5.1-litre twin-turbo Mercedes-Benz diesel, this unit highlights another trend – the drift to smaller, lighter engines at Euro 6. And an all-electric model is set to break cover later this year.
So which way is the wind blowing? "Electric buses represent the future," suggests Optare chief executive officer Enrico Vassallo. "I do not see hybrid technology as a long-term solution."
Top gear
Fuel economy on gas and diesel engines is heavily influenced by gearbox programming and, specifically, the timing of gear changes. In Allison's case, its new FuelSense package – which is suitable for use on its automatic bus transmissions – is said to be capable of improving economy by up to 20% compared with the its earlier generation transmissions.
It does so by taking into account factors such as how steep an incline is and how heavily the vehicle is laden and optimises the shift pattern accordingly.It draws the data it needs from sensors attached to the engine and transmission and from a built-in inclinometer.
Braking systems
While fuel economy and environmental impact are key considerations, safety is of paramount importance, particularly on passenger vehicles. AEBS (advanced emergency braking systems) have been mandatory for all new type approvals granted for coaches since 1 November 2013 – although not on slower-moving buses. Stage 1 AEBS will be compulsory on all newly-registered coaches from 1 November this year, while Stage II, which imposes more demanding deceleration, will be introduced on 1 November 2018.
Both stages mandate equipment that can detect moving, decelerating and stationary vehicles ahead and alert the driver. If there is no response, then the matter is taken out of his or her hands; and emergency brakes are applied automatically.