Low emission buses in London

Hybrid electric buses use a combination of an electric battery pack and a diesel engine to provide power, and produce around 40% less carbon dioxide (CO₂) emissions than traditional diesel engined buses. Energy generated during braking is used to charge the batteries of hybrid vehicles.[3]

Transport is responsible for around 20% of London's CO₂ emissions; buses make up 5% of the transport total. The city has set a target of a 20% reduction in emissions by the year 2020. Converting London's entire bus fleet to hybrid vehicles would reduce CO₂ emissions by around 200,000 tonnes per year.[4]

Other low-emission buses have also been used in London. Three hydrogen fuel cell powered buses were used on route 25 from 2004, but have since been withdrawn; eight were operating on route RV1, but those buses have gone to route 444 ever since RV1 got withdrawn. An ethanol fuelled double-decker bus was operated by Transdev London in 2008 and 2009.[5]

Route 141 was the first in the world to be operated with a hybrid double-decker. Although the original vehicle has left the route, it is still served by hybrids such as this Wright Gemini 2 integral.

The first hybrid buses to enter service in London were six Wright Electrocity single-deckers. These were ordered in March 2005 to operate on route 360.[6] The buses were unveiled by Mayor of London, Ken Livingstone, on 7 February 2006, with the intention of starting operation on the following day.[7] Later in 2006 the vehicles were temporarily withdrawn from service when their diesel engines overheated.[4]

A double-deck hybrid vehicle intended for use in London was unveiled in October 2006. The bus, which cost £285,000 and was constructed by Wrightbus, was the first hybrid double-decker in the world, and was painted in red and green to symbolise the environmental benefits.[8] It entered service in February 2007 on route 141.[3]

No more hybrids were delivered until December 2008, when twenty-five vehicles entered service. These were introduced onto five routes run by four different operators. A further eighteen were due to follow in January 2009.[9] However, the last of these did not enter service until July, when six Volvo B5L double-deckers joined the existing vehicles on route 141.[10]

Transport for London stated that it intended to have introduced around 300 hybrids into service by 2012. This was achieved in July 2012, when an Alexander Dennis Enviro400 double-decker of Abellio London became the 300th hybrid in use when it entered service on route 211.[11][12] It was originally intended that every bus introduced into service after 2012 would be a hybrid,[4] but this requirement was later dropped.[13]

The New Routemaster double-decker was specified and constructed to a hybrid design. The first eight vehicles entered service with Arriva London on route 38 in February 2012.[14] By 2016, 1,000 New Routemasters will be in use. However, the buses have suffered from problems with their battery systems with some operating solely as diesel vehicles, and in total 200 buses will have power units replaced under warranty.[15]

A Kinetic energy recovery system using a carbon fibre flywheel, originally developed for the Williams Formula One racing team, has been modified for retrofitting to existing double-decker buses. 500 buses from the Go-Ahead Group will be fitted with this technology from 2014-2016, anticipated to improve fuel efficiency by approximately 20%.[16] The team who developed the technology were awarded the Dewar Trophy of the Royal Automobile Club in 2015.[17]

There are 3,669 hybrid buses, 155 electric buses, and ten hydrogen buses operating in London, as of March 2019, out of a total bus fleet of 9,142.[1] This includes a trial of the world's first electric double decker bus, which started in October 2015.[18]

A variety of models of hybrid vehicle are currently used. These include Alexander Dennis Enviro200H, Wright Electrocity, Optare Tempo and BYD electric bus single-deckers and Volvo B5LH, Wright Gemini 2, Alexander Dennis Enviro400H, New Routemaster and Wright SRM double-deckers.

By 2020, Transport for London has committed to the use of electric or hydrogen buses for all 300 single decker buses in Central London, and the use of hybrid buses for all 3,000 double decker buses in the same area.[2] This is part of the Ultra Low Emissions Zone scheme. By Autumn 2016 all-electric IrIzar i2e buses, with planned end-of-life battery management, will be introduced on routes 507 and 521 in central London. These vehicles will operate for fourteen to sixteen hours—six hours drive time in typical traffic conditions—between overnight charges of six hours (excluding the sixteen-hour initial charge to bring the sonick molten salt battery batteries up to their operating temperature of 270˚C).[19] All vehicles on these two routes will then be electrically powered.[20][2]

A trial of inductive charging technology for three modified Alexander Dennis Enviro400H double-deckers was announced in August 2014. The vehicles, on route 69, receive current to charge the traction batteries while at stands at either end of the route. Although it is intended that the units are to operate in "pure electric" mode, a standard diesel engine is also carried.[21]

The introduction of hybrid vehicles in London has received praise from the Low Carbon Vehicle Partnership, which awarded Transport for London the first ever Low Carbon Champion Award for Buses in July 2010.[22]