There are 3,854 hybrid buses, 785 battery electric buses, and 22 hydrogen fuel cell buses operating in London, as of March 2022, out of a total bus fleet of 8,795 - this is around 53% of the bus fleet. The battery electric fleet of the city (about 9% of the total fleet) is the second-largest in Europe, after Moscow, which has over 1000 electric buses operating. From 2021, all new buses will be zero emission, and the entire bus fleet will be zero emission by 2034, although Transport for London have stated that with additional funding, this could be achieved by 2030. In 2021, it was announced that all buses in the fleet meet or exceed Euro VI emission standards, following the phasing out of older buses, the retrofitting of diesel vehicles and the introduction of new hybrid & electric buses. Background In 2006, transport was responsible for around 20% of London's CO2 emissions; with buses making up 5% of the transport total. The city 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. Diesel buses also produce particulate pollution, which is harmful to health. By using less diesel fuel, operators can also reduce the running cost of their bus fleet. 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. Battery electric buses use on-board batteries to power an electric motor that drives the bus. Unlike a hybrid electric bus, there are no local emissions. As with hybrid buses, regenerative braking is used to charge the batteries. Hydrogen fuel cell buses use the reaction of hydrogen with oxygen to generate electricity that drives the bus with an electric motor. The only emission from the bus is water. Operational history In the 1990s, early efforts to improve emissions involved replacing older diesel buses such as the AEC Routemaster, use of Ultra-low-sulfur diesel, and fitting particulate filters to exhausts. In 2000, three DAF SB220 East Lancs Myllennium buses powered by liquefied petroleum gas were used to transport visitors to the Millennium Dome. By December 2005, all buses met Euro II emission standards, with the