first Euro IV bus entering service in April 2006. Early trials and tests In January 2004, three hydrogen fuel cell powered buses were introduced on route 25 on a two-year trial. These were transferred to route RV1 in September 2004, and were tested in commercial service on the route at peak times only. They were withdrawn in January 2007. 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. The single decker buses were unveiled by Mayor of London, Ken Livingstone on 7 February 2006, with the intention of starting operation on the following day. Later in 2006 the vehicles were temporarily withdrawn from service when their diesel engines overheated. 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. It entered service in February 2007 on route 141. An ethanol fuelled double-decker bus was operated by Transdev London in 2008 and 2009. In 2010, eight hydrogen buses were introduced on route RV1, with a substantially larger range than the fuel cell buses used in the mid 2000s. At the time, this was the largest hydrogen bus fleet in Europe. Introduction of hybrids Twenty-five vehicles entered service in December 2008, introduced onto five routes run by four different operators. A further eighteen entered service in July 2009, when six Volvo B5L double-deckers joined the existing vehicles on route 141. 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. It was originally intended that every bus introduced into service after 2012 would be a hybrid, but this requirement was later dropped. 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. Retrofitting diesel buses In the