Hydrogen fuel cell bus, London, England. Water vapour is seen venting from an exhaust pipe (upper left). The water vapour forms from the reaction between hydrogen and oxygen in the fuel cell to produce electrical power. This is a cleaner source of power compared to the burning of fossil fuels to form carbon dioxide and other pollutant gases. The bus is part of the CUTE (Clean Urban Transport Europe) project, a demonstration project that is testing 27 hydrogen fuel cell buses, three each in nine European cities. The project started in 2002. London's three buses arrived in November 2003, and began operating in January 2004. The buses are Mercedes-Benz Citaro hydrogen fuel cell buses made by Daimler Chrysler, and are being used on route RV1. Photographed in September 2005.