Hydrogen-powered bus. This bus is powered by a fuel cell that runs on hydrogen gas. Inside the proton exchange membrane (PEM) fuel cell, hydrogen is combined with air, without combustion, to form heat and water. The electricity generated drives the bus and the only emission is water vapour. This bus is part of a European trial to test out the buses which are designed and manufactured by Daimler Chrysler. Hydrogen, which is created by the electrolysis of water, is a cheaper and more readily available fuel than oil. The buses were introduced on the RV1 route in 2004. Photographed in Borough High Street, London, UK.