Hydrogen and LPG fuel road markings, directing vehicles towards the pumps for these fuels. In hydrogen-powered vehicles, hydrogen (from the fuel tank) and oxygen (from the air) react to form water and electrical power. The only by-products are heat and water, making this technology a clean source of power compared to the pollutant gases and carbon dioxide produced by the burning of fossil fuels. Vehicle engines that run on liquefied petroleum gas (LPG) produce less carbon dioxide and pollutant emissions than cars running on diesel or petrol. Photographed in June 2018, at Beaconsfield services on the M40, near Beaconsfield, Buckinghamshire, UK.