HYPASSE is a project to study and test how surpluses of electricity can be utilised to power busses. The surplus electricity is used for the electrolytic production of non-fossil hydrogen, which becomes a fuel for city busses. The hydrogen is stored in the bus in pressure tanks at 300 bar. These tanks are placed on the roof of the bus. The bus is powered by a hydrogen engine with internal mixture formation which is based on a standard-production diesel engine. With the same energy consumption as for a conventional engine, the exhaust gas emissions of that engine are about 10 % nitrogen oxide and less than 1% carbon monoxide and hydrocarbons of the limits valid as of 1996 in the EC.