Natural gas is a clean fuel in comparison with gasoline and diesel. Its lower carbon content means that it produces about 20 per cent less carbon dioxide emissions than traditional fuels. It produces only negligeable quantities of fine particles and toxic gases.

Buses and lorries were the first to use natural gas as a fuel in Switzerland; private vehicles are now also available. Most run additionally on petrol (gasoline): the driver can switch from one fuel to the other.

The network of natural gas filling stations is being constantly enlarged, but there are still some gaps.

Scientists at the Federal Institute of Technology in Zurich, together with colleagues from the private sector in Germany, have been working on the Clean Engine Vehicle Project to optimise natural gas engines.

Natural gas is used chiefly in the home, for heating and cooking. The filling stations take their supplies from the gas network.

Natural gas is not a renewable energy source.

Liquefied petroleum gas

Liquefied petroleum gas (LPG) is not common in Switzerland, and LPG vehicles are not sold on the Swiss market. There are very few LPG filling stations.

This contrasts with many European countries, where LPG vehicles are the third most popular type after petrol and diesel.

Although this fuel - a mixture of propane and butane - produces fewer pollutants than conventional fuels, its CO2 emissions are more or less the same.

LPG and natural gas are not interchangeable: an LPG tank could not withstand the pressure at which natural gas is carried.