All fuels work by burning. Their combustion in a vehicle engine results in rapidly expanding gases that are used to turn the engine. The motion of the engine is then transmitted to the wheels to make the car or train go or to a propellor or turbofan in the case of a plane.

Combustion of petrol mostly results in carbon dioxide and water vapour with smaller quantities of pollutants such as nitric oxide, nitrous oxides and carbon monoxide.

Different vehicles can hold different numbers of passengers. The Tyndall Centre for Climate Change Research have calculated the amount of carbon dioxide and oxides of nitrogen produced per person per mile for different modes of transport.

MODE OF TRAVEL	CO2	NOx
Air	340	0.7
Car    Petrol	298	0.95
Diesel	225	2.22
Hybrid	200	0.3
Tube / Underground	171	0.12
Rail	116	n/a
Coach / Bus	90	0.3
Car     Hydrogen	0*	0*
(Source: Tyndall Centre for Climate Change Research, 2001)

*You need to bear in mind how the hydrogen was obtained though. For more on alternative fuel choices click here.

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