Joule: The basic unit of energy; the equivalent of 1 watt of power radiated or dissipated for 1 second. Natural gas consumption is usually measured in megajoules (MJ), where 1 MJ = 1, 000,000 J. On large accounts it may be measured in gigajoules (GJ), where 1 GJ = 1 000,000,000 J.

Journey speed

It is the effective speed of a vehicle between two points, i.e. total distance / total journey time (including delays).