Lane meter

University of North Carolina's How Many? A Dictionary of Units of Measurement, defines a lane meter as:

A unit of deck area for "roll on/roll off" ships: cargo vessels designed so that containers or other cargo can be rolled on and off the decks of the ship. A lane is a strip of deck 2 metres wide. A lane metre is an area of deck one lane wide and one metre long, that is, 2 square metres (21.528 sq ft).

The rule of thumb is that a car on a car ferry will need 6 meters, and a semitrailer with a European truck 18 meters.