"fuel efficiency" . "The distance traveled per unit of fuel used; most commonly miles per gallon (mpg) or kilometers per liter (km/L).
\nNote 1: There are unfortunately no standard unit codes for miles per gallon or kilometers per liter.
\nUse unitText to indicate the unit of measurement, e.g. mpg or km/L.\nNote 2: There are two ways of indicating the fuel consumption, fuelConsumption (e.g. 8 liters per 100 km) and fuelEfficiency (e.g. 30 miles per gallon). They are reciprocal.
\nNote 3: Often, the absolute value is useful only when related to driving speed (\"at 80 km/h\") or usage pattern (\"city traffic\"). You can use valueReference to link the value for the fuel economy to another value." . . . .