There was a study done in Portland, Oregon to find the average length of a car. They wanted to see what size parking spaces would be needed to accommodate people.
They measured 390 vehicles (Front bumper of the body to the rear bumper) and found the average length of 13.51706036745407 feet (4.12 meters). This is the average size for midsized sedans/coupes (combustion engines).
A vehicle over 16.40419947506562 (5.0 meters) would be considered a large sized truck or SUV (Usually Commercial sized heavy duty diesels, like the Ford F-350-450).