The impetus is to minimize overdrive use and provide a higher ratio first gear, which means more gears between the first and the last to keep the engine at its most efficient speed. This is part of the reason that modern automobiles tend to have larger numbers of gears in their transmissions. It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i.e. where high (numerical) differential gear is required to get the vehicle moving as in trucks or performance cars though double overdrive transmissions are common in other vehicles, often with a small number on the axle gear reduction, but usually only engage at speeds exceeding .