Accelerating gear (overdrive).
Some cars use gearboxes with additional accelerator gears, called overdrive. Such a gearbox is usually a separate unit in the form of an attachment to the ordinary gearbox. When an overdrive is engaged, the propeller shaft turns faster than the clutch shaft, thanks to which the speed of the car's movement is greater than in direct gear. The overdrive is only activated under good driving conditions, e.g, on the highways, when the resistance to motion is low. Sometimes the accelerator gears are built into the gearbox. Using the overdrive allows you to drive fast with reduced fuel consumption.