Abstract: A speed adjusting system for vehicles includes an accelerator, such as a throttle pedal, a speed adjusting device, such as a throttle or a fuel injection pump, which is adjustable by operating the accelerator, and a control unit which is connected to the accelerator and which is settable between a first operating position, in which the accelerator is operable without difficulty, and a second operating position, in which the accelerator is operable with difficulty. The second operating position constitutes a basic state of the control unit, the difficulty, with which the accelerator is operable when the control unit is arranged in the basic state, appearing as a resistance which is generated by the control unit and acts on the accelerator and which must be overcome for operating the accelerator and which clearly exceeds the resistance that exists for operating a conventional accelerator.