A motor vehicle speed control system which, upon activation by the vehicle operator, maintains the vehicle at a predetermined set speed. The system utilizes a duty-cycle type pneumatic servoactuator responsive to an electrical control signal for controlling movement of the vehicle throttle. Control means responsive to deviation of vehicle speed from the predetermined set speed, is operable to vary the control signal characteristics in accordance with a predetermined governing equation and the electrical control signal is utilized to operate the servoactuator. Vehicle speed is sensed by a generator providing an electrical signal output and a control means is of the electronic type responsive to the electrical speed signal and the predetermined set speed. In one embodiment both analog-digital circuit techniques are employed for the control means and, in another embodiment, substantially all-digital circuitry is utilized.