Abstract: A vehicle speed limiter is described, for use with, and for example fitted to, a vehicle throttle system (1) comprising a mechanically actuatable throttle member (3), an engine (10) speed controller (7), and a throttle signal unit in data communication with an engine speed controller and operably coupled to the throttle member so as to generate an electronic throttle signal in functional response to the degree of actuation of the throttle member, and to transmit a throttle signal to the engine speed controller whereby the engine speed is controlled.