A throttle control system and method for use with a vehicle. The throttle control system receives an input voltage from a vehicle throttle controller. The throttle control system prepares a throttle signal and provides the throttle signal to the throttle to force deceleration to a selected speed or constrain acceleration to a selected value. Preparing the throttle signal may follow detection of maximum threshold values of speed or input voltage. The maximum threshold values may be specific to the location of the vehicle. The throttle signal and the maximum threshold values may be defined with reference to the input voltage, vehicle speed, vehicle location, or other parameters. The throttle signal may force deceleration or constrain acceleration incrementally to mitigate loss of vehicle throttle controller responsiveness to driver commands. The throttle signal may be an output voltage provided to a vehicle electronic control module.