An automatic vehicle braking system prohibits vehicle propulsion upon detection of a triggering event, and includes sensors that detect the triggering event, a processor. A logic gate and a vehicle gear sensor cooperate with the processor to automatically activate and deactivate a vehicle braking system, which includes a solenoid switch responsive to an output signal from the logic gate. An air valve is activates the vehicle braking system by permitting air to pass downstream of the air valve and to existing vehicle brake pads. An outlet port is situated downstream from the inlet port of the air valve casing. A piston is linearly reciprocated within the casing such that the inlet port is in fluid communication with the existing air tank of the vehicle. In this manner, the outlet port may be adapted to be in fluid communication with an existing brake pad of the vehicle braking system.