A parking brake interlock is provided according to the invention. The parking brake interlock includes a parking brake inlet configured to receive a parking brake air supply, a service brake inlet configured to receive a service brake air supply, an exhaust port, and an interlock valve mechanism in communication with the parking brake inlet, the service brake inlet, and the exhaust port. The interlock valve mechanism is configured to exhaust the parking brake air supply if the service brake air pressure is not received. The interlock valve mechanism is further configured to hold the parking brake air supply in order to generate a parking brake air pressure if the service brake air pressure is received.