A parking transaction system uses a vehicle on-board diagnostics system and sensors to determine when a vehicle has parked in a designated parking zone. The determination may occur by monitoring engine or motor status sensors, geolocation sensors, and/or other in-vehicle sensors to determine whether the vehicle in an energy-efficient state while in a known parking zone. When the vehicle is parked in a designated parking zone and in an energy-efficient state, the vehicle's system will initiate a parking transaction for a minimum period of time. If the vehicle sensors indicate that the vehicle has not moved out of the energy efficient state and away from the parking zone before the time period ends, the system will automatically extend the parking transaction for one or more additional time periods.