While most automatic transmission vehicles have parking brakes, it is often not engaged by drivers when parking. However, it is recommended to use it, as the parking pawl in the gearbox could fail due to stress or another vehicle striking the car, causing the car to roll. Also, regular use of the parking brake reduces the chance of corrosion by keeping the cables in-motion. In manual transmission vehicles, the parking brake can be engaged to help keep the vehicle stationary. When parking on an uphill gradient, it is recommended that the front wheels face away from the curb. This would prevent the car from rolling into the roadway by using the curb to block the front passenger tire in the event of a parking brake failure. Similarly, on a downhill gradient, the front wheels should face the curb for the same reason, and the wheels should face to the right on an uncurbed road regardless of orientation. In a manual transmission, leaving the car in first gear (or in reverse if pointing downhill) is also advised, as the engine will prevent the car from rolling if the parking brake fails.