When you park facing downhill, turn your front wheels toward the curb (or toward the side of the road if there is no curb). By doing this, if your car were to roll, it would roll into the curb and stop, rather than rolling out into traffic.
Here’s the procedure:
Before turning off the car, turn the steering wheel all the way so that your front tires point toward the curb. If there’s a curb, your front tire should gently touch it. If there’s no curb, turning the wheels toward the side of the road means if the car rolls, it will go off the roadway, not into it.
Shift the car into Park (for an automatic) or into reverse gear (for a manual transmission, when facing downhill).
Set the parking brake firmly.
This way, you have multiple safeguards: the transmission/gear, the parking brake, and the wheel turned into the curb as a fail-safe. On a downhill, the curb is in front of your wheels, so that’s why you turn toward it. (For completeness: if you were facing uphill with a curb, you’d turn wheels away from curb; if uphill with no curb, toward the side of road. But facing downhill, always toward the curb.)
So the direct answer: turn your wheels toward the curb when parked downhill. This will prevent your vehicle from rolling into traffic if your brakes were to fail. Always remember to use your parking brake as well.
