Final answer:
When parking up a hill with a curb, turn your wheels away from the curb if uphill and towards the curb if facing downhill to ensure the vehicle does not roll into traffic.
Step-by-step explanation:
When you are parking up a hill with a curb, the correct way to place your wheels depends on whether you are facing uphill or downhill. For uphill parking, turn your front wheels away from the curb and then roll back a little bit so the rear of the wheel touches the curb. This prevents the car from rolling into traffic if the brakes fail. Conversely, when facing downhill, turn your wheels towards the curb, and again, allow the car to roll back until the tire rests against the curb. The idea is to use the curb as a barrier in case the parking brake or the regular brakes do not hold.
Remember that when there's no curb, you should always turn your wheels so that if your car starts to move, it will roll off the roadway rather than into traffic. The use of the curb is to ensure that the vehicle remains stationary and that you've taken vehicle safety precautions, reducing the risk of your parked vehicle becoming a hazard.