Final answer:
When parking downhill with a curb, the vehicle's wheels should be turned towards the curb to prevent the car from rolling into traffic if the parking brake fails.
Step-by-step explanation:
When parking on a hill with a curb and facing downward, the wheels of your vehicle should be facing towards the curb. This action will ensure that in the event of a failure in the parking brake, the vehicle would roll into the curb and stop, instead of rolling into the street. It is a safety measure that prevents the vehicle from becoming a hazard on the road.