Final answer:
Chock blocks should be placed behind the downhill-facing wheels when a vehicle is parked facing downhill, and the wheels should be turned toward the curb to prevent rolling.
Step-by-step explanation:
When a vehicle is parked facing downhill, the chock blocks should be placed behind the wheels at the end of the vehicle nearest the road.
This is to ensure that if the vehicle were to start rolling, the chock blocks would stop the wheels and prevent the vehicle from moving downhill. It's essential to turn the vehicle's wheels toward the curb or side of the road so that if the brakes fail, the vehicle will roll into the curb and stop. In addition, it's advisable to engage the parking brake firmly to provide an additional safety measure against unintended rolling.