Final answer:
On a downgrade, wheels should be turned towards the edge of the roadway to prevent the vehicle from rolling into traffic if the brakes fail.
Step-by-step explanation:
When parking on a downgrade, one should turn their wheels towards the edge of the roadway. This parking technique ensures that if your vehicle's brakes were to fail, the car would roll into the curb or the edge of the roadway, potentially stopping it from moving into traffic. It is essential to be aware of one's surroundings and use relative directions to secure the vehicle properly when parking on an incline or downgrade.