Final answer:
If a vehicle's conventional disc and drum brakes suddenly fail, a motorist should use alternative braking techniques such as engaging the emergency or parking brake, downshifting to a lower gear in a manual transmission vehicle, or utilizing natural obstacles to slow down the vehicle.
Step-by-step explanation:
If a vehicle's conventional disc and drum brakes suddenly fail, a motorist should use alternative braking techniques to slow down and stop the vehicle. One common technique is to engage the emergency or parking brake, which can sometimes provide enough braking force to bring the vehicle to a stop. Another technique is to downshift to a lower gear in a manual transmission vehicle, which uses the engine's resistance to help slow down the vehicle. Additionally, the motorist can also look for a safe area to pull over and use natural obstacles, such as sand or gravel, to help slow down the vehicle.