While operating a fully loaded combination vehicle in sub-freezing temperatures, you approach the crest of a long, steep mountain downgrade. The road surface is visibly slick with patchy ice, and an advisory sign indicates a truck safe speed of 25 mph. Which of the following describes the correct, comprehensive procedure for executing this descent safely?
- ALeave the engine retarder engaged on a minimum setting to assist the service brakes, select a low gear before the descent, and apply steady, continuous pressure on the brake pedal to maintain exactly 25 mph.
- Turn off the auxiliary retarder, engage a lower gear than was used to climb the grade before crossing the crest, and firmly apply the service brakes at 25 mph until the vehicle slows to 20 mph.Answer
- CDeactivate the auxiliary retarder, begin the descent in the same gear used for climbing, and allow gravity to accelerate the vehicle to 30 mph before applying the service brakes firmly to reduce speed back to 25 mph.
- DTurn off the engine retarder, initiate the descent to evaluate road traction before attempting to downshift, and maintain a continuous, light brake application to keep your speed safely at 20 mph.
Answer
The correct procedure is to turn off the retarder, select a lower gear before crossing the crest, and use the snub braking technique by applying the brakes firmly at 25 mph until the vehicle slows to 20 mph.
The correct answer perfectly addresses all three hazard factors: it eliminates the risk of a drive-wheel skid by turning off the retarder on ice, secures engine braking by downshifting before the downgrade begins, and preserves the service brakes by correctly executing the snub braking cycle from the 25 mph safe speed down to 20 mph.
Step-by-Step Solution
Key Concept
Complex mountain descents require a precise synthesis of retarder management for traction, proactive gear selection for engine braking, and disciplined snub braking to prevent brake failure.
Estimated Time:1m 30s