While transporting a 78,000-pound load down an 8-mile, 5% mountain grade, you establish a safe speed of 40 mph based on the vehicle's weight and the grade's steepness. You have placed the transmission in the appropriate low gear prior to the descent and are utilizing a multi-stage engine retarder set to maximum power. Initially, the pavement is dry, and you are successfully applying the brakes firmly at 40 mph and releasing them at 35 mph. Two miles into the descent, you encounter a heavily shaded section of the mountain where the road surface is suddenly covered in packed snow and ice. Which of the following describes the most critical and immediate sequence of adjustments you must execute to prevent a loss of vehicle control?
- ALeave the engine retarder engaged to avoid relying on the service brakes on the slick surface. Simultaneously, abandon the intermittent braking technique and apply a continuous, very light pressure to the brake pedal to maintain a steady speed without sudden weight shifts.
- BDeactivate the engine retarder to regain traction. Firmly apply the service brakes to bring your speed down to 20 mph, then quickly attempt to double-clutch into a lower gear to maximize engine braking without relying on the retarder.
- CMaintain the engine retarder on its maximum setting to ensure maximum auxiliary resistance. To prevent the trailer wheels from locking on the ice, avoid using the service brakes entirely until you reach dry pavement again.
- Immediately switch off the engine retarder to prevent the drive wheels from losing traction and causing a skid. Rely solely on the mechanical engine braking provided by your current low gear, and continue utilizing the established firm braking cycle from 40 mph down to 35 mph as needed.Answer
Answer
The driver must immediately turn off the engine retarder to prevent a skid and continue using the proper snub braking technique (braking firmly from 40 mph to 35 mph) in the current gear.
When road conditions become slippery (such as encountering packed snow and ice), the engine retarder must be turned off immediately. Retarders apply braking resistance exclusively to the drive wheels, which can easily induce a loss of traction and a skid on slick surfaces. Furthermore, the driver must rely on the low gear established before the descent and strictly maintain the proper snub braking technique (applying brakes firmly to reduce speed by 5 mph, then fully releasing them) to prevent the brakes from overheating and failing.
Step-by-Step Solution
Key Concept
Managing Retarders and Snub Braking Under Changing Environmental Conditions