Before starting down a steep grade, what should a CMV driver do?

Selecting a LOWER GEAR BEFORE the descent is one of the most critical mountain driving safety rules. WHY BEFORE, NOT DURING: Once a heavy vehicle begins descending a grade at speed, the kinetic energy is enormous — the engine compression braking effect is minimal unless the drivetrain is in a low enough gear. Attempting to downshift while rolling fast down a steep grade often results in failed shifts (grinding, inability to engage gear) because the engine RPM and road speed are mismatched. The vehicle then continues accelerating with no engine braking.

Which gear to select: Use a gear lower than you would use to climb the same grade at the same speed. If you'd climb in 4th gear at 30 mph, descend in 3rd or lower. Check for posted advisory speeds and maximum grade percentage signs — these give guidance.

The speed-selection principle: Select a speed you are confident you can hold throughout the descent using engine braking + occasional brake taps, without sustained brake application. Sustained brake application leads to brake fade.

Stab braking for descent: Hard brake application (building pressure) → release completely → let brakes cool → hard application again. Never ride the brakes lightly for extended periods.

Runaway truck ramps: Escape ramps are built into steep grades for vehicles that have lost braking control. Know they exist and be willing to use one — it's not a failure, it's a life-saving tool.