Before beginning a steep downgrade, how should you select your transmission gear?
Correct answer: B. – Select a low gear before the descent, usually lower than the gear used to climb the hill
The Georgia CDL guide instructs drivers to slow down and shift into a controllable low gear before starting downhill. The gear will usually need to be lower than the one required to climb the same hill. Engine braking should be the main method of controlling downgrade speed, preserving the service brakes for necessary slowing or stopping.
Source: Georgia Commercial Driver’s Study Guide — § 2.3.1, “Before Starting Down a Hill”; § 2.6.6, “Speed on Downgrades”

