After selecting the proper low gear, how should you use the service brakes on a long, steep downgrade?
Correct answer: C. – Brake to about 5 mph below the safe speed, release, and repeat when speed returns
Use engine braking as the principal means of controlling speed and select the proper low gear before descending. Apply the service brakes firmly enough to produce a definite slowdown. After reducing speed to about 5 mph below the selected safe speed—normally during an application lasting about three seconds—release the brakes and repeat when the vehicle returns to the safe speed.
Source: Arkansas Commercial Driver License Manual — § 2.16.4, “Proper Braking Technique”

