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General Knowledge · Mountain Driving

What is the correct way to choose a safe speed before starting down a long, steep downgrade?

1.Choose a speed low enough that you will not need continuous heavy braking to control it for the whole grade, and set it before starting downCorrect answer
2.Start down at the posted highway speed limit and reduce speed only once the vehicle starts to feel unstable or the brakes begin to feel soft underfoot
3.Match your descending speed to the speed you could safely hold on level ground in top gear while carrying that same load
4.Start down at any speed and adjust afterward, using the service brakes as the primary way to control speed the whole way down

Explanation

The correct practice is to select a speed low enough that the vehicle can be controlled for the entire length of the grade without relying on continuous, heavy brake use, and to make that choice before starting down, not partway through. 49 CFR 383.111(a)(19)(i) names selecting a safe speed as required knowledge but does not itself state a formula or number, so the specific practice is standard driver-training content, attributed to the manual rather than the regulation. The wrong options share the same underlying failure: each treats the brakes, or an unrelated speed limit, as the primary means of controlling the descent, when the point of selecting a safe speed in advance is to avoid depending on the brakes at all.

Source: 49 CFR 383.111(a)(19)(i)

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