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CDL · Communicating

When should you flash your brake lights to warn drivers behind you?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Tap the brake pedal lightly to flash the lights when you are about to slow suddenly or when stopped traffic is ahead

  1. A Only when the vehicle behind is tailgating
  2. B Tap the brake pedal lightly to flash the lights when you are about to slow suddenly or when stopped traffic is ahead
  3. C Continuously while traveling under the speed limit
  4. D Never; brake lights should come on only when slowing

Why this is the answer

Tapping the brake pedal lightly to flash the brake lights is a deliberate warning to following drivers when you are about to slow significantly, when there is a traffic jam ahead they may not see, or when an obstacle requires you to brake harder than usual. The early warning gives the driver behind extra seconds to react. This is especially important in commercial vehicles because following drivers often misjudge how quickly a heavy vehicle can slow and tailgate accordingly. Flashing brake lights when stopped or barely moving in traffic communicates to drivers approaching from behind that they need to slow. Continuous brake light operation when not braking is illegal and confusing.
Source: FMCSA CDL Manual 2.5.2 Communicating Trouble Ahead

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About this topic: Communicating

Other road users cannot read your mind. Turn signals, brake lights, headlights, and the horn are how you tell them what you are about to do — used correctly, they prevent crashes. This is one of 3 General Knowledge questions on communicating, each with a full explanation on a single study page.

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