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Incorrect!

You're driving an articulated lorry that has 3 air lines connected to the trailer. What's the purpose of the red line?

It's the emergency line
Correct answer
It's the service line
It's the auxiliary line
It's the electrical line
You selected this answer

DVSA theory test explanation

The red emergency line is common to both two-line and three-line brake systems. The other colours are blue (for the auxiliary line) and yellow (for the service line).

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