Revision question · Braking systems

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

Revision material from the imported DVSA bank includes source-checked Lanekind learning corrections. These corrections are not newly issued official examination questions, and practice does not reproduce a live test paper.

Answer options

It's the emergency line

It's the service line

It's the auxiliary line

It's the electrical line

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It's the emergency lineThis was the right answer

The red emergency line is common to both two-line and three-line brake systems. The other colours are

• blue - auxiliary

• yellow - service.

Reviewed reading for this question

Keep trailer connections and parking brakes distinctReviewed guidance summary · Both questions specifically identify the red emergency line; the guide does not invent the obsolete third-line procedure.

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