You're driving a tractor unit fitted with 2 air lines. You want to couple to a trailer that has 3 air-line couplings. How should the air lines be connected?
- A The trailer auxiliary line should be left unconnected
- B The trailer service line should be left unconnected
- C Only the service line should be connected
- D Only the auxiliary line should be connected
Why this is the answer
A two-line system consists of the emergency line (red) and the service line (yellow). You need to understand the rules that apply to safe connection of brake systems and mixing two-line and three-line systems.
Why the other answers don't fit
- B
- The trailer service line should be left unconnected — The service line is what makes the brakes work. Leaving it off would be dangerous.
- C
- Only the service line should be connected — The emergency line must be connected as well as the service line.
- D
- Only the auxiliary line should be connected — Connecting only the auxiliary line would leave the trailer with no working brakes at all.
Where this comes from
- Driving Goods Vehicles — section 3
Rule numbers link to The Highway Code on gov.uk.
Where this question comes from
The question, its options and the explanation are reproduced word for word from the DVSA revision question bank under licence. The licence requires them to appear unaltered, so we cannot reword them and neither can anyone else — that is why you will meet the same wording on other sites. Everything else on this page is written by Theory Hub: the explanation of why each wrong answer is wrong, the topic guide and the revision notes.
Asked in: Lorry & Bus (LGV/PCV)
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