What is the maximum legal trailer length for a car-towed trailer in Northern Ireland?

For a trailer towed by a vehicle up to 3.5 tonnes, nidirect gives a general maximum trailer length of 7 metres in Northern Ireland.

This is a specifically Northern Ireland question because the applicable road rules, DfI/DVA processes and Northern Ireland Highway Code are the relevant reference point. That figure concerns the trailer body in the ordinary towing rules; special combinations and vehicle classes can have different construction-and-use limits.

For this exact issue — “What is the maximum legal trailer length for a car-towed trailer in Northern Ireland?” — separate four things that are often confused: the entitlement on the NI driving licence, the trailer’s plated MAM, the towing vehicle’s manufacturer limits and the actual laden weight of the combination. Insurance and roadworthiness sit on top of those limits; meeting one figure does not make an otherwise overweight, unbraked or uninsured setup lawful.

Do not forget that legal length does not guarantee the towing vehicle is rated for the trailer. Weight, coupling and licence limits still apply. If signs, licence categories, vehicle plates or official instructions conflict with something remembered from an older guide, follow the current official information and the live road signs.

Before publishing this answer, the key factual point in “What is the maximum legal trailer length for a car-towed trailer in Northern Ireland?” was checked against current Northern Ireland official guidance. That matters because road rules, licence entitlements and enforcement details can differ from Great Britain and can change over time; the sources attached below are the ones to re-check if the rule is updated.