Trailer dimensions in the UK are governed by the Road Vehicles (Construction and Use) Regulations 1986 (as amended), supported by retained EU-derived law such as SI 2020/1393 and SI 2022/59. These mirror aspects of Directive 96/53/EC and related regulations on vehicle dimensions and aerodynamic improvements.
Trailer Width
- 2,550 mm — standard dry-freight trailers
- 2,600 mm — temperature-controlled trailers with insulated bodywork
Trailer Length
Two statutory parameters define trailer length:
- Kingpin to rear: must not exceed 12.0 m
- Forward swing radius: kingpin to foremost point of trailer must not exceed 2.040 m
Within these bounds, overall trailer length varies by body type and design. For example:
- Curtainsiders — up to ~13.7 m overall
- Box vans — typically around 13.6 m overall
Manufacturers can optimise length by shaping the front bulkhead to minimise swing radius.
Overall Combination Length
Standard articulated combinations are capped at 16.5 m. This envelope depends on tractor design, fifth-wheel position and trailer geometry. For a full explanation of how these limits interact — including elongated cabs and rear aerodynamic devices — see our companion article:
Articulated Vehicle Length Allowances
Trailer Height
- EU: maximum height 4.0 m
- UK: no legal maximum, owing to a long-standing derogation
This permits double-deck trailers up to ~4.95 m in practice, while still observing bridge clearances.
Longer Semi-Trailers (LSTs)
As of 31 May 2023, LSTs are legal for general use. Key limits:
- Trailer length: up to 15.65 m
- Overall articulated length: up to 18.55 m
This enables ~4 additional UK pallets per deck — up to 60 pallets on a double-deck LST.
Aerodynamic Devices & Cab Extensions
Additional length may be permitted where it improves aerodynamics or safety, provided it does not increase usable load space. Allowances include:
- Rear devices: up to 500 mm (e.g. boat-tails/flaps), retractable or foldable
- Sides: up to 25 mm per side (2,600 mm overall)
- Cab elongations: no fixed mm cap — permitted if type-approved under Article 9a of Directive 96/53/EC
For detailed analysis of these rules — and how they can extend beyond 16.5 m — see our article:
Articulated Vehicle Length Allowances.
Turning Circle Compliance
Whatever the length, combinations must still meet manoeuvrability requirements (inner radius 5.3 m, outer radius 12.5 m). On the trailer side, this equates to an 8,135 mm wheelbase limit for a 2.55 m trailer. See our full guide:
Trailer Turning Circle Requirements
Longer Heavier Vehicles (LHVs)
“B-double” or LHV combinations (tractor + intermediary dolly + full-length trailer) measure up to 25.25 m and require steered axles to comply with turning rules. These are not currently legal in the UK but remain under Department for Transport review.
