Legally, What Is The Biggest Trailer?

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Accepted Answer

Trailer dimensions are governed by The Road Vehicles (Construction In Use) 1986.

Body width is either 2550mm for dry freight or 2600mm for temperature controlled bodywork.

In isolation, trailer length is governed by a combination of 2 dimensions.

The length from the kingpin to the trailer rear must not exceed 12m
The forward swing radius from the kingpin must not exceed 2.040m

As trailer manufacture differs between both body types and brand, this means that trailer length can vary. Typically, a curtainsider will be a maximum overall length of 13.7m and a box van trailer will have a maximum overall length of 13.6m; however, by altering the shape of the front bulkhead, dimension 2) as described above, can be manipulated to increase overall length.

Additionally, the maximum tractor/trailer overall combination length of 16.5m cannot be exceeded. Whilst tractor units and fifth wheel positions are typically designed to provide sufficient space for a full-length trailer, a longer tractor unit cab length or a longer fifth wheel position (set further back) will increase combination length and this will therefore restrict the maximum length of the trailer.

Within the EU, maximum trailer height is 4m. In the UK, there was a derogation for overall height; removing this restriction completely. This means that trailer for UK use can be designed to any practical height. Typically, double deck trailers tend to have a maximum height of 4.95m to provide sufficient clearance under unmarked bridges.

Longer Semi Trailers (LSTs)

The use of Longer Semi Trailers, under an amended STGO regulation, came into force on 31st May 2023 and permits operators to use them in general circulation with some legal restrictions and guidance.

LSTs can be up to 15.65m long from the foremost point of the load space to the rear and where the total combination length does not exceed 18.55m. This means that up to 4 additional UK pallets (1200x1000mm) can be loaded per deck, up to a maximum total of 60 UK pallets on a double deck version.

Further details can be found here.

Longer Heavier Vehicles (LHVs)

The terms LHV refers to a B double combination where an additional special trailer with an extra fifth wheel mounted on an extended rear chassis is placed between a standard tractor and full length trailer.

The resulting combination is 25.25m long and requires steered axles to achieve turning circle regulations.

LHVs are being considered by the DfT but are not currently legal to operate on UK roads.