Trailer Maximum Weights

Type 1: This applies to un-braked trailers – maximum 750kg gross trailer weight or half of the towing vehicle’s kerb weight. Focus on whichever is less.

Type 2: This applies to trailers on overrun brakes – maximum 3500kg gross trailer weight.

Regulations issued in 1982 state that all trailers, including un-braked ones, must have their maximum gross weight in kg clearly marked and visible. The police may check this at any time at a weighbridge. The year of manufacture must also be shown on un-braked trailer plates following the introduction of this law in January 1997. 

For the recall of defective trailers less than 3500kg maximum gross weight, to comply with the D.O.T Code of Practice, it is necessary that the trailer should carry a manufacturer’s plate clearly showing the following;

o Manufacturer’s name and address, chassis or serial number and model number.
o Date of Manufacture
o Number of axles
o Maximum weight per axle 
o Nose weight of coupling
o Maximum Gross Weight 

Maximum Dimensions

Towing vehicle under 3500kg maximum gross weight

Length - (excluding the drawbar and coupling) 7.0 metres 
Width Maximum 2.3 metres

Towing Vehicle over 3500kg maximum gross weight

Length – (excluding the drawbar and coupling) 12 metres
Width Maximum 2.55 metres
Combined length of towing vehicle & trailer 18 metres
Maximum overhang of load from rear of trailer 3.05 metres

Marking of rear overhang

Between 1m and 2m, the end must be clearly visible, do so by attaching a piece of cloth or similar. 

Between 2m and 3.05m, a marker board as defined in the regulations must be fitted and also illuminated at night.

If the overhang is greater than 3.05m, an attendant must be carried and it is essential that the police are notified two days prior to commencing the journey.

"Long Vehicle" Marker Plate: This is not necessary for light trailers. 

These are a legal requirement only for trailers over 3500kg or where the towing vehicle is greater than 7500kg gross weight. When they are required, different plates are needed depending on the length of the vehicle. Further details can be found in the Road Vehicle Lighting Regulations, Schedule 18. 

Loads must not extend more than 305mm either side of the trailer, up to a maximum width of 2.9m. 

Loads greater than 2.9m in width are classed as abnormal loads and the police must be notified two days prior to the journey commencing. 

Recommended maximum height: 

3.0m high or 1.7 times the wheel track. (Horizontal distance between centre lines of tyre treads) 

There is no legal requirement, but this is an accepted guideline.

However if the height does exceed 3.0m then a notice giving the height details must be displayed in the cab of the towing vehicle. Buses are the only vehicle subject to a maximum height regulation.