HGV Trailers

Heavy Goods trailers come in many shapes and sizes which will depend upon the operational activity they were designed for.  The construction and operational use of the trailer will also have an effect on the width of the trailer.

The following information relating to trailers is below;

  • Weights on unbraked trailers 
  • Overall Lengths of trailers 
  • Widths of trailer 
  • Minimum ground clearance 

The following regulations apply to all trailers. Each link will take you to the relevant regulation under C&U Regulations 1986.

Trailer Overall Length 

The Construction and Use Regulations clarify which structures count towards the overall length of the vehicle. Account must be taken of any part of the vehicle, including any permanent receptacle strong enough for repeated use, and fittings on or attached to the vehicle, with the following exceptions:

  • Sheeting
  • An empty receptacle which is itself the load
  • A receptacle containing an indivisible load
  • A receptacle not over 2.5 metres in length or width
  • Lifting lugs for multi-modal transport
  • Tailboards let down to facilitate carriage but not essential to support loads extending beyond the rearmost point of the vehicle
  • Bridging plates on vehicles with trailers used to facilitate loading and unloading of vehicles carried but not to support them
  • Receptacles, other than maritime containers, manufactured before 30 October 1985 (this legalised certain existing demountable bodies)
  • Cranes, etc. that do not increase the vehicle's carrying capacity and are a permanent or essentially permanent fixture 

The regulations define "removable superstructure and standardised freight items such as containers" as being included in the vehicle dimensions regardless of whether or not they are empty. (Directive 96/53/EC Annex 1 1.4.) 

Vehicle Type 
Maximum Permitted length 

Rigid Vehicle 

12 metres 

Articulated Vehicle 

**16.5 metres 

An articulated vehicle with a low loader semi-trailer manufactured on or after I April 1991 (excluding step-frame low loaders) 


18 metres 

Car transporter semi-trailer: 

  • Kingpin to rear  
  • Kingpin to any point on the front 

12.5 metres 
4.19 metres 

Other semi-trailers: kingpin to rear 
kingpin to any point on the front 

*12 metres *2.04 metres 

Composite Trailer 

14.04 metres 

Drawbar trailer (excluding length of drawbar) provided:

  1. The trailer has four or more wheels  
  2. The drawing vehicle has a maximum gross weight of over 3,500kg 

**12 metres 

Other drawbar trailers (excluding length of the drawbar) 

7 metres 

Road-train: one trailer 
two trailers 

***18.75 metres ¥25.9 metres 

¥ Vehicle drawing more than one trailer is limited to 9.2 metres in length. 

* These dimensions include the thickness of any front or rear wall. If there is more than one kingpin position the measurement is taken from the rearmost position on semi-trailers manufactured before 1 January 1999, and from the foremost position if manufactured on or after 1 January 1999.
** No set limit if designed to carry indivisible loads of exceptional length.  

*** The distance from the foremost part of the loading area behind the cab to the rear of the trailer must not exceed 16.4 metres and this distance, less the distance between the vehicle and trailer, must not exceed 15.65 metres (this is the maximum length of the load-carrying space). The registration of new road trains with a load space length exceeding 15.65 metres was precluded under EU directive 96/53 with effect from 1 June 1998. The use of pre 1st June 1998 road trains with a load space length exceeding 15.6 5 metres will be prohibited from 31 December 2006. 

Width of Trailer 

In calculating overall width, account is taken of any part of the vehicle, any receptacle which is permanent and strong enough for repeated use, and fittings on or attached to the vehicle. The exceptions are the same as those listed previously for overall length. 

A load may not project laterally more than 305 millimetres on either side of the vehicle or trailer. The overall width of the vehicle and load must not exceed 2.9 metres. There are exceptions for indivisible loads subject to special rules, and loose agricultural produce. 

Maximum permitted width 

Provided that: 

  1. Every wheel has a pneumatic tyre 
  2. The drawing vehicle has a maximum gross weight above 3,500 kg 
  3. Every wheel of the towing vehicle (other than a locomotive) has a pneumatic tyre 

2.55 metres 

Trailers constructed to carry goods at reduced temperatures with a body sidewall thickness of at least 45 millimetres 

2.60 metres 

Other trailers 

2.3 metres 


It should be noted that one of the top five problems that occur frequently, either at roadside checks or at the annual MOT of motor vehicles or trailers, include brakes and braking systems. 

Motor vehicles and trailers first used on or after 1 April 1983 must comply with the construction, fitting and performance requirements of the EU Braking Directive with Amendments rather than the traditional construction and use requirements. The basis of assessing brake performance for enforcement, HGV testing and so on, is the same. 

All goods vehicles first used on or after 1 January 1968 must have brakes acting on all wheels capable of meeting these minimum standards at any time when on the road. 

  • Service brake - 0.5 g. 
  • Secondary brake - 0.25 g. 
  • Parking brake - holds the vehicle on a gradient of 1 in 6.25 (16 per cent) without the assistance of stored energy. 

The secondary brake can be independent of the service brake or the two can be linked through a split system. Failure of one part must still allow for at least 0.25 g retardation being provided by the other. Dual-braking systems with separate braking lines through a single pedal are also permitted. The secondary and parking brakes can be combined but, whenever a vehicle is left unattended, the minimum parking brake standard must be maintained by direct mechanical action without the use of stored hydraulic, electric or pneumatic energy. Vehicles with a vacuum or pressure braking system must generally be fitted with a device in the cab to warn of any impending failure or deficiency. 

Only one braking system with one means of operation is necessary for a works truck. 

Trailers constructed on or after 1 January 1968 must-have brakes acting on all wheels with maximum efficiencies equal to those on the drawing vehicle and emergency brakes acting on at least half the wheels and a parking brake capable of holding the trailer when stationary on a gradient not exceeding 1 in 6.25 (16 per cent). 

There are exemptions for trailers not exceeding 102 kg unladen weight manufactured before 1 October 1982, agricultural trailers, agricultural trailed appliances, broken-down vehicles and certain other trailers fitted with over-run brakes. 

A trailer with a maximum design laden weight of more than 750 kg must be braked. Inertia (overrun) type braking system may be used up to a maximum permissible laden weight of 3,500 kg. 

A trailer manufactured before 1 January 1997, and which has a maximum total design axle weight not exceeding 750 kg, is not required to have brakes or a safety secondary coupling device. Trailers manufactured from 1 January 1997 with a maximum total design axle weight not exceeding 750 kg are not required to have brakes but must have a safety secondary coupling device. If brakes are fitted then they must comply with EU Directive 91/422. 

A Divisional Court case held that if a trailer is fitted with brakes, they must be inefficient working order, even if the trailer is not required by law to have brakes 

Braking & Safety Coupling Information – Trailers 

Trailer total maximum design axle(s) weight 
Braking Requirements 
Coupling Safety Measure - Requirement 

Less than 750 kg 


Pre-1997 no requirement for ‘secondary coupling’ 

A post-1997 requirement for ‘secondary coupling’ 


If brakes are fitted – usually mechanical (inertia). 

Pre-1997 no requirement for either ‘breakaway device’ or ‘secondary coupling’ 

A post-1997 requirement for either ‘breakaway device’ or ‘secondary coupling’ 

750 – 1,500 kg 

Must have brakes – usually mechanical (inertia). 

Either ‘breakaway device’ or ‘secondary coupling’ 

1,500 – 3,500 kg 

Must have brakes – usually mechanical (inertia). 

‘Breakaway device’ usually a ‘breakaway cable’. 

Over 3,500kg 

Must have power brakes (pneumatic, etc.) 

Device to automatically apply breaks in the event of a separation of the main coupling ‘Breakaway device’. 

Breakaway Device 

In the event of a trailer de-coupling from a towing vehicle, the brakes will come on automatically. 

Secondary Coupling 

In the event of trailer de-coupling from a towing attachment on a towing vehicle, there is a second connection (cable, chain, etc.) which keeps trailer attached to the vehicle. 

Anti-lock Brakes 

Anti-lock braking systems must be fitted to the following goods vehicles:

  • Motor vehicles first registered on or after 1 April 1992 with design gross vehicle weight greater than 16,000 kg and authorised to tow trailers with total design axle weight exceeding 10,000 kg. 
  • Trailers with total design axle weight exceeding 10,000 kg manufactured on or after 1 October 1991. 
  • New N3 models from 1998 where required to have anti-lock braking fitted as part of their type approval. All N2, N3, 03 and 04 vehicles registered from 1 April 2002 are required to have anti-lock braking systems fitted. 

The anti-lock systems must comply with the EU braking directive with amendments. 

Regulation 18 of the Construction and Use Regulations permits the completion of a journey in a vehicle with a faulty anti-lock braking system if the fault arose en-route, or to drive the vehicle to a place where the fault is to be repaired. However, under section 69 of the Road Traffic Act legislation, DVSA (Driver and Vehicle Standards Agency) may prohibit the vehicle from being used on the road if it appears to a goods vehicle examiner that, owing to any defects in the vehicle, it is, or is likely to become, unfit for service. 

DVSA enforcement officers have traditionally issued a prohibition notice for any ABS related defects at roadside checks, even if the fault occurred during the journey. However, FTA challenged DVSA on this action, as in certain circumstances operators were being issued with prohibitions and associated OCRS points for ABS Malfunction Indicator Lamp faults which became illuminated during a journey, at the start of which the ABS was functioning correctly, as this was not in line with the letter and spirit of the Road Vehicles (Construction and Use) Regulations 1986, Regulations 18 (1A) and (1B). 

Tractor-trailer ABS Connector 

Vehicles first used on or after 1 May 2002 and trailers over 3,500kg manufactured on or after May 2002 must be fitted with ISO 7638 connections. 

Also, from 1 May 2002 an amendment to construction and use specifically requires that when both the tractor unit and the trailer are fitted with the ISO 7638 ABS sockets then the IS07638 connector must be fitted between them. The alternative of powering via the 24N or 24S sockets is not permitted. DVSA will issue a PG9 if the connector is not fitted. Many new trailers, especially those fitted with disc brakes and electronic braking, are no longer fitted with the naming lights on the front offside of the trailer. Provided the dedicated anti-lock braking connector is fitted, this does not present a problem as the warning lights provided on the tractor unit will indicate a fault on the trailer. 

If a tractor unit that is not fitted with the dedicated ABS socket, is coupled to one of these later trailers, the driver will not see the operation of the anti-lock braking on the trailer. Operators should therefore take care that older tractor units, which do not have the dedicated anti-lock braking connector, are not coupled to the latest generation of trailers as the driver would have no indication of an ABS fault on the trailer and this would result in the issue of PG9 at roadside checks. 

Electronic braking systems 

Many modern vehicles and trailers are fitted with Electronic Braking Systems (EBS) as standard. These systems can simultaneously fulfil the operation of an anti-lock system (ABS) and a load sensing system with superior reaction time. If both vehicle and trailer are fitted with EBS, the two systems can communicate via a data link and offer the potential of improved tractor/ trailer compatibility and in the case of vehicles can also provide Anti-Slip Reduction (ASR) 

Trailers fitted with EBS are typically identifiable by the presence of a seven-pin ISO 7638 socket on the trailer, and possibly a manufacturer's headboard plate. All ABS and EBS vehicles and trailers approved to UN or EC requirements must display a warning lamp to indicate to the driver the existence of a fault, and this can be in the form of a warning lamp on the vehicle which can either be an ABS or EBS (or both) warning lamp. 

For roadside enforcement purposes, DVSA distinguish between ABS and EBS fitted to trailers, and the sanction level applied is different for the two systems being more severe in cases where EBS warning lamps are inoperative or indicating the existence of a fault. Full details of DVSA's sanction policy is detailed in DVSA's Categorisation of Defects publication which can be downloaded at the link below. 

Automatic Brake Adjusters 

Almost all goods vehicles with a gross mass over 3.5 tonnes first used on or after 1 April 1995 and all trailers with a gross mass over 3.5 tonnes manufactured after 1 April 1995 must be fitted with automatic brake adjusters. Light goods vehicles (category N1) first used on or after 1 April 1995 are required to have automatic brake adjusters on the front axle 

Minimum Ground Clearance 

Trailers subject to the minimum ground clearance rules must keep to the minimum at all times when in use on a road. Exceptions are provided:

  • for a trailer fitted with a suspension system with which it may be lowered or raised: 
  • whilst that system is being operated to enable the trailer to pass under a bridge or other obstruction; and 
  • as long as no part of the trailer (excluding wheels) touches the ground or is likely to do so; or 
  • while loading or unloading 

To minimise the risks of grounding on railway level crossings etc., every trailer manufactured on or after 1 April 1984 must meet minimum ground clearance rules. There must be a minimum ground clearance of 160 millimetres if the trailer has an axle interspace of more than 6 metres but less than 11.5 metres, and a minimum clearance of 190 millimetres if the trailer has an axle interspace of 11.5 metres or more. 

The following link provides guidance and further information

The Trailer Registration Regulations 2018