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What is the correct coupling & uncoupling code of practice


HSE SOE/IRTE Recommended Coupling/ Uncoupling Procedures for Standard Semi Trailers

This procedure should be adopted whenever there is adequate room between the rear of the tractor unit cab and the front of the semi trailer, when coupled, for the driver to work in safety. The driver must be advised of and understand the potential dangers to themselves and others when deviating from an approved procedure.


Slowly reverse the tractor unit in a straight line towards the front of the trailer. Stop when the bottom of the 5th wheel ramps are level with the front of the trailer. Apply the tractor unit parking brake, stop the engine and remove the keys.

Check the trailer parking brake is applied. Do not walk under the trailer.

Inspect the 5th wheel and locking devices on the tractor unit, plus the king pin and rubbing plate on the trailer for any signs of damage. Assuming everything is in order move to the next stage. Should any damage be apparent do not continue, but seek assistance.

Check and, if necessary, adjust the trailer coupling height relative to the 5th wheel, which is normally designed to accept the king pin just below its parallel height. Refer to the manufacturer's instructions for the correct procedure. Height adjustment may be achieved by extending or retracting the trailer landing legs. Changing the tractor unit height, if it is equipped with air suspension, is an alternative solution. If this process is not carried out correctly and the trailer is too high, in some cases it is possible to miss the 5th wheel jaws completely, so that the king pin passes over it into a dangerous position behind the cab or rests on top of the 5th wheel.

Slowly reverse the tractor unit under the trailer until the 5th wheel jaws engage. Apply the tractor unit parking brake, stop the engine and remove the keys.

To check the 5th wheel jaws have correctly engaged, carry out a visual inspection to verify that the king pin is correctly located in the jaws and that the 5th wheel release handle is in the correct ‘locked’ position. Fit the security ‘dog clip’ and/or any other safety device provided.

Note: If the dog clip does not fully engage, pull release handle to disengage the jaws and slowly move tractor unit away from trailer, then repeat the 5th wheel coupling procedure.

The second test is to select a low forward gear and with the trailer brakes still applied, slowly pull forward and perform a ‘snatch test’. Repeat the snatch test to confirm the jaws have locked. Apply the tractor unit parking brake, stop the engine and remove the keys.

Connect the service air line (yellow) and electrical connections.

Connect the emergency air line (red) and watch for any unexpected movement.

Note: If the trailer moves, immediately disconnect the emergency air line (red) and check that the trailer parking brake has been applied.

Wind up the landing legs and stow the handle. Release the trailer parking brake, ensure that any air suspension control is set to the ‘ride’ position and attach the rear number plate.

Test the operation of all of the lamps.

Before pulling away walk around the combination to check that everything is in order. Checks should include; the routine requirements of oil, water, fuel, windscreen, mirrors, truck and trailer wheels and tyres for security and legality, bodywork and ancillary equipment. It is also the responsibility of the driver to check that the load is secure and that the in-cab height indicator is correct. The driver should turn on the ignition to check that the ABS/EBS warning lamp(s) activate in the correct sequence and extinguish. If for any reason the combination appears unroadworthy, do not proceed, but seek assistance.

On pulling away, test the brakes to ensure correct operation and that, if fitted, the ABS warning lamp on the trailer functions correctly and extinguishes when a speed of 15 kph is exceeded.


Park the combination in a straight line. Apply the tractor unit parking brake, stop the engine and remove the keys.

Apply the trailer parking brake.

Remove the trailer number plate and place in the stowage position provided or in the cab.

Lower the landing legs until they are in contact with the ground.

Disconnect all of the air and electrical services. When disconnecting the emergency air line (red) grip the connection firmly as it may kick back when released due to the air pressure in the line.

Note: Do not leave the connections loose, but place them in the dummy stowage positions provided or secure them on the 'cat walk' in such manner that water and dirt cannot enter the connections.

Remove the security dog clip and any other safety device, then pull the release handle to disengage the 5th wheel jaws.

Slowly draw the tractor unit away from the trailer. If the tractor unit has air suspension stop after approximately 300mm and apply the tractor unit parking brake whilst the 5th wheel is still under the trailer rubbing plate, and lower the rear axle air suspension to drop the 5th wheel away from the trailer. Lowering the suspension will prevent the rear of the tractor unit rising suddenly as the trailer weight is removed from the fifth wheel. Then pull clear of the trailer and stop. Reset the tractor unit air suspension to the ride position. If the tractor unit has mechanical suspension, stop when the trailer is clear of the 5th wheel. Apply the tractor unit parking brake, stop the engine and remove the keys.

Before leaving the trailer, walk around it and check that it is in a safe condition.


This content is extracted from the more comprehensive HSE SOE/IRTE Code of Practice for Coupling or Uncoupling & Parking of Large Goods Vehicle Trailers: Guidance for managers, supervisors & trainers.

Published: Fri 20 Apr 2018

Updated: Fri 12 Apr 2024

Don-Bur (Bodies & Trailers) Ltd

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