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Technical bulletins

6 Certification of light vehicles towing heavy trailers

This technical bulletin replaces memo 67.

When an HVEK certifier is presented with an electric-braked TC trailer towed by a light vehicle, the combination must be able to stop within the requirements of the Heavy Vehicles Brakes Rule. If the HVEK cannot verify this, the combination cannot be certified.

Because the HVEK certifier is required to include the light vehicle in the brake certification of the trailer and its dedicated combination, so an additional exemption to certify the modifications to the light vehicle must be requested to allow this.

Such a combination becomes a vehicle not of a class in Table A: Vehicle classes (Land Transport Rule: Vehicle Standards Compliance 2002). Some provisions of Land Transport Rules treat the combination while others treat the individual vehicle (eg the mass ratio of VDAM looks at the combination while the provisions of the Heavy Vehicles Rule applying to drawbeams are directed to the towing vehicle and don’t apply to light vehicles).

The provisions of 4.5 of Land Transport Rule: Vehicle Dimension and Mass 2016 apply and the gross mass (Note 1) of the heavy trailer must not be greater than 1.5 times the gross mass of the towing vehicle. Where the gross mass of the towing vehicle is not known, the 1:1.5 loading requirement must be used for guidance and the HVSC must ensure, to the best of their ability, that this requirement is not exceeded. Where the light vehicle manufacturer quotes a GVM or MTM this cannot be ignored.

Whilst the towing connection on the light vehicle doesn’t require certification, the certifier should confirm that the towing connection fitted to the light vehicle has a rating compatible with the heavy trailer being towed.

The certifier must be satisfied that the towing connection:

  • doesn’t place undue strain on the towing vehicle when used as intended, and
  • the combination is safe to operate.
Note 1

Gross mass means the total mass of that vehicle and its load, equipment, and accessories, which may be determined by calculating the sum of the mass on the vehicle’s axles or axle sets.

Page amended 9 April 2018 (see amendment details)

Page updated 26 June 2018 (see details)