Current projects / Twin steer and tri-drive operations (policy work complete)

Exploring ways to improve productivity by revising the mass limits for heavy vehicles fitted with twin steer and tri-drive axle groups

Twin steer and tri-drive operations (policy work complete)

  • Scoping > 
  • Analysing issues > 
  • Analysing options > 
  • Implementing

Purpose

This project aims to unlock significant productivity gains from heavy vehicles utilising twin-steer and tri-axle groups in order to meet the demands of Australia's increasing freight task.

Currently, the mass limits under the heavy vehicle national law relating to heavy vehicles using twin-steer and tri-drive axle groups do not allow for the vehicles to be used to their full payload capacity.

In consultation with stakeholders, we are working on two separate but related proposals to increase the current allowable mass of:

  1.      twinsteer axle prime movers towing a semitrailer
  2.      tri-drive prime movers towing a semitrailer.

Next steps

The NTC recommended allowing twin-steer prime movers towing a semitrailer to operate with a mass limit of 46.5 tonnes at GML and 49.5 tonnes at HML.

The axle mass limit for a twin-steer axle group that is not fitted with a load sharing suspension system will remain at 10 tonnes.

The axle mass limit for a twin-steer axle group with a load sharing suspension system will be 11 tonnes. This increase will be achieved by amending the Heavy Vehicle (Mass, Dimension and Loading) National Regulation 2013 (the regulations) as part of the HVNL maintenance package to be considered by ministers in 2017.

The NTC also recommended that existing regulations governing the allowable mass limits for tri-drive prime movers towing a semi-trailer should be retained.

Background

This project stems from a 2013 Transport and Infrastructure Council directive that asked the NTC to explore ways to encourage the wider use of twin-steer and tri-drive axle groups.

A prime mover is a heavy motor vehicle designed to tow a semitrailer. Twinsteer means a group of two axles (with single tyres) in the steer axle group connected to the same steering mechanism fitted to a motor vehicle.

A tri drive is a motor vehicle incorporating three axles in the drive axle group; the drive forces may be transmitted through two of the axles or all three axles, in either equal or unequal torque-sharing configurations.

General mass limits determine the maximum weight an axle group or heavy vehicle combination can carry to gain access to the general road network. Higher mass limits are available to operators in a restricted road network under a special permit or notice.

Get involved

Reports open for comment

Contact us

Project Manager Melissa O'Brien
Last Updated: 8/3/2017