The purpose of this webpage is to provide operators with mass limits and access information relating to prime movers or rigid vehicles fitted with a twinsteer axle group.
For information on B-Doubles or Road trains fitted with a twinsteer, refer to the relevant notice.
What is a twinsteer prime mover / rigid vehicle?
Twinsteer is a term given to a hauling that is fitted with a tandem steering axle group.
The tandem steer axle group is fitted with single tyres to both axles and are connected to the same steering column. The axles are spaced at least 1m apart but no more than 2m apart.
Dimensions for a prime movers or rigid vehicle fitted with a twinsteer axle group
A prime mover or rigid vehicle fitted with a twinsteer axle group must comply the prescribed heavy vehicle general dimension in the Heavy Vehicle (Mass Dimension and Loading) National Regulation (MDL Regulation) or operate under a notice or permit. Refer to Table 1
Table 1 Overview of Heavy vehicle prescribed dimensions affecting twinsteer hauling units
|
Measurement |
Maximum dimension |
|
Width |
2.5m |
|
Height |
4.3m |
|
Length |
12.5m |
|
Rear overhang |
3.7m or 60%of the wheelbase (whichever is lesser) |
Mass limits for a prime mover or rigid vehicle fitted with a twinsteer axle group
General mass limits
General Mass Limits (GML) apply to all heavy vehicles. The MDL Regulation provides two GML for a twinsteer axle group, the mass limits are determined based on the fitment of loading sharing suspension. The twinsteer vehicle must not exceed GML unless operating under an exemption under the HVNL (Notice or Permit).
Note: A hauling unit fitted with a twinsteer axle group, may need to operate at a reduce mass when in a combination in order to comply with a total combination mass limit under the MDL Regulations or a Notice.
Load sharing suspension means, an ‘Axle Group’ suspension system that utilises hydraulic, pneumatic, mechanical or other means to effect substantially equal sharing, by all the ground contact surfaces of the ‘Axle Group’, of the total load carried by the ‘Axle Group’ and has effective damping characteristics on all ‘Axles’ of the ‘Axle Group’.
Table 2 GML applicable to a prime mover or rigid vehicle fitted with a twinsteer axle group.
Table 2 Mass limits of a prime mover or rigid vehicle fitted with a twinsteer axle group
|
Twinsteer axle group of a prime mover or rigid vehicle |
Mass (t) |
|
Steer axle |
|
|
Twinsteer axle group without a load-sharing suspension system |
10.0 |
|
Twinsteer axle group with a load-sharing suspension system |
11.0 |
|
Single drive group of a prime mover or rigid vehicle |
Mass (t) |
|
Single axle group fitted with single tyres with section widths of - a. less than 375mm b. at least 375mm but less than 450mm c. at least 450mm |
6.0 6.7 7.0 |
|
Single axle group fitted with dual tyres |
9.0 |
|
Tandem drive group of a prime mover or rigid vehicle |
Mass (t) |
|
Tandem axle group fitted with single tyres with section widths of - a. less than 375mm b. at least 375mm but less than 450mm c. at least 450mm |
11.0 13.0 14.0 |
|
Tandem axle group fitted with single tyres on 1 axle and dual tyres on the other axle |
13.0 |
|
Tandem axle group fitted with dual tyres on both axles |
16.5 |
|
Tri-axle drive group of a prime mover or rigid vehicle |
Mass (t) |
|
Tri-axle group fitted with - a. single tyres with section widths of less than 375mm on all axles b. single tyres with section widths of less than 375mm on some axles and dual tyres on the other axles |
15.0 |
|
Tri-axle group with a. single tyres with section widths of at least 375mm on all axles b. dual tyres on all axles c. single tyres with section widths of at least 375mm on some axles and dual tyres on the other axles |
20.0
|
Axle mass spacing limits
In addition to the axle group mass limits mentioned above, the distance between axle groups determines the maximum allowable mass over those axle groups.
Example 1 Twinsteer maximum mass limit spacing requirement, demonstrates the minimum axle spacing requirements of a prime mover fitted with a twinsteer axle group, required to obtain the maximum GML as mentioned in Table 2 (11t for load sharing)
Axle spacing mass limits means, the distance between axle groups which determines the maximum allowable mass over those axle groups.
Example 1 Twinsteer maximum mass limit spacing requirement
Networks and approved access areas
A prime mover or rigid vehicle fitted with a twinsteer axle group are eligible for general access in participating jurisdictions of the Heavy Vehicle National Law (HVNL). The combination must comply with GML requirement, including axle mass and axle spacing limits .
General access means, these vehicles don’t require a permit or notice to run on the road networks. These vehicles have as-of-right access to the network unless otherwise signposted.
Note: The operators must comply with any other road rules or direction of an Authorised Officer including infrastructure load limits.
Additional resources
Twinsteer prime mover towing a semitrailer