What is the rear overhang?
A vehicle’s rear overhang is the distance between the vehicle’s rear and its rear overhang line.
Where is my rear overhang line?
- If a vehicle’s rear axle group has only 1 axle, the rear overhang line is the centreline of that axle.
- If a vehicle’s rear axle group has 2 axles and 1 has twice the number of tyres as the other, the rear overhang line is one-third of the distance between the 2 axles and closer to the axle with most tyres.
- If a vehicle’s rear axle group has a steerable axle, you can’t count that axle unless:
- the group has only 1 axle, which is a steerable axle; or
- all the axles in the group are steerable axles.
- For other axle groups – for example, when all axles are fitted with the same number of tyres – the rear overhang line is the centreline of the axle group.
Rear overhang limits
The pictures in this section are just examples. As discussed above, vehicles have different axle and tyre configurations, which determine the location of the rear overhang line.
Rear overhang on rigid trucks – Lesser of 3.7m or 60% of wheelbase
Rear overhang on semitrailers and dog trailers – Lesser of 3.7m or 60% of ‘S’ dimension
The ‘S’ dimension is the distance between the trailer's front articulation point and its rear overhang line
Rear overhang on a pig trailer – The rear overhang on a pig trailer must not exceed, the lesser of the length of the load-carrying area forward of the rear overhang line and 3.7m
Rear overhang on other vehicles, such as a bus – Lesser of 3.7m or 60% of the wheelbase
For vehicles fitted with retractable axles, rear overhang requirements must be met in retracted and unretracted positions.
The Heavy Vehicle Network Access Policy determined that a rigid towing vehicle fitted with a flat-bed tilt tray body, which is towing a vehicle via its rear-mounted wheel lift, is considered a heavy vehicle combination for the purposes of assessing dimensional compliance.
Hence, the vehicle being towed is regarded as a ‘vehicle’, rather than a ‘load’, when its front/rear wheels are secured in the wheel lift, and the other wheels are in contact with the road (either directly or via lifting dollies, in cases where the wheels are inoperable). This means that the applicable length limit for that combination is 19 metres, not 12.5 metres.
The rear overhang limit for rigid vehicles does not apply to the rear-mounted wheel lift when being used to tow, as in that configuration, the structure of the lifting device is regarded as a drawbar.
In all instances, the towing vehicle and the towed vehicle must comply with all other relevant Heavy Vehicle National Laws, requirements for towing, and any other applicable regulations.
Measuring your rear overhang
The following pictures show where you should measure your rear overhang, based on different axle groups and number of tyres. They are just examples, and other variations may apply.
Example | Axle type | Rear overhang |
---|---|---|
4-axle low loader ![]() |
Last axle is steerable |
Centre of second axle to rear of table |
6-axle platform trailer ![]() |
All steerable |
Centre of axle group |
3-axle controlled access bus ![]() |
Last axle is steerable |
Centre of first axle in rear axle group |
3-axle controlled access bus![]() |
Rear axle group where the
|
1/3 of axle spacing closer to the axle with 4 tyres |
3-axle truck and 4-axle dog trailer![]() |
Rear axle group fitted with dual tyres on each axle |
Centre of last axle group |
Rear overhang exemptions
Some notices and permits exempt a vehicle from the length requirement for rear overhang in the MDL Regulation. If you are operating under one of the follow notices, there may be additional rear overhang allowances available.
- National Class 1 Load Carrying Vehicle Dimension Exemption Notice 2024 (No.2)
- National Class 1 Agricultural Vehicle and Combination Mass and Dimension Exemption Notice 2024 (No.1)
- National Class 2 Bus Authorisation Notice 2024 (No.1)
- National Class 3 Bus Rear Overhang Dimension Exemption Notice 2024 (No.1)
- National Class 3 Rear Overhang Dimension Exemption Notice 2024 (No.2)
Notices can be viewed and downloaded from the NHVR national notices page.