Sensible Axle Loading

Remain Vigilant

One day, here in Australia, we may get to some sensible axle loading regulations, but the political wrangling between states’ road managers and the regulators means it isn’t going to happen anytime soon. It is always the same, rationality goes out of the window when it comes to stuff like axle weights and road and bridge capabilities.


These thoughts were provoked by a post put up by someone showing the rather ridiculous rules around twin steer prime movers. Twin steers are never going to be viable in the current mass regime as this, inherently more stable, prime mover gets punished with lower payload and, hence, lower productivity.


The question is an innocent one, but should be asked on a regular basis. If I put an extra steering axle on the road, and the truck meets all of the dimension and axle loading requirements, why can’t I get a higher mass limit than the single steer truck?


The numbers are clear, as are the regulations. Certain axle spacings and dimensions are deemed to protect the highways from damage, but not in the case of a twin steer. Running with the extra prescribed mass on a second steer axle is seen by the rules as unacceptable.


Some operators have found a solution to this issue, by going down the Performance Based Standards route. A little bit of extra length with get you over the line in this case. However, the prime mover is limited in the way it can be used and reduces flexibility in a fleet. It can only run with a specific trailer and if it pulls another trailer, it is penalised, losing the mass of the extra axle in payload.


This is not the first time the issue has come up. In fact, there was a lot of work done in this area over ten years ago. A discussion paper was produced in 2004 for VicRoads, then a draft proposal and regulatory impact statement appeared in both 2006 and 2007.


The premise was simple, with two scenarios plotted out. One assumed the mass allowed on a pair of twin steering axles remained at 11 tonnes and the second assumed an increase up to 11.5 tonnes on the axle pair. Let us not forget, if these axles are fitted on their own, as a single steer, they are deemed capable of handling 6.5 tonnes, considerably more than 50 per cent of 11 tonnes.


If we assume all of the rules we have today remain the same, with axle loading as it is today, but with overall GCM calculated from the sum of all the axle limits, we get some interesting results. All of a sudden a GCM of 42.5 tonnes for a semi can become 47.5 tonnes. It gets better, if the truck works under Higher Mass Limits the GCM goes up to 50.5 tonnes. It gets even better if you allow a, reasonable, 11.5 tonnes on the twin steers, up to 51 tonnes.


With all of the dimensional rules the same, the bridge loading calculations should also accept this as a reasonable ask. This is especially the case, if we calculate the sum total of overall road wear per 1,000 tonnes of freight and not for each individual truck. After all, if the payload goes up the number of trucks goes down.


Then we can extend the calculations to B-doubles. We need to, because we need the prime mover to be interchangeable between semis and B-doubles. 67.5 tonnes for a standard set-up, with 73 tonnes GCM under HML, plus another 500 kg, up to 73.5 tonnes GCM with a 11.5 tonnes twin steer allowance.


What happened to this eminently sensible proposal? It got lost in the fog of war. The war between state and federal regulators, between departments within the same governments and between government agencies and the authorities they are trying to help.


Perhaps the regulatory situation is a little more rational these days? Perhaps a bit of the fog has cleared and perhaps someone could dust off these old reports and give them a second look?