---

Past Issues

July 2005

---

With the law limiting axle loads and gross combination masses being more strictly enforced, overloading has been substantially reduced, especially on our main traffic arteries, the N1, N3 and N4 says Fritz Hellberg of Hellberg Transport Management, who, in this article, puts forward the case that it's not too difficult to stay within the law.
 

Staying within the legally allowed gross combination mass (GCM) or the legal gross vehicle mass (GVM) is not all that difficult. One merely has to subtract the tare mass of a vehicle/rig from the GVM/GCM of that vehicle/rig to establish the load that may legally be carried.

Usually the weight of the load to be carried is also known - by pallet weights, material densities or other means - and by the simple arithmetic of comparing the proposed load with the legal payload, the legality, or otherwise, of the loaded vehicle can be ascertained. 

The difficulty is knowing exactly where to place the load to avoid individual axles or axle-groups being overloaded. With unsymmetrical and varying-density loads (such as sugar cane, timber or fabricated steel), this is extremely difficult. Loading these products effectively so no permissible mass limits are exceeded can only be achieved by weighing individual axles/axle-groups of the loaded vehicle/rig and shifting the load till the weights are right, or by having on-board weighing equipment that gives the information instantaneously.
 

In this 6X4-interlink combination, the GCM is close to the maximum allowed overload limit of 5% yet all the axle groups are below the legal limit, one even being 2.5 tons under.

The former is time consuming and the latter can mean a capital investment in excess of R100 000 which may be difficult to justify in some circumstances. 

For items of known weight and dimension there is another way. The exact position where the load should be placed can be calculated. A calculator and an operator who knows the formulae of bending moment calculations (a geometric calculation to determine proper load distribution on a rig) could ensure correct load distribution but the margins for error are always present under these circumstances. 

An alternative is to use a reputable computerised Load Distribution programme. With such a programme, the vehicle/rig can be pre-loaded theoretically and the printout it generates can provide exact detail of load placement to the driver or loading foreman. 

It must also be borne in mind that some rigs are more sensitive to axle overloading than others. In the case of a 6X4 truck-tractor pulling a set of interlink trailers, the sum of the legal permissible axle loads exceeds the legal GCM of 56 tons by as much as 5.5 tons. This means that some axle groups might be as much as 3 tons below their legal weight limit when the legal GCM has been reached. This in turn means that the exact placing of the load is not all that critical and can be as much as 1.5 metres away from the ideal position without causing any axle overloads.

Paul Collings Comments: While what Mr Hellberg has to say is indeed enlightening, transport operations are characterised by fast-moving, hands-on procedures and more importantly in this instance, skills shortages. As a result, technology-driven solutions for effective/legal loading could be seen as 'pie-in-the-sky' ideals under current circumstances. However, loading bulk cargo like sand and coal without the aid of technically clued up staff and load measuring technologies is a very tricky business. Judging by what the KZN provincial overloading report shows, even those operators with 'best practice' policies, procedures, skills and technologies in place are still falling foul of the law. Technology is an enabler but it needs to interface effectively with people, not just the managers at the transport office, but the drivers of both truck and loading vehicle as well. Once again it's about skills development, probably the most important issue facing the transport industry right now.
 

The 4X2-tridem semi combination is 780 kg under the maximum legal GVM of 40 500 kg and yet the least-loaded axle (steering axle) is only 620 kg under the legal limit. The trailer used in this rig has the trailer bogie moved too far back for a 4X2 truck-tractor and therefore the load had to be moved 1.36 metres back from the centre of the loading area to achieve legal axle loads.