NZ Heavy Haulage Association

The category of an overdimension load determines what safety measures are required

Know your oversize load categories

THE SAFETY REQUIREMENTS FOR OVERSIZE LOADS ARE

directly related to the size of the load – a combination of width, forward distance, height, overall length, as well as forward and rear overhang.

The rules for these combinations are primarily determined by the category of the load in the VDAM Rule, but also the overall height and length of the load/vehicle.

There are four different categories that overdimension loads are divided into, and this is primarily based on the combination of load width and the forward distance of the loaded vehicle.

Normally, assessing the width of the load is straightforward – but bear in mind that the trigger widths need to be exceeded to move to the next category. So a load has to be wider than 5.0 metres in order to be regarded as a Category 4 load.

In addition, note that a written permit is required for Category 3 and Cat. 4 loads – and a condition on these permits is that the width of the load has to be within 500mm of the maximum width dimension written on the permit.

However, in most cases, permits do not have the actual dimension noted on there – so there is generally no liberty to exceed the stated dimensions for each category.

The assessment of forward distance can be a more complex calculation, which generally is the distance from the rear axis to the king-pin – but for combination vehicles there may be other factors to take into account. Consult the VDAM Rule or an oversize transport specialist for the details of how this affects the forward distance of an individual load.

The combination of both width and forward distance primarily determines the category of the load, and the graph provided in the VDAM Rule dictates the boundaries where the load steps to the next category.

In addition, the overall length of the load can move the load into the next category. For example, if the overall length exceeds 25m then the load is automatically at least a Cat. 2 load.

The category of the load determines the range of safety measures that are required. This can include: 1. Signage on the vehicle and load – such as the hazard panels and OVERSIZE signs 2. Lighting on the load and the load vehicle 3. Travel restriction times that restrict oversize loads from travelling at peak times 4. Load piloting requirements to provide advance warning to other road users. The Rule contains the mandatory numbers and classes of pilots, which vary depending on the category of load – but the transport operator can elect to provide more load pilots if required for the safety of a load on a particular route.

Another set of factors that can make a difference to the category of a load is its front and rear overhang, and this can push the category of the load to a higher level if, for example, it exceeds 7m rear overhang….or an extra load pilot may be required.

The height of the load doesn’t affect the category of the load, but it does affect what extra permissions and approvals are required from NZTA and overheight asset owners – such as power line owners. Note that if a load is only overheight then there may still be permit and piloting requirements – as specified in the VDAM Rule.

There are many different factors involved in the transport of an oversize load, and for each individual load the dimensions and category of a load determine the conditions for travel, and the safety warning requirements.

Transport operators need to be across all these requirements to ensure that they comply with the rules – and provide the required safety measures to ensure that other road users are kept protected from the risks associated with transporting an oversize load. T&D