When a vehicle rounds a curve it has a lateral force pushing it to the outside of the curve. This is known as the centrifugal force or lateral 'G'.
This lateral 'G' force increases with sharper corners and increased speed.
HMVs have a higher centre of gravity than a motor car, and therefore in most cases a loaded HMV will roll before their tyres lose traction and slide.
Research has shown that HMV roll overs make up the largest proportion of truck crashes in New Zealand putting a large financial burden on operators, insurance companies and government agencies. They also often claim human lives.
New Zealand has implemented regulations surrounding static rollover thresholds or SRTs, to reduce incidents of HMV roll overs.
SRT is the measure of the roll over force on a HMV. In New Zealand this threshold has been set at a minimum of 0.35 g.
This means that the lateral force acting on a loaded HMV and its load must exceed 0.35 g to roll the unit.
To ensure their stability, heavy vehicles with a gross vehicle mass (GVM) greater than certain specified limits need to meet the minimum SRT value.
If a vehicle doesn’t meet (or exceed) the required stability limit, its stability may be improved by operating it with a reduced load mass and/or reduced load height, or the vehicle can be modified so it has sufficient roll stiffness to operate safely at maximum carrying capacity.
The maximum height and weight of the load is displayed on the vehicles loading certificate affixed to the vehicle.
If you operate a goods service vehicle, there are some important things you have to do to meet the legal requirements in relation to SRT.
LTNZ provides an online SRT calculator so that operators are able to verify that their loaded unit complies.
This information is published by LTNZ to enhance road safety.
We now have adhesive stickers that can be placed on the inside of HMV windscreens reminding drivers of this recomendation. These are free to transport companies throughout New Zealand. Companies need only contact us and pay for postage and packaging in order to recieve them. These have been provided through a safety initative by ACC.
Please contact us for more information on how we can assist you and your clients.
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