Trucks and heavy vehicles are a key part of our economy. They literally shift massive cargo from coast to coast, and this often involves drivers being on the road for hours at a time. Sometimes, these trucks can cause lethal accidents that are aggravated by three main factors:
- The speed of the truck affects safe breaking distance.
- The weight of the truck causes greater impact.
- Driver fatigue slows response time.
Each of these factors can be addressed separately to enhance road safety, and various regulations have been put in place to prevent accidents. HVNL (Heavy Vehicle National Law) on heavy loads are among the most important of these, and the easiest to implement. They vary depending on the type of cargo being handled by your truck.
Agricultural vehicles include field bins, augers, harvester fronts, conveyors, and irrigating equipment or machinery. Trailers and trucks carrying agricultural materials are also grouped here. Trailers fall under Class 1 heavy restricted access vehicles, while other agricultural vehicles are only considered Class 1 if they stretch outside stipulated weight rules.
Safety regulations cover the weight and dimensions allowed for your truck, so if you need to exceed them in any way, you’d have to apply for a Mass or Dimension Exemption Permit from the National Heavy Vehicle Regulator (NHVR). The permit lasts 3 to 5 years.
Vehicles being used for agricultural purposes require warning lights that have the following features:
- Rotating yellow non-strobe light that flashes 120 to 200 times a minute
- Powered by 25W LED or 55W regular bulbs
- Be visible from 500m in every direction
- Have a supplementary light in case the main one fails
- Have a filter to dim the driver’s view of the light and prevent distraction
Other warning features include fluorescent yellow paint on axle parts that stretch more than 150mm outside the vehicle tyres. You can also wrap the extension in fluorescent yellow and/or highly visible material. At the back and sides of the vehicle, there should be a warning sign that has 150mm diagonal stripes in black and white or red and white. The stripes can be wider, and the whole sign must be at least 0.16m2.
If your agricultural vehicle is oversize, it needs a bright yellow reflective sign that says OVERSIZE. It has to be zincalume or aluminium and have black lettering and a black border. It has to be horizontally positioned 500mm above the ground, and must be at least 1200mm by 450mm, allowing 200mm by 125mm border around the text for better legibility.
Mass limits for heavy vehicles
They are three main classes of weight stipulations for trucks. These are General Mass Limits (GML), Higher Mass Limits (HML), and Concession Mass Limits (CML). For all vehicles that contain and carry large loads, regular maintenance and servicing is essential. This includes oil checks, and engine inspection. Drivers and fleet managers should be sure to use safe, reliable, compliant truck parts, preferably parts that are within the vehicle warranty.
Under HVNL, trucks are required to be 2.5m wide and 4.3m high. Trailers carrying livestock or two decks of cars can extend to 4.6m, while double decker buses must never exceed 4.4m. Trailer length ranges between 9m and 13m depending on cargo. The rear overhang is 3.7m. B-double livestock trailers must not exceed 18.8 metres of the total combined trailer.
Standard weight limits for heavy vehicles are 42.5 tonnes for GML with a maximum concession of 43.5 tonnes and a HML of 45.5 tonnes. Concessions (CML) have to be approved by National Heavy Vehicle Accreditation Services (NHVAS), and higher mass limits (HML) need specialised shocks and/or suspension approved by NHVAS.
Trucks that have additional trailers can range from 19m to 53.5m, depending on the number of trailers in the chain. B-double trailers can go up to 50 tonnes general access and 55.5 tonnes restricted access. CML and HML can carry an additional 1.5 tonnes.
The longest road-worthy configuration is a BAB Quad Road Train that has four trailers attached, 16 wheels, and a combined length of 53.5m. This type of heavy vehicle can carry 119 tonnes under GML, 121 tonnes CML, and 130 tonnes HML.
Mass distribution along the train depends on the number of wheels per axle group. Dual axles can carry 16.5 to 17 tonnes a pair, while triple wheel groups can carry 20 to 22.5 tonnes a set. This balanced weight distribution helps keep the truck stable and avoid tipping.
Trucks regularly pass through weigh stations along their routes to maintain these mass-based safety standards. Compliance fines are heavy but valid, because the potential loss of life from such heavy, speeding trucks can be lethal to other road users.