Since permitting for the nine-axle 50MAX vehicles was introduced in late 2013, more than 600 vehicle combinations have received the stamp of approval says the New Zealand Transport Agency.
With new applications rising steadily, and more and more districts opening up to 50MAX, NZTA says it appears to be only a matter of time before 50MAX will become the new heavy truck of choice.
NZTA’s principal structural engineer John Reynolds says the seeds for the growth of 50MAX were planted with the introduction of the new high productivity motor vehicle (HPMV) at the beginning of the decade. These newer and larger trucks came into being following an amendment to the Land Transport Rule: Vehicle Dimensions and Mass (VDM Rule) in 2010. This allowed for changes to the lengths for heavy vehicles and also creating a new high productivity permit class for vehicle combinations at increased weights.
“HPMVs were bound to certain routes – basically over those roads and bridges that could handle the new sizes,” says Reynolds. “The bottlenecks were mainly at bridges – a lot of our bridges were simply not suitable to carry HPMVs.”
A nationwide screening programme revealed that older bridges in particular were not suitable for the heavier weights.
“That’s when we started looking at having ‘limited’ HPMVs, vehicles that would be heavier than conventional 44 tonne trucks but not so heavy that they couldn’t be driven over our bridges.”
What happened next was a simple mathematical exercise. As most older bridges have relatively short spans (16 metres or less), it was not the total weight of the truck that mattered, but only how much weight would be concentrated on a bridge span at a time.
“We worked out that, if a vehicle was 20 metres long, you could go up to 50 tonnes total weight with very little effect on bridges – a massive gain for any transport operator.”
The secret was adding an extra axle to the truck to spread the weight load says NZTA national network optimisation manager Graham Taylor.
“It’s quite simple, really – the wear and tear on the pavement is determined by the weight each axle puts on the road, not the total weight of a truck,” says Taylor.
“So if a truck has nine axles, instead of the traditional eight, it can weigh up to 50 tonnes, without creating any additional wear and tear on the road pavement.”
“The main beneficiaries are local communities,” says Taylor “Full HPMVs can really only travel on 5% of the national network. But because 50MAX is effectively impact-neutral on bridges and roads, it opens up 90% of roads to higher payloads, bringing freight transport costs to and from communities in New Zealand’s heartlands down considerably.”
Taylor says a business case study has put savings in annual freight transport costs at $100 million by year four.
“Add to that the same high safety standards that are required of other HPMVs (including increased resistance to roll over and the inclusion of electronic braking systems), and suddenly you’ve got a truck that is not only more efficient, but also safer,” he says.
“A number of operators are investing in even more safety measures, such as speed limiting, GPS monitoring, weight load cells and electronic stability control.
“These features are additional benefits 50MAX will deliver to improved road safety through the reduction in truck trips needed to move the same amount of freight.”
Fact Box – 50MAX
· Are a combination weighing up to 50 tonnes
· Have one more axle (nine, or ten for B trains) than conventional 44 tonne truck combinations
· Have higher safety requirements than conventional 44 tonne trucks (such as electronic braking system, increased roll-over resistance)
· Cost-neutral in relation to on-going impacts on pavements and structures (roads and bridges)
· Need a special permit
· Pre-defined design criteria for truck and trailer combinations allow permits to be issued quickly
· First permit issued in October 2013
· 600+ permits issued at March 2014
