Despite fairly overwhelming opposition, it has been decided to allow the maximum weight of trucks on New Zealand’s roads to increase from 44 tonnes to 53 tonnes – although only on particular routes designated for this increase. Supposedly this increase will lead to the more efficient shifting of freight around New Zealand. This is what the government says anyway:

“Developing this permit system creates an environment where productivity gains in the range of 10 to 20 percent could be realised by using fewer trucks to carry a given amount of freight while enabling the impacts of heavy vehicles to be properly managed.

“This will help to reduce road congestion, operating costs, vehicle emissions and improve the road safety environment by slowing the increase in heavy vehicle movements on New Zealand’s roads.”

Trucks carrying heavier loads will not be any wider or higher than present vehicles, though a limited number may be slightly longer. Roads that are allowed to be used by vehicles will be specified in their permit and road controlling authorities will have the final say on whether routes applied for are suitable for heavier vehicles.

Any vehicle issued with a permit to operate at a heavier weight under a permit system will have to meet all appropriate safety requirements.

I must say I would be rather surprised if that result of this change was  seeing 10 to 20 percent fewer trucks on the road, although it seems as though that’s not quite what’s being promised here. It seems a bit more likely that this change enables trucks to compete with rail for bulk, heavy freight – which is a rather odd move by a government that actually owns the rail system.

Both the Labour Party and the Green Party have strongly critiqued the change. This extract from the Green Party’s media release is, I think, particularly important:

Hundreds of thousands of journeys in 53 tonne trucks will exponentially increase the damage to our roads. Increased RUC (Road User Charges) will not cover the increased costs of damage done to local roads. Neither will they cover the upgrading of hundreds of bridges in our road network to accommodate the increased loads.

“Most of the claimed productivity gains simply reflect the shifting of costs from trucking companies onto ratepayers,” said Mr Hughes.

“For example, benefit cost calculations for this decision were made on the assumption of an additional $150 million needed over 10 years for bridge upgrades. The actual cost of bridge upgrades could easily approach $380 million according to the Ministry of Transport’s own analysis. Trucking companies will not be paying for these additional costs. Motorists and ratepayers will.”

The economics of this issue are quite interesting really. The damage done to roads is not directly equivalent to the extra weight of a vehicle on it, but rather equates to what is known as the “Fourth Power Rule“. As the weight on the road from each axle of a truck increases, the amount of damage done to the road increases by the fourth power. This means that a 20% increase in axle weight results in more than double the road damage.

53 tonne trucks may well have more axles than 44 tonne trucks, but if they didn’t my calculation is that they would do roughly double the road damage. It appears somewhat unlikely that these heavier trucks will have to pay twice the road-user charge than the current 44 tonne trucks. If they do pay twice the amount, then I wouldn’t nearly have as much of an issue with this change.

The other issue is “who pays for the increased road damage?” Unless the heavier trucks are totally restricted to state highways, it will be ratepayers who end up picking up around 50% of the tab for this additional damage. So even if RUCs increased to fully compensate for the damage these larger trucks are doing, they would actually only compensate 50% for non-state highways.  What makes this particularly interesting is that councils are the ones who own and control local roads (except, in the future in Auckland it will be the Steven Joyce appointed Auckland Transport Agency who do it). This means that they have the ability to say “no” to these heavier trucks. Because the larger trucks will be doing twice the damage to their local roads, and because the level of compensation councils will get from the increased RUCs (if they’re increased enough) will still not cover the increased cost to council, I would not be surprised if all councils basically did say “no”. I mean, why on earth wouldn’t they?

Which means that the whole thing is a bit pointless. I doubt that particularly many trucking trips can take place without any travel on local roads – particularly in Auckland where the state highways are usually motorways. I must say I will be rather amused if all the councils say “no” to the larger trucks.

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  1. As you’ve pointed out, Auckland Transport will be Joyce/Hide controlled anyway for its first three years, and they will likely issue permits. Therefore I believe Auckland will see these 53 tonne trucks unfortunately.

    This will increase the pressure on other councils to follow suit. “See? Auckland doesn’t have a problem with heavier trucks…”

    I hope I’m wrong.

  2. The Greens and Labour wouldn’t be too pleased with road trains, it seems. The largest of these top out at around 200 tonnes, altho 120 tonnes is more typical. They used to roll past my apartment in northern Australia. It was never a lot of fun passing one on a dirt road, but you could tuck yourself in behind one at night and you’d be safe against cattle, kangaroos, and all the other wildlife that makes driving at night in Outback Australia so hazardous.

    “which is a rather odd move by a government that actually owns the rail system”

    That’s a good argument for the government NOT owning the rail system. In the bad old days pre-1984, the government regulated to favour its own trading interests rather than the country or the economy as a whole. So it was illegal to send goods further than 150km (150 miles?) using a method other than rail. Sea freight is much more efficient (in terms of cost and environmentally) than rail for bulk goods, and usually road freight is more efficient for just-in-time inventory management. I recall goods were often “exported” to Australia and then immediately re-imported to another NZ city by sea freight because it was still cheaper than using the railways.

  3. Oh, and… Could someone explain the fourth power rule to me? Why isn’t the increase in damage proportional to weight per axle?

    1. Damage is related to energy transfer to the road surface, not just the deflection due to weight. A lot of things in engineering don’t follow “intuitive” expectations. Anyway, the argument is a bit specious: the issue is axle loading, not gross vehicle weight. In Australia and N.Z. the weight specifications ensure that the vast majority of truck and semi-trailers use dual tyresets on the load axles. In the U.K. the road tax regulations force truck owners to use single-tyre axles on heavily-loaded vehicles, leading to a lot of truck crashes on the motorways: a blowout almost always leads to a closed motorway, as the trucks jacknife and crash. Typical is 2+4 for the tractor and 2+2+2 on the semi-trailer = 12-wheeler: N.Z. is usually minimum 2+4+4 tractor, 4+4+4 trailer = 22-wheeler, like Australia, and for the petrol tankers 2+2+4+4+4 tractor and 4+4+4+4 trailer! Road trains are really big, but the axle loads are quite low. otherwise they would be unusable on outback roads.

  4. Obi, I don’t know the details of the mathematics behind it, but I think it’s to do with how asphalt responds to heavy loads being put on it. When a truck drive along a road the asphalt actually lifts up ahead of each wheel (obviously only very slightly). Perhaps as extra weight is added, it becomes very much increasingly difficult for the surface to recover from that.

    The road trains in Australia are very very long though aren’t they? The key here is weight per axle.

  5. Looking forward to the Newmarket overbridge not being able to cope with a traffic jam of 53 tonne trucks in both directions. And let’s hope (for John Banks’s sake) the Mayor of Newmarket isn’t walking under the bridge when it when it collapses under that weight.

  6. Obi, I think that the 4th power rule comes mainly from observation and experiment — watching how a road surface responds to different loads then finding a best fit line — rather than having a strong theoretical basis. As such, it is only a heuristic that applies to certain conditions.

  7. Thanks Admin and David for your 4th power comments. It strikes me that if the road is built properly (ie. not a thin layer of tarseal over compacted dirt, like most state highways in NZ) then damage by normal trucks will be tiny, and damage by slightly bigger trucks to the power of 4 will therefore still be tiny. If, as Admin says, the road surface is lifting and flexing (which seems like a good explanation), then this isn’t going to happen much at all with a thick road surface.

    I believe that motorways are fairly substantial in their construction. I vaguely recall an article I read many years ago contrasting European and US motorway construction “recipes”. The Europeans specified required performance and longevity, left the construction companies to it, and ended up with innovative motorway surfaces consisting of layers of all sorts of modern materials. The US, on the other hand, tended to specify exactly how the road was to be constructed and ended up with roads built to the same specifications as were used in the 1970s, and these had shorter lifespans and required more maintenance. The dodgy concrete slabs you see all over the States being a good example. I’d be kind of curious to know how we do this in NZ. What layers and materials will be used for Waterview, for instance?

  8. “If, as Admin says, the road surface is lifting and flexing (which seems like a good explanation), then this isn’t going to happen much at all with a thick road surface.”

    Obi, the 4th power rule was taught to us back in Germany in calculating on how to construct NEW roads. And Germans, if I am allowed to say so, wrote the book on highways. I admit it is a bit counter-intuitive. But it is a fact observed and studied very exhaustively.

    Also, even if the roads WERE built able to take 53 tons, they AREN’T. Roads ALWAYS flex, because bitumen is a flexible substance, and part of its advantage is that it does just that, rather than resist the loads by brute strength. Concrete generally doesn’t flex, but how many roads are built of concrete? Exactly – pretty much none, because concrete construction is much more expensive.

    So the argument that you could build roads that way (stronger) is pretty useless. You can build something strong enough to pretty much outlast everything you can throw at it, but the costs of doing so are exponentially higher than building a normal road to pre-53 ton standards. Law of diminishing returns.

    This whole thing is just another case of locking us into a road-centric future. Because soon, the damage will start to happen, and then more and more money will have to be set aside to fix it. Then we will be told “Yeah, we would like to spend more on PT and on rail freight – but see, maintenance alone is eating up all our money…”

  9. The best thing, by the way, would be to limit axle weights, rather than total weights. I am unsure the current change does that, and I am not expecting it to. It would be too simple and good. Sure, trucks can have 100 tons load for all I care, if the truck has six axles in back and two in front…

    1. Best practice is electro-pneumatic brakes with antilock: they act faster, and don’t just skid. Fewer trucks is bound to be safer, just so long as axle loads are kept down.

  10. Well the question is, are minimum deceleration values assumed for all trucks (not sure about NZ road code / laws on this one) – i.e. that define how quickly it comes to a stop? If that is the case, and they are the same or better for such heavier trucks, I do not see an automatic safety issue.

  11. Jarbs – As Max says though, if there was a requirement on how fast a truck has to be able to stop then it makes no difference. If they are carrying a heavier load they need to have better brakes, this may cost more to implement but that becomes the cost of carrying a heavier load.

    Max – limiting axle loads sounds like a simple solution to all of this, as you point out it could never be implemented as it is to simple. Bureaucrats like things to be complicated to keep themselves in a job.

  12. I realise that Matt, my question though is if something goes wrong (like it does sometimes) then a 100 tonne truck is going to do more damage than a 44 tonne or a 53 tonne truck.

  13. “A truck driver has been charged over the death of a tourist who was hit by a truck as she cycled around New Zealand.

    Mia Susanne Pusch died in January after being hit on State Highway Three near Bulls. The 19-year-old had been cycling around the country since her arrival from Germany early last October.

    Police have charged a 66 year-old truck driver from Whanganui with careless driving causing death. He will appear at the District Court in Marton next month.”

  14. The accidents cited really have no bearing on this case, since they are of the old truck wights anyway, and any individual incident has individual reasons for it happening. As I noted before, the road damage issue will likely leave us with more lasting (literally) effects…

  15. Roads are designed to take a number of axle passes. Each time an axle passes over a road surface, the road deflects. Most of the deflection is elastic, which means it is recovered. There will be a small amount of plastic deformation each time as well however, which will eventually add up to significant deformation/rutting.

    The amount of plastic deformation for each pass is related to weight by the 4th power rule. This rule has been established by empirical analysis – There are labs where a wheel is mounted to a machine that runs it back and forth across a pavement at a certain pressure continuously…

    A typical motorway pavement might be designed for 30 years, or XX No. of standard axle passes, but there is usually a fair bit of deliberation as to optimising the pavement design for ‘whole of life’ costs.

  16. Trucks will gain a axle or 2 & therefore the weight per axle will be the same as present rules. This will have the same damage to roads & trucks will have the same braking capacity. It will take over 10 years for these trucks to become common place as old trucks are slowly replaced with new, more efficent ones set up for the new rules. It will reduce the trucks on the road, or atleast slow the rate of extra trucks on the road. Trucks cost over $500,000 to put on the road, so transport companys dont want to buy any more than required to get the job done. If 3000 tonne of freight needs to be shifted on the old rules this will take about 100 loads, with the new rules it will take about 83 trucks, 17 less doing damage & clogging up the roads, with about the same number of axles on the road in total.

  17. I’m a bit skeptical about the idea that this will reduce the number of trucks on the road. To me that seems the same kind of argument as “adding this extra lane will fix congestion”. True, initially the number of trucks might not grow as fast but in the longer run we will end up with a lot of trucks on our roads – just instead of being 44 tonnes they’ll be 53 tonnes.

    If they add an extra axle or two to distribute the weight and not cause extra road damage I will of course have less of an issue with the proposal.

  18. Hi, along with the fourth power rule for axle weights, there is also a seventh-power rule for road thickness – that if you increase the road thickness by ten percent, you will double its strength (1.1^7 = 2, more or less)

    So, the problem of a 53 tonne truck (or more precisely, extra weight at the axle – that is what the system is calibrated on) won’t be on the State Highway network – but when those trucks run on rural roads. THEN you will see the effects.

    1. Rural roads are usually designed to take the heaviest vehicle for normal use: cattle truck or milk truck. Which is why they seem to last forever, as there is so little traffic on them.

      1. Except for the rural roads which form the rat-run bypassing the SH1 Bulls weigh station!
        There were articles in the Evening Standard some time ago about the back roads being pounded to pieces by heavy trucks while the weigh station was open.

        1. Having to go in to a weigh-station is punishment in itself. The lost time can put a driver outside his time allowance, and let’s face it, the schedules don’t have any slack! And that’s even if there’s no problem with the weight…

  19. There are no law changes in the weight per axle, just the gross weight.
    At present a truck with 6 axles can go to 43 tonnes, but there are not many on the road as the road user cost too much.
    It is cheaper to run 7 or 8 axles beacuse of the RUC savings. (its calculeted on weight per axle)
    The 53 tonne trucks will, at a minimum run 8 axles, but most will need to have 9, or even 10.
    A typical set up now runs 8 axles at 44,500 tonnes – 5.56t per axle. The same equivalent under the new rules will have 10 axles – 5.3t per axle or 5.9t/axle on 9 axles.
    The maximum legal loadings per axle are 8.2 tonnes on dual tyres & 6 on a single tyred axle, so i dont think road wear will be a major problem.

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