And by how much does it increase stopping time? Without that drag, they will roll further.

I taught my kids: don't drive in front of a truck, especially on a downhill, because they can't stop as fast you and will run right over the top of any car. Now we have to worry about this even more.

I'm surprised that it takes that much calculation. There are a lot of variables you can't control, like the direction of the wind and the presence of junk on the road, that it seems to me that the error bars are bigger than the precision of the computation.

I'd have thought that you could get get, say, half the benefit with an approximation that would take far, far less work. And in actual circumstances, you may find that the optimal solution isn't really any better. Under some circumstances, it may actually be worse.

I imagine they put in all that math trying to control the uncontrollable, and have proven that, say, a 30 MPH side wind isn't going to make it so unstable it flips the thing over.

"Such vehicles are called articulated lorries in Britain, although these tend to be a bit puny compared with American rigs weighing 32,000kg (70,000lbs) or more."

Incorrect. UK trucks go up to 44,000kg. American rigs are actually quite primitive compared to their European counterparts. Euro trucks have far more sophisticated wind kits and have done for quite some time, most US trucks do not. Furthermore, US trucks are not required to have any under-run protection (crash bars) to prevent motorists being decapitated in side impacts, European trucks must have it. Tri-axle trailers which spread the load out and do less damage to the road are ubiquitous in Europe but unheard of in America where the tax-structure has not been put in place to incentivise their use. The build quality of American trucks also leaves a lot to be desired.

Jomiku, I couldn't see this making a huge difference to stopping distances. When you're slowing down, wind resistance becomes less of a factor the slower you get. The weight of the load would be a much bigger factor in how much energy has to be absorbed by the brakes. Fuel savings from better aerodynamics are something that are accumulated gradually over time.

Eamonnca -

While I certainly wouldn't argue that tractor-trailers in the EU tend to be more sophisticated, I would say that the *average* size over here in the US is a lot larger. We also have local variations that allow trucks to go to 147,000lbs. with multiple trailers. (And this doesn't even get into the maximum overload steel trucks you see in places like Michigan, where they have so many axles on the trailer that you wonder how it can possibly turn.)

Moreover, the primitiveness of your average American trailer means that there is *great* potential for improvements made to existing hardware. If this device cuts fuel costs as dramatically as they say and it does not suffer from, say, durability issues, I expect we'll see fairly widespread adoption on fleet trailers.

Is that a lot? Road trains in Australia go to 200 tonnes (440,000 lb). See them all the time in the Northern Territory.

I doubt they're very fuel-efficient, though.

If only there could be an improvement in the road bullies abilities behind the wheel.
How they can drive 15-20mph over the speed limit while tailgating and bullying other traffic to achieve it is beyond me.

And why can't these rigs be given enough power to go up even small grades without losing speed causing tailbacks and bunching of traffic?

@ Eamonnca1 : I think when the Economist refers to the truck lengths, they meant the standard single truck trailer combination, in which case the European trucks are puny. When you speak of the 44 ton truck of the UK, you are referring to the double trailer trucks that are limited to, I believe, 18.75m (or 61ft). The EU actually has an allowance for a longer and heavier truck of 60 tons and 25.25m (82.8ft).

Well, then why not compare to the USA and Canada's double trailer trucks, known as the Turnpike Double. These trucks have 2 x 53ft trailers in a row... a staggering 106ft length ....and the drive horse is an additional 24ft - a total of 130ft ... and a staggering 123tons. I see these trucks on our main highways on a regular basis and they are in some cases spooky to watch.

Tri-axle trailers are no impressive invention but they do have serious issues when a truck turns, excessive wear on the tyres and a higher risk of blowout. The US and Canada allows for drop axles to spread the load and in essence do the same as the tri axle. Drop axles have draw backs too, often the driver raises the the drop axle to do a sharp bend (save the tyres) but then axle loading is too sharp and we find premature road deterioration particularly at bends. I should at this stage let you know that the design load of roads in North America is higher than Europe particularly to deal with this monstrous truck loads.

As for the side protection bars - well considering the number of trucks on the road in North America and the number of side on accidents (let alone decapitation) are so rare, it would be an unreasonable increase in weight. If you really want safe trucks then there are many more features available including skid sheets that even the most safety conscious regulators will agree that it is too heavy and costly.

Australia on the other hand has train trucks which are quite impressive, but secluded to relatively low trafficked interstate highways, as they would be way too dangerous on highways seen in places like North America.

As a last note, apparently "Peterbilt" trucks are notorious for the problems they give, but you don't find many Volvo and Mercedes trucks in North America to compare against Peterbilt, note that Volvo and Mercedes do build cars in North America.

If you look at a map of the USA you will notice that there are quite a few direct East-West and North-South highways crisscrossing the land. These highways are design purely with trucks in mind.

In fact there are way more trucks in North America than in Europe and these trucks clock up some unbelievable mileage. Relatively speaking, the average Peterbilt trucks are apparently doing something in the order of 10 times more mileage than the average European truck. Maybe there is a good reason why Volvo and Mercedes stays out of the North American truck market.

@Plen, again, that's nothing special. A quad is >50m which is ~175ft. They're scary if you're driving one lane across and in the opposite direction at 100km/h, but they are in no way secluded in Australia (the only place they're not permitted is in capital cities). Head out onto a highway and you'll see them everywhere.

Seriously though, you're talking about a double B which are figures A/C on the diagram: https://secure.wikimedia.org/wikipedia/en/wiki/Road_train#Rules_and_regu.... Semi-trailers get a lot, lot bigger. It's a pointless and futile comparison but I'm pretty sure we have the 'we have bigger road trains' thing in the bag. There's half a continent that can only be supplied by truck, after all. Is it really a competition?

@Plen...FYI. The Europeans own 3 US truck manufacturers.

Freightliner = Daimler AG (Mercedes Benz)
White = Volvo
Mack = Renault

Kenworth, Navistar and Peterbilt are in US hands.

Chalk another innovation up for my new hometown of Knoxville. Any little bit of technology driven energy efficiency is great.

Could some kind soul explain why American lorries are a completely different shape from European lorries?

European lorries are typically flat fronted, with the engine underneath the drivers seat (I think)

American lorries have the engine sticking out sideways in front of the driver (like a 1940's limo).

Why is this?

@ hypocrisyindeed .... holy cow. Imagine you are driving on a 'slight' downhill and you see one of those trucks in your rear-view mirror. Then you think to yourself, "I hope his brakes are in perfect working condition." or.... you are approach one of those monster rigs from the opposite direction and then you notice in a distance, another car wanting to overtake him.... but that car is now in your lane..... !!!

@ schwarze - you have just proven that even the Europeans know there is something special about American trucking technology (and worth while buying).

@ kingtran ... American "lorries" tend to have much bigger engines, not easy to fit under a cab. Also, American "lorries" tend to have a "sleeper cab" section for the driver. When doing a long trip, he can pull into a service station and sleeps in his own cab. Most of these cabs are well decked out with TV, fridge, little stove, etc. Now if you have to raise the Cab at an incline every time you want to check the oil, the driver risks having his beer fall out the fridge and we all know that is simply not cool.

@kingtran - The main reason trucks in North America have the engine out front is because it looks better, and regulations restrict the trailer length, rather than the overall vehicle length which is what Europe does. There is some weight cost to having the engine out front - about a ton or so.

@plen - I'm afraid a standard European truck with a single trailer is 40 tons, so the cross-boundary regulations do actually allow a bigger size than US federal standards. It's probably also worth mentioning that here in the UK there would be as many trucks that have driven their loads from Turkey as there would be trucks in California that have driven from the east coast, so the distances driven are similar, even if the places driven through are much more heavily populated. There's no deserts between Turkey and the UK, but the Alps and the Rockies are of similar magnitude. American trucks are certainly special to look at, and have much more glamour than European ones, but in terms of raw technology, the European standards are probably higher.

@S.D. - It would have been nice to have some perspective on how this compares to the much more engineered trailers which are in wider use on this side of the pond - for example the teardrop trailer at http://www.donbur.co.uk/gb/news/teardropmktwo.shtml whose predecessor is quoted as giving an average fuel saving of 11.3% in the fleets it's been installed in (ranging from 4% to 20%, depending on weight and speed).

@ ambrosenuk - just to let you know - I had a shipment of 50tons (metric) brought over and it came in a 52ft single trailer rig (with the drop axle lowered).

I don't dispute that trucks can run from the UK to Turkey and maybe even further to Moscow. But the rate at which trucks move up and down is related to the open highway structure, in which case the Americans are still the leaders.

Don't be mistaken, the single biggest driving force behind an economy is access to markets. You could quite literally connect the rate of GDP growth to the speed at which freight can travel across a country. Given that the USA is still the biggest economy in the world, you can be sure the Americans focus on opening up their bottlenecks, whether it is road infrastructure blockages or truck haulage capacity.

In fact the freight rail industry went under in the USA because of the success of their large truck rigs. In Europe, the rail freight industry can still compete against trucks because of the road infrastructure bottlenecks and the ability to send bigger bulk on rail. Thus American trucks clock up far more mileage and need to be built for greater endurance.

The US trucks don't look elegant, more brutish than anything but give them respect, they are impressive workhorses. If you look at the Aussie Train Trucks that pull the biggest loads, you may notice a similar design to the American trucks, this is not a coincidence.

@ ambrosenuk - just noticed your other post, thought I'd clarify a point. The engine in front was more popular among drivers, due to ease of access to the engine. Most trucks are run in an owner-operator system, truck drivers tend to also own their trucks and are constantly nursing their trucks - ease of access to the engine is very important. The US did have a era of cab over engine trucks (like Europe) but when they realised that there was no benefit to regulating overall truck length, the laws were relaxed. The demand went straight back to engine in front, again because drivers prefer ease of access....and not spilling their beer when tilting the cab.

oh geez, my colleague has just pointed out that Cab Over Engine configuration in trucks has far worse aerodynamics than the engine in front configuration. Also driving on top of the front wheels, makes for a noisier and more bouncing in the driver's cab. The US trucks are thus more fuel efficient from an aerodynamic point of view and more comfortable to drive. Perhaps not everything the Americans do is so retarded after all.