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Aerodynamic Heavy-Duty Truck Trailer Cuts Fuel Consumption and Emissions By Up to 15%

Trailer with aerodynamic sideskirts.

Creating an improved aerodynamic shape for heavy-duty truck trailers by mounting sideskirts can cut fuel consumption and emissions by up to 15%, according to road testing by the Dutch research partnership PART (Platform for Aerodynamic Road Transport). PART is a partnership between TU Delft, TNT, Scania Beers BV, FOCWA Carrosseriebouw, Ephicas, Kees Mulder Carrosserieën, Van Eck Carrosseriebouw, Syntens, Squarell Technology, Emons Group and NEA.

Sideskirts are plates which are mounted on the sides of trailers, primarily with a view to underrun protection. The new aerodynamic design of the sideskirts substantially reduces the air currents alongside and under the trailer and thereby also the air resistance.

Initial driving tests with a trailer equipped with the aerodynamic sideskirts over a straight stretch of public road revealed a cut in fuel consumption of between 5% and 15%. Subsequent research comprising long-term operational tests by TNT displayed a fuel reduction of 10%.

These results confirm calculations and findings from the wind tunnel tests that had established that the observed 14 - 18% reduction in air resistance led to 7 - 9% less fuel consumption. In practice, the figures are in fact even better.

PART expects that the cost of fitting aerodynamically-shaped sideskirts will be recouped within two years. Furthermore, the sideskirts can be fitted to approximately half the trucks currently in use in the Netherlands as the skirts can also be retrofitted.

In 2005, 10,000 new trailers were taken into use in the Netherlands. With an average fuel consumption of 30 liters per 100 kilometers [7.8 mpg US], that translates into 750 million liters of diesel consumption in the Netherlands each year. We can cut fuel consumption by 5% or more for 50% of those trailers. That means a reduction of 50 million tons of CO2 emissions a year. This research can therefore result in a substantial, structural contribution to cutting fuel consumption and an annual saving of tens of millions of Euros, next to that cut in CO2 emissions by the road transport sector.

Together with this sector we have created a practical platform for further research and development, but we still need active government participation. Just obtaining permits for all the road tests has involved a huge amount of time, energy and frustration. The next step is realizing a practical partnership between the government and industry in order to put the solutions into practice.

—Prof. Michel van Tooren of TU Delft’s Aerospace Engineering faculty

Road tests have also already been initiated on boat tails. These constructions on the rear of a trailer ensure a reduction in the wake—the vacuum and air currents which arise when the trailer is moving. In theory, a boat tail could also mean a cut in air resistance of 30%, with a fuel reduction of 10 - 15%. These road tests should also confirm the earlier, highly positive results from the windtunnel.

Boat tails, however, are limited in practical use, in particular when loading and unloading—safety aspects and problems with exceeding maximum vehicle sizes prevent these being used for many types of vehicles.



It took them this long to figure it out. When you can draft behind a large truck, you are punching one seriously big hole in the air. It is pretty obvious.


Other studies like this have been done here
and companies like WalMart have been using these for years
and you know that if WalMart is doing it, it's for the bottom line (and not for environmental reasons).

So why isn't everyone getting getting a truck skirt? Especially those independent truckers that went on a silly strike a few weeks ago to protest diesel prices.

Mark Gutting-Kilzer

Rather than just covering a void, cannot the space beneath the trailer floor also provide useful storage or hauling space? Sure, place skirts over the wheels, but place cabinets below the floor.

My guess is the skirts will also serve to mitigate the spray mist ejected from the tire wells while driving on wet pavement - a safety hazard to moving traffic in the immediate vicinity.


Here's a company that sells them

I wonder how much these things cost?


Inflatable boat tail.

Also, whatever happened to the (I thought brilliant) idea of using compressed air jets out of nozzles on the rear to make the vehicle effectively longer and streamlined?


it seems to me that the biggest component of drag is the square tail. has anyone looked at the various components of drag (nose, wetted area, tail etc)?


This is a good idea also for safety reasons. Everyday a lot of peatons, cyclists and motorcyclists die under trucks wheels.


It seems that maybee a decade ago in Europe there was interest in installing inflatable spoilers on the end of trailers. It wouldn't help the first truck on fuel use but it would reduce the fuel consumption on the trucks following close. There must have been a GPS-device regulating the rear trucks engine speed for safety reasons. The main reason at the time was to be able to cram more trucks in the lane.


A 5-15% reduction in fuel consumption. That seems like pretty low hanging fruit to me. We are talking about billions of gallons of oil saved per year.

Honestly, I can't see a downside.

Gerald Shields

sjc, you said:

"So why isn't everyone getting getting a truck skirt? Especially those independent truckers that went on a silly strike a few weeks ago to protest diesel prices."

Waitaminute. I don't think anyone has thought about fuel efficiency with a truck much less a heavy duty or an 18 wheeler. I get the feeling that truck companies should be considering testing their trucks in a wind tunnel to improve fuel efficiency.


"Also, whatever happened to the (I thought brilliant) idea of using compressed air jets out of nozzles on the rear to make the vehicle effectively longer and streamlined?"

probably the cost of installing the system too high; also doubtful if you save more energy than you spend compressing the air.


One can also place partition pieces out in front of the nose of a truck and create a more streamlined shape.


Renault tried the air jet thing in a concept car

They put the jets on the top of the rear which would be a problem for container trucks.

But you could do it for buses, SUVs, MPVs etc.

However they quote the savings at 80mph which is probably faster than they want people to go.

[ Green types anyway ]

I wonder could you electronically link trucks together so they could slipstream (and keep it safe) - imagine being hit by a convoy of 10 trucks!



You attributed Karkus' quote to me. I saw a video of a pickup truck that hit the side of a jack knifed trailer and sheared the top of the pickup cab right off. It is a safety issue as well as a fuel savings and by extension, national security issue to get more mileage out of truck travel.

I would guess the reason that independent truckers have not done something like this is cost. They are paying for their rigs and fuel, they do not want to pay for this. Maybe the government and tax payers could help. It is good to save fuel for lots of reasons and when you combine safety, it is in the public interest to do so.

Harvey D

Didn't everybody know that moving a very large brick at 75-80 mph takes a lot of energy. Truck/bus builders and operators should have known that and figured ways to reduce drag decades ago.

John Taylor

The fuel saving idea is not really new.
Side skirts help, but so will underskirts, as will either boat-tails or some other rear square-reducing method to improve airflow.

However, often trailers are owned by the transport company, while the truck is owned by the independent trucker.

It would be nice to see side-skirt and under-skirt kits made available for all standard sized trailers, with perhaps a tax incentive or grant program to have them installed, and perhaps extra charges at tolls for trucks without them.


Well, John beat me to the answer. Independent truckers just own the rig, not the trailer. They get a contract to go somewhere, latch it on, and bring it somewhere else.


I am seeing and expect to see more good ideas being used by the large in house over road truck operators such as Wal-Mart. They probably control both the truck and the trailer.

I would be interested in seeing a trade off between this type of add on and the reduction in speed in 5 mph increments. My guess is you could get some very quick results close to these just by changing driving habits.


Another option would be to have a spoiler that extends from the front bumper at highway speeds to improve the aerodynamic profile of the vehicle.


Frontal configurations have the most effect on aerodynamic drag as compared to rear aerodynamics. Frontal streamlining & rear boattails make the truck-trailer combination longer which are already at the maximum legal length. One method from 1960's station wagons would be an aluminum fixed curved spoiler at the top rear of the trailer(& spoilers along the verticle rear edge if possible) which would skim boundary layer air & force it to fill the vacuum behind the trailer. These devices would often be subject to damage.

Making the sideskirt bottom strong enough to carry extra cargo would make placing cargo down between the wheels difficult & would require extra power equipment other than folklifts. Special strapping so forklifts could lower cargo between the wheels would really reduce a cargo area already pretty small.


Question. In the US many truckers are independent. They own and operate their rig. Is that true in the EU?

It seems to me that independent truckers would have a greater desire to maximize profit and employed drivers would be more content to follow parameters set by the employer. And employers will at least try to look socially responsible by minimizing fuel consumption.

As for all this drag reduction. The Arabs announced an embargo in 1973 during a war with Israel. For a month or so there were shortages in the US. In the aftermath the merits of various skirts and shapers were studied and many were added to trucks. The current rising fuel costs will lead to further adaptions.

But this time I expect we will see mandated improvements rather than leaving it up to the truckers.


I beliefe most truck drivers are just contractors or employed staff here in europe. The percentage of truckers
owning the rig is probably less than double-digit.

Even at european diesel prices (currently at around 7,70 USD/gal) most trucks are speeding (typically, the speed limiter is set by default to the legal speed limit + 10 kph; however, a lot of trucks are going even faster, and this not only downhill...).

Obviously, the gain from being on time at all cost is larger than the cost of fuel - still. It seems to happen
a lot that if a driver is caught speeding with and has to hand over his driving licence, he is immediatily fired and replaced by another driver... Staff cost is
probably low too, as these companies employ mostly eastern europe citizens (low wages there).

Not really a job I'd like to have.

Anyway, obviously fuel at nearly 8 USD/gal is still way
too cheap to really think about transportation and
logistics in a grander scheme (ie. using rail instead of
road for distances > 200km; currently, long distance truck traffic is growing rapidely with typical routes around 1500 km.

Unfortunately, the oil price is not fundamentally high,
but the USD is weak; I'd think with USD and EUR were
still around parity, and Oil being that high then,
this would really make people reconsider (that'd be around 12 USD/gal for diesel).

Any bets when this mark will be exceeed?


Mahonj, i like your idea. In some places it wouldn't work so well when it's icy(do you really want the computer driving when conditions are marginal) however i was thinking maybe linking 2 or 3 trailers together, i know they already do 2 at a time but it seems few and far between and far more often than not you see just the 1 trailer at a time


One idea I thought of and have heard about are cruise control range sensors. They estimate that many rear end collisions and pile ups on the highways could be eliminated if the range distance between the car in front and the car in back could be computer monitored.

Not only would it prevent accidents, but a highway train of sorts would reduce drag and fuel consumption. People in Southern California routinely travel at 70+ mph with 3-4 car length gaps between them and the car in front. You might think you were on a race track.

This is not a good driving habit, because reaction time is 1/2 second at best and you are in the guy's trunk in a blink. You hear about these accidents everyday and I am amazed that there are not more of them.

With the range sensor computer, you could run at that speed and distance with a safety margin at the same time. Now on the freeways, if you allow 7-8 car lengths, somebody will just change lanes into that space. If we can save fuel and save lives at the same time, that might be a winning combination.

Brad Godfrey

realarms: isn't gas in the US not at like $3.50 a USG or something like that? i think they'd start thinking more about their choices even at $4 or $5 a gallon

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