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Experimental device may keep trucks from jack-knifing


August 29, 2012

A new device could help keep transport trucks from jack-knifing (Photo: Shutterstock)

A new device could help keep transport trucks from jack-knifing (Photo: Shutterstock)

If there’s one thing that truck drivers don’t want their articulated tractor/trailer rigs to do, it’s jack-knifing. This typically occurs when the tractor skids on the road, and the momentum of the trailer causes it to swing out from behind, ultimately resulting in the tractor and trailer being folded up against one another – not unlike a jack knife’s body and blade. The folded rig usually ends up blocking the road, and the tractor can’t undo the situation under its own power. Fortunately, Greek researchers have recently created a system that they claim could greatly reduce jack-knifing.

First of all, there are already some technologies that help reduce the risk of a jack-knife occurring. These include anti-lock brakes in the tractor, electromagnetic brakes in the trailer, and devices that limit the angle between tractor and trailer at higher speeds. According to University of Patras engineers Nick Koussoulas and Stamatis Manesis, however, nothing tried so far has been sufficiently reliable.

What they have devised is a new type of kingpin. The kingpin is the junction where the tractor and trailer are joined, and it is normally situated in one static location on the rear of the tractor. The new kingpin, however, slides linearly, parallel to the tractor’s rear axle. In this way, sudden movements of the trailer result in the kingpin temporarily sliding over a bit, instead of having the trailer swinging out across the road.

Of course, a sliding kingpin could make regular driving of the rig rather challenging. That’s why the servo-driven sliding function would only activate in emergency situations, such as during hard braking – otherwise, the kingpin would remain fixed in one spot on the tractor.

So far, models of the system have reportedly indicated that it should “constrain jack-knifing to very low limits for a wide range of vehicle loading and road conditions.” The researchers are currently in the process of patenting the technology.

Source: Inderscience

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

The problem is that the trailer has started sliding. I think the solution is either aerodynamic control surfaces or deployable ice blades.


A Servo operated kingpin would work....

SB, remember that counter-steering in a car doesn't achieve anything until after the rear end has started to break loose....

Likewise the servo actuator on the kingpin acts to "counter-steer" the trailer and avoid the slide progressing towards accelerated instabillity...

The best safety device for trucks is ABS / ESP... meaning you didn't lock up the brakes (on ice or gravel..) and run into whatever you were avoiding at "full speed", and then wrap the truck around everything else on the road.....

If this works to keep it all in a straight line then it is an advantage....

Many different alternatives could be done to achieve the same result....

Have they actually put a full ESP system on any trailers?? because as it works to stop a car from rotating, it would also stop the trailer....


How about a simple turn limiter in the turret for for any speed over 20mph? All you need is a couple of strong springs on either side and a electromagnetic tooth a few inches away that hits the spring at the 15 or 20 degree mark limiting it to a 30 degree max turn, on either side. It should be permanently deployed at speeds over 20mph under its own weight, but it is then electromagnetically raised up out of the way so the turret can turn all the way at low speeds for tight maneuverability. I'm surprised it has not been built already it is so simple and cheap.

AnOld BlackMarble

Springs to stop the rotation of the trailer would have to be quite huge to stop from rotating such a great mass with a great lever... The problem of jack-knifing comes from the fact that the trailer is pushing on the tractor behind its center of mass. An "easy" fix would be to relocate both the kingpin and center of mass of the tractor so that the trailer actually lines up with the tractor under braking. This would not solve the wheels locking though, so ABS or ESP on the trailer is also a great idea.

Forest Fab

Whatever happened to the system whereby the ability of the tractor and trailor to turn relative to eachother was constrained by the action of a kingpin brake that came into play when the road wheels were braking hard?

With modern sensors that kingpin brake could be released if the unit was trying to form an angle between the tractor and trailor that would result from the driver's steering action, thus taking full advantage of the anti-lock braking system to enable the driver to steer round any obstacles.

Mel Tisdale

For the record, the kingpin on a tractor-trailer is a large metal bolt affixed to the underside of the trailer. It couples to a latching mechanism on the tractor known as the 5th wheel. I'm curious whether the system described in the article is actually a moving kingpin or moving 5th wheel.

Vic K.

Experimental 4 wheel Bose suspension reacts extremely fast to give extraordinarily improved ride comfort on roughest road. If that fast reacting program and hardware can be adopted to work for this purpose it should work out great.


I seem to recall anti-jack-knifing devices being around in the 60s.


sounds like a great idea which will sell in huge numbers unlike the deployable ice blades someone suggested


FF.. forgetting one important thing.... Axle loads.... Trucks are designed to carry stuff... the distribution is set-up so that the correct weight distribution is on all of the axles under normal operation..

Sure the triler pushes on the Prime mover behine the Prime mover's centre of mass, but with a load on the turntable, that load becomes part of the 16 tonne mass on the rear tandem drives.. (or single drives in countries without tandems) THe truck doesn't actually know where the mass comes from, the fact that the axles see the weight is all that matters...

This solution takes a control approach,..

ANOBM.. springs could be dangerous too... setting up potential oscillations that make the situation on the prime mover worse. Also a sliding trailer, hitting any sort of "hard stop" will, either shear the "stop" off, or start the tractor (prime mover) spinning due to loss of traction earlier than it would otherwise. Kinetic energy and momentum are powerful factors. (Was going to say force, gotta be more precise)


This isn't just an ice issue- rigs can jackknife on dry ground.

Ice blades&aerodynamic surfaces from the first commenter? How big would they have to be to manage 80,000+ lbs. that are out of control?

Sudden side-winds are often a factor with rigs- not as much in little cars.

You have so many variables with such a large mass that this is not likely to find one sudden easy,solution.

What they are proposing will help AVOID a jackknife- not stop one once it starts anyway.

I have had a CDL to drive all rigs including doubles&triples (which are actually triples and 5-ways,if you count the converter dolly trailers that connect the big trailers...what about them?) since CDL's first came out.

I doubt many of these commenters have any experience driving 80,000 lbs. across black ice.

Better automatic chains would be a better step for ice safety for rigs- jackknifed rigs need more than a side-to-side sliding kingpin.

Anything that moves is more likely to fail than something that is stationary.

Most rigs on the road already have improperly adjusted brakes which contribute to jacknifing!

That's despite the fact that the vast majority of rigs have so-called "automatic slack adjusters"...

This is not a simple problem and is not likely to find a simple solution- it's good that they try but I think that a side-to-side trailer hitch is likely to create more problems than it's worth over a period of time.


windykites1 said "I seem to recall anti-jack-knifing devices being around in the 60s."

They were indeed, and consisted of a hydraulically operated multiplate brake mechanically similar to a motorcycle clutch attached to the kingpin and operated by the braking system so that the tractor and trailer were locked together when the brakes were applied.

Didn't catch on.


trucks in the usa have had antilock braking systems on trailers and dollys for years. www.bendix.com www.meritorwabco.com Most people have no idea the enormous amount of gross vehicle weight these guys are driving on the road with. Very soon in the U.S. they will weigh 125000 lbs or there abouts...and that isn't for a dual trailer. In the end physics always wins.


I never saw a dry pavement jackknife that didn't start as an emergency braking maneuver. I have seen trucks blown over by the wind.

I like Slowburn's Idea for aerodynamic control surfaces. For normal purposes they could perform as a boat tail but when the trailer tires start to slide the side panels act as rudders and the top panel as a spoiler to give the tires more traction. A spoiler that deploys at the front of the trailer could help as well by keeping the tractor tires from breaking loose.

I can see how Ice skate like blades that spring down when the trailer tires loose traction could work on snow and ice or a dirt road but on a paved road it might make things worse.


Sliding wheels have less friction with the road than rolling wheels.

I recall a news report from the 80's or early 90's when it was a popular thing among some truck drivers to disconnect their front wheel brakes on the tractors.

Their thinking was with the front wheels unable to lock up they'd avoid jackknifing because they'd always have steering control.

It took the DOT taking a bunch of truckers to a test facility and having them do panic stops with and without front brakes to show them that without front brakes the rear wheels lock up and skid easier because they have to bear their normal load plus what the front brakes would.

With the rear wheels locked up the tractor would slew sideways every time. With all the tractor wheels locked it'd slide straight, with the still rolling trailer wheels acting as a drag.

An antilock brake system that varies the amount of on time from front to rear would aid a truck to stop straight in slick conditions. If the front wheels were allowed to lock up a little and the trailer wheels never fully locking up until the truck stops moving, that would provide the most stability.

Where current antilock brake systems fail miserably is in conditions so slick that a vehicle can still slide even after all the wheels are locked up.

The ABS is programmed to assume the vehicle is stopped when all the wheels are not rotating. What an ABS should also sense is if the vehicle is actually not moving when none of the wheel sensors indicate rotation. If that input says "Hey! Still moving!" then the ABS control should continue to pulse the brakes.

The ABS failure can be seen by looking up winter crash videos in Seattle on youtube.

If you're sliding out of control down a slick hill and you're not feeling and hearing your car's ABS banging away - GET YOUR FOOT OFF THE BRAKE PEDAL SO YOU CAN STEER!!! Keep holding the brakes and you are riding an uncontrollable sled that is going to bounce around like a golfball in a clothes dryer.

Gregg Eshelman

Truck jack-knifes have complex causes. There are steerer skids, drive axel skids and trailer tandem axel skids. There are variable and unknown road conditions. There are idiot drivers, both inside and outside the tractor. The load on the trailer and drive axels varies with the total weight range from around 32,000 pounds empty to 80,000 loaded. This is a real challenge for brake designs. The steerer axel load is almost constant which helps but you do get “weight transfer” to the steerers when braking.

Air brakes and ABS have made tremendous advances in stopping ability but improvements are still needed. Most trucks and trailers have both but maintenance, especially on trailers is not optimal. Vehicle proximity sensing is becoming available. Road condition (water, snow, ice, dry and speed) sensing would be good if it could be made workable.

Most (over 70%) truck accidents are initiated by cars. I do not know of statistics related to jack-knifes, but I suspect the ratio is similar, if not higher since a typical jack-knife is caused by trying to stop too quickly for available traction conditions. The other general conditions are following too close and driving too fast.

I have been passed by a truck flying down a snow covered median. I have had a car sliding sideways just 25 feet directly in front of me. It was coming from an on-ramp and spun out trying to get on in front of me. I have no idea why the truck was going so fast in the median. Any truck driver could give you a long list of examples of idiots behind the wheel.

Changing the pay system of dollars per mile is a nearly impossible task but dollars per hour would decrease the speed incentive.

Owner/Operators are learning that driving slower earns more money by reducing fuel and other costs.

Improving braking would cost money but when an exhaust system now costs $20,000 the cost for better brakes would not be prohibitive.

Putting a recording video system in all trucks would be cheaper and would reduce accidents more than anything else I can think of. It would improve the driving skills of all drivers, both inside and outside of truck cabs.

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