What is a Jacknifed Lorry?
Discussion
Sorry if I've misspelt the title.
My understanding presently is that this is an articulated lorry which, for some reason, has had the trailer over run the cab so the cab ends up at 90 degrees to the trailer, or maybe slightly more.
If that's the case, then:
i) What causes it to happen?
ii) Why does it take so long to sort out when it happens on a motorway?
I originally thought you could just reverse the cab, straighten up and drive off. But the more I think about it, the more I think there must be loads of damaged caused to either cab or trailer of both. If the hitch on the trailer's damaged do they replace it or bring in a MASSIVE Low Loader truck to take the broken one away?
I'm sure there's people on here who know chapter and verse on this.
Cheers
My understanding presently is that this is an articulated lorry which, for some reason, has had the trailer over run the cab so the cab ends up at 90 degrees to the trailer, or maybe slightly more.
If that's the case, then:
i) What causes it to happen?
ii) Why does it take so long to sort out when it happens on a motorway?
I originally thought you could just reverse the cab, straighten up and drive off. But the more I think about it, the more I think there must be loads of damaged caused to either cab or trailer of both. If the hitch on the trailer's damaged do they replace it or bring in a MASSIVE Low Loader truck to take the broken one away?
I'm sure there's people on here who know chapter and verse on this.
Cheers
I was under the impression that it was when the driver has had to stand on the brakes and the tractor slows down, but the rear axels on the trailer lock up causing the trailer to overtake the tractor.
Obviously there's a lot of momentum (due to weight) involved so can cause considerable damage.
Usually happens when those pesky prozzies aren't behaving and you just gotta kill 'em
Cheers
The Moose
Obviously there's a lot of momentum (due to weight) involved so can cause considerable damage.
Usually happens when those pesky prozzies aren't behaving and you just gotta kill 'em
Cheers
The Moose
I'd always assumed the reason it takes so long to clear up, is that it's possible for the angle between the cab and trailer to be greater than the maximum steering input that the cab is capable of, so it's not possible to reverse without making the jack-knife angle worse. This is certainly a very easy situation to get into when reversing a trailer.
Edited by kambites on Thursday 21st April 09:01
As said its when the rear axle of the unit loses traction for whatever reason. Slamming brakes on can cause it, specially in bad weather. On snow/ice the auto exhaust brake can easily lock it when it kicks in if you forget to turn it off. Or what happened on the A1 near me a wagon went straight on on a slight bend hitting the Armco on the outside, this caused a jack knife as the trailer kept going an pushed the uni round.
Re not been able to reverse out of it. If there was no damage then you would easily reverse out of it, there's some serious lock on an artic that'll pull the unit round. Plenty of places you drop at in artics you have to deliberately jack knife the trailer round to be able to get on the bay etc. Wagons going to industrial estates/shops appear to be an afterthought!!!
The reason why they take so long to clear up though is when a jack knife happens at speed there's normally a lot of damage to unit, trailer, where it's landed/got beached or whatever else it's hit whilst out of control!
Re not been able to reverse out of it. If there was no damage then you would easily reverse out of it, there's some serious lock on an artic that'll pull the unit round. Plenty of places you drop at in artics you have to deliberately jack knife the trailer round to be able to get on the bay etc. Wagons going to industrial estates/shops appear to be an afterthought!!!
The reason why they take so long to clear up though is when a jack knife happens at speed there's normally a lot of damage to unit, trailer, where it's landed/got beached or whatever else it's hit whilst out of control!
Couple of things can cause a HGV to jacknife, most common is under emergency braking, 30 ton of trailer versus 7-8 ton of tractor unit means the trailer will just push the tractor unit until either it stops/hits something.
Another cause of jacknife is when the traction wheels of the tractor unit loose grip, i.e. when exiting a roundabout, driver gives it gas hits a patch of oil and this causes the tracor unit to spin.
Problems that are caused by a jacknifed lorry are airlines will break, rendering the vehicle immobile. Fuel tanks can be ruptured, and this can obviously cause major delays/problems dealing with the spillage. Damage can also be caused to tractor unit, mainly to the cab, trailers are normally pretty un-scathed, most of the damage occurs to the tractor unit.
Recovery of the vehicle can be made more difficult depending on the position, could be parked up and embankment, down an embankment, on top of a barrier etc. It will need an air feed into the vehicle, then require winching backwards, basically the way it went into the position. It will normally be recovered by an underlift, basically lifted at the front, and the complete unit recovered as one.
Another cause of jacknife is when the traction wheels of the tractor unit loose grip, i.e. when exiting a roundabout, driver gives it gas hits a patch of oil and this causes the tracor unit to spin.
Problems that are caused by a jacknifed lorry are airlines will break, rendering the vehicle immobile. Fuel tanks can be ruptured, and this can obviously cause major delays/problems dealing with the spillage. Damage can also be caused to tractor unit, mainly to the cab, trailers are normally pretty un-scathed, most of the damage occurs to the tractor unit.
Recovery of the vehicle can be made more difficult depending on the position, could be parked up and embankment, down an embankment, on top of a barrier etc. It will need an air feed into the vehicle, then require winching backwards, basically the way it went into the position. It will normally be recovered by an underlift, basically lifted at the front, and the complete unit recovered as one.
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