proper seat belt function (rear end collision)

My fiance was involved in an accident about a month ago (in our 06.5 Jetta TDI) and we are both concerned about whether the seat belt functioned properly in the accident.

She was rear ended by an SUV while waiting to make a left hand turn. The SUV sustained pretty substantial front end damage and was probably travelling at about 35mph (just a guess) when it made impact.

My fiance was injured when her face hit the steering wheel. She's doing much better since the accident, but will require some (more) dental work in the future.

Should a seat belt prevent someone from hitting the steering wheel if the vehicle is hit from behind? It obviously stopped her from going through the windshield, and she is very lucky that she wasn't injured more seriously. But there was no bruising from the seat belt, which makes me wonder if it restrained her properly upon impact. Anyone have any insight here? Thanks,

Ryan

BTW... we're still waiting for our Jetta to return from the shop, and are suffering with a Chevy Cobalt in the interim.

LongWayHome said:

(snip) Should a seat belt prevent someone from hitting the steering wheel if the vehicle is hit from behind? It obviously stopped her from going through the windshield, and she is very lucky that she wasn't injured more seriously. But there was no bruising from the seat belt, which makes me wonder if it restrained her properly upon impact. Anyone have any insight here? Thanks,
Ryan

Click to expand...

__. Ryan, I know that it's not what you want to hear but there's no way to answer your question. Seat belts have to be built with a certain amount of "give" in them -- it just may be that the belt (working together with the car body, seat design, etc.) stopped your fiance from sustaining a broken neck but -- with the right amount of "give" to prevent the more serious injury but that right amount of "give" meant that she sustained the relatively minor facial injury. Also, it would be good to know if she had the upper belt location adjusted properly (I would guess it adjusts on the A5 - it does on the A4). Did the belt buckle come loose in the accident? Where was the steering wheel located, in terms of telescope and tilt?

__. Seat belt systems are complicated in the way that they work. So, without a very thorough accident-reconstruction analysis, it would be impossible to say exactly whether her injuries could or should have been avoided.

__. But I'll have to add that I'm personally very impressed with VW belts. The system in my A4 sedan protected me when I was hit by a drunk running from the cops at about 115 MPH last November. I was doing the speed limit in the right hand lane; he hit me, spun my car around twice, and put my car in the ditch. My car rolled over (more like spun over because when it hit the roof, it was sliding backwards down the ditch) and the cops measured the skid marks from the roof of my car for 60 feet along the ditch. Then there was a gap of 17 feet where there were no marks and my car came to rest on all four wheels, facing the traffic, about 4 feet back towards the road surface from the ditch. I suffered a scrape on my elbow (center console, I expect) and some separated ribs (ditto), a broken toe (kicked the back of the clutch pedal) and a slight scrape on my left jaw (side curtain air bag???). But as I was sliding down the ditch hanging off the belts, I remember thinking "I really don't want to hit my head on anything" and I didn't. I did have big belt bruises on both hips and a small one on my shoulder.

__. I'm sorry to hear that your fiance suffered any injury at all and I hope that there were no extinuating circumstances from the belt. And I hope that they'll get her fixed up just fine and that your car comes back in good shape soon, too.

Can you go to the car now and tug on the seatbelts? they should lock when you yank on them.

-J

That does stink, sorry about the accident.

The seatbelts (front at least) have "pyrotechnic tensioners", that detonate to snap the slack out of the seat belts before the belt locks in the event of a frontal collision. I believe the detonation is activated by the driver's air bag circuit, and happens when the driver's air bag deploys.

My guess is that since this was a rear collision, the secondary frontal collision that caused you fiance to be thrown forward and into the steering wheel was not sufficient to activate the air bags, so the selt belt tensioners did not function. The tensioners are completely different than the seat belt locking mechanism. The tensioners detonate (explode) to achieve their action and are a one-time use item. The locking mechanism is a mechanical lock (pawl) activated by centrifugal force of the sudden vehicle decelaration. This is what locks the seatbelt when you yank on it. The pyrotechnic tensioner just takes the slack out of the belt by pulling on it before the locking mechanism activates, thus keeping you pined in your seat when the belt lock catches.

I'm not sure when these pyrotechnic tensioners appeared, but I bet it was when air bags appeared. I think the idea is to prevent front occupants being thrown into a deploying air bag, which could cause injurys in itself.

Here is a description:

"Reacting in a thousandth of a second

Besides this primary protection, modern cabins are constantly improved through the addition of fittings which have considerably increased occupant safety during the100 thousandth of a second a collision usually lasts. During this time, the object is to keep the passengers isolated from the cabin and to absorb the impact of contact with its components. "The complementarity of the seat belt and the airbag are at the core of this protection" says Jacques Bariller. An increasingly "intelligent" airbag coupled to a pyrotechnic re-tensioner which gathers up belt slack and secures the passenger firmly into his seat are key elements of this technology. These two elements have reduced thoracic injuries thanks to an effort limiter which gradually releases seat belt strap tension from 400 kg of thoracic pressure (the limit for people with weak chests). During a collision, belt slack can reach 20 cm, making the combination of the pyrotechnic re-tensioner, the effort limiter and the airbag essential. PSA Peugeot Citroen is progressively equipping it’s vehicles with six airbags (frontal, Lateral and side-curtains) for the most complete passenger protection under the widest variety of impacts. ......"

--Nate

VWs have had pretensioners since 1995 in the US.

I spoke to the body shop guy on the phone yesterday. He mentioned a mechanism (I don't think he referred to it as a pyrotechnic tensioner, but that's probably it) that 'exploded' when the accident occured, and he assured me that it had functioned properly at the time of the accident. One of the final steps in the repair process was an airbag specialist coming out to reset the seat belt (probably the tensioner, since the airbag didn't deploy and should be fine)

We will definitely give it a close inspection (and a tug or two) when we pick it up. My impression from talking to him, reading the info here, and research elsewhere, is that seatbelts won't always prevent a face to face encounter with the steering wheel, but will definitely help lessen the impact.

Thanks for all the info and the good wishes.