# Decel Gs in an accident

27 replies to this topic

### #1 meb58

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Posted 11 November 2009 - 19:38

Car A is an 8,000lb truck sitting still with the brake firmly applied and car B, 2,300lb sedan hits the truck at an estimated 45mph. The car is driven under the truck far enough to cause the oil pan to scrape the road but has moved the truck 16' forward while its brakes were applied - the driver prepared for the hit (I would have accelerated away). This all occured on a dowward grade I estimate to be 8% = to a 8' drop in 100' or a 4' drop in 50'.

I saw exactly this toady...the driver of the car unfortunately died; he was not wearing a seat belt and the EMTs said his chest was like jello. An elderly gentleman...easy to picture his wife, children and grandchildren getting some bad news.

I think I've read a human can absorb a ~ 9g decel...but a steering wheel in the chest adds complexity...this feels like significantly more than 9gs to me...12-13?

Edited by meb58, 11 November 2009 - 20:17.

### #2 DaveW

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Posted 11 November 2009 - 20:35

This might be relevant:

http://www.stapp.org/stapp.shtml

### #3 gbaker

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Posted 11 November 2009 - 20:45

It is generally believed that a human can withstand decelerations up to the 150-180G range, 25-30Gs if no head and neck restraint is used.

A = (Vt ^2 - V0^2) / 2s, where

Vt = velocity at time t,
V0 = velocity at time zero,
s = distance

G = A/g

G = A/32.17

### #4 meb58

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Posted 11 November 2009 - 21:56

Thank you DaveW!

gbaker...I had no idea that humans can withstand between 150 - 180g range. I beleive the steering wheel killed him.

### #5 Greg Locock

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Posted 11 November 2009 - 22:14

applying the brakes was a bad idea.

So far as what human beings can take, 10g is a sustained survivable whole body acceleration, Gregg's numbers are the short term spikes you see measured on the dummy itself, whereas I'm just working out the average sled deceleration.

Very hard to get precise numbers from tha sort of information,

Anyway, KE before the accident is 1/2*Ma*v^2=1/2*1000*(45*1.6/3.6)^2=200 kJ

Work done moving the truck forward assuming locked wheels=BE= mu*4000*10*5=100 kJ if mu=.5

those two are surprisingly close. The difference between them is the energy absorbed by crushing the sturcture, which is the average decel force times the crush distance, say 1m.

Also v^2=2*a*s, s=6 m allowing for crush

a=(45*1.6/3.6)^2/2/6=33 m/s/s, just over 3g ON AVERAGE, maybe two or three times that peak (looking at some random data off the web)

So if he'd been wearing a seatbelt he'd probably be nursing some bruised/cracked ribs and black eyes. Suicide by libertarianism.

There's a couple of cross checks you can do, to refine that estimate, 33kN*1 m of crush should be the difference in KE-BE, which it isn't, ie KE=BE+CE where CE is the crush energy

I've ignored the hill.

### #6 gordmac

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Posted 13 November 2009 - 12:01

From what I remember regulations govern the maximum deceleration and duration for various bits of the body, long time since I dealt with this stuff but I may be able to find the values if anyone is particularly interested.

### #7 scooperman

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Posted 13 November 2009 - 13:06

"the driver prepared for the hit (I would have accelerated away)."

There was one humorous thing that happened. Nissan driver turned out to be an illegal immigrant, no driver license or insurance. He spoke Spanish and a few words of English, the Highway Patrol officers spoke GoodOlBoy and a few words of Spanglish. After the officers were done filling out all the paperwork, they called a tow truck to come and haul the Nissan away. The Nissan driver was handed a pile of paper, they explained that they weren't arresting him but he was going to have to appear in court. He just kept smiling and nodding. Then they told him he could go. So he tried to get in the Nissan, to drive it away. "No no no, you can't drive." "I go?" "Yes you can go"...tries to drive. "NO, you can't drive the truck." "I go?" "Yes you can go"...tries to drive. "NO you can't drive the truck." "I go?" This went on for a while, they were still trying to explain it to him when I left.

### #8 gbaker

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Posted 13 November 2009 - 13:24

Thank you DaveW!

gbaker...I had no idea that humans can withstand between 150 - 180g range. I beleive the steering wheel killed him.

Those values assume no steering wheel or other intrusion, and is the range at which the heart separates from the aorta or other soft tissue damage occurs in the thoracic cavity.

Keep in mind that "withstand" means the driver is alive after the impact. That's the only measure of success. Drivers have survived ~130Gs on the track in a tight cockpit, but a crash dummy on an open sled will lose its arms on the rebound at impacts much lower than that.

### #9 meb58

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Posted 13 November 2009 - 13:30

I wrote, "...I would have accelerated away." with experience as my teacher, not foresight. I've driven over 3 million miles thus far in my life and much has happened in all those miles...mostly good thankfully.

We learned the gentleman was 85 years of age and apparently had a heart attack just before hitting the F350.

"So if he'd been wearing a seatbelt he'd probably be nursing some bruised/cracked ribs and black eyes. Suicide by libertarianism."
As a conservative, I would have stepped on the gas and driven right thru the F350...my will alone would have made it so...but my friends and company are small in numbers. I submit, omitting the above driver's condition, more velocity might have proven beneficial...though not for the driver in the F350. Just an interesting thought exercise...

Edited by meb58, 13 November 2009 - 13:31.

### #10 MattPete

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Posted 15 November 2009 - 04:48

"So if he'd been wearing a seatbelt he'd probably be nursing some bruised/cracked ribs and black eyes. Suicide by libertarianism."

Live free and die?

### #11 Greg Locock

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Posted 15 November 2009 - 07:14

Here's the allowable sled pulse for a belted occupant in the EEC I think

http://www.dft.gov.u...ty_022736-1.gif

http://www.nhtsa.dot...Rest/Index.html

Edited by Greg Locock, 15 November 2009 - 07:26.

### #12 mariner

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Posted 15 November 2009 - 17:58

Following on from the different EU and US Federal rules I am wondering which safety standards are , overall, the toughest for mfrs to met, the EU ones ( including the NCAP tests) or the US federal ones. A long while ago the US had tougher passive safety standards but I would presume the EU rules have caught up.

I guess Greg works for the Holden opposition in OZ so I am sure he would never even speak to a Holden person (!) but as Holden shipped the Commodore to the US as the Pontiac GTO and to the EU as the Vauxhall Monaro could he guess which set of rules gave Holden the most rouble?

### #13 Greg Locock

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Posted 15 November 2009 - 22:53

Following on from the different EU and US Federal rules I am wondering which safety standards are , overall, the toughest for mfrs to met, the EU ones ( including the NCAP tests) or the US federal ones. A long while ago the US had tougher passive safety standards but I would presume the EU rules have caught up.

I guess Greg works for the Holden opposition in OZ so I am sure he would never even speak to a Holden person (!) but as Holden shipped the Commodore to the US as the Pontiac GTO and to the EU as the Vauxhall Monaro could he guess which set of rules gave Holden the most rouble?

As I look around the office I see one ex bentley, two ex lotus, two ex holden, two ex ford of europe one ex ford usa and one ex mitsubishi and one ex subaru. FWIW I worked on a holden project before I came here. So there aren't many secrets.

There isn't much difference in complexity of the Euro/Australian vs USA crash. The big difference of course is that USA crash is no seatbelts, so you need a completely different airbag and calibration. I'd guess there wasn't much in it structure wise. Back in the day we did have different structures because of the different bumpers due to the Federal low speed crash requirement, but I don't think the differences were big, just the bumper bar. Actually the legal requirements are pretty easy, NCAP is the bugger, and entirely controls the crash development program.

### #14 alexbiker

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Posted 15 November 2009 - 23:53

As a prehospital and intensive care doctor, I have to say decceleration was probably irrelevant here, and you're right in saying the steering wheel killed him. The scale of forces required to turn a chest to "jello" would be an order of magnitude higher than necessary to avulse his liver from the falciparous ligament and therefore rip out its blood supply, rupture his spleen and probably rupture a portion of his heart, enclosed in a fibrous sac, causing tamponade - sealing off the inflow to the heart with static pressure.

We are currently ventilating a man who popped a hole in his lung simply by falling (drunk) from his standing height onto a three-foot bollard.

Deccelaration injuries are not so spectacular to look at from the outside, but cause nasty neck problems and minor problems like tearing the thoracic aorta apart.

meb58, this was undoubtedly very unpleasant to witness. Your description is telling. I would advise you to take some time to work out how you feel about this, and then if you're still having intrusive thoughts, nightmares and so on, speak to someone in due course. Nothing to be done for this chap, so if anyone feels like they could have done something, tell them it was all done and dusted, and not to feel guilty.

### #15 mariner

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Posted 16 November 2009 - 08:24

As I look around the office I see one ex bentley, two ex lotus, two ex holden, two ex ford of europe one ex ford usa and one ex mitsubishi and one ex subaru. FWIW I worked on a holden project before I came here. So there aren't many secrets.

There isn't much difference in complexity of the Euro/Australian vs USA crash. The big difference of course is that USA crash is no seatbelts, so you need a completely different airbag and calibration. I'd guess there wasn't much in it structure wise. Back in the day we did have different structures because of the different bumpers due to the Federal low speed crash requirement, but I don't think the differences were big, just the bumper bar. Actually the legal requirements are pretty easy, NCAP is the bugger, and entirely controls the crash development program.

Sorry to be dumb but why is NCAP such a driver of the crash programme?

### #16 Greg Locock

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Posted 17 November 2009 - 04:09

Almost any legal car or truck gets an NCAP rating of 2 stars, whereas to get 5 stars takes a lot of detail work, and some specified technology (they now include ESC as a qualifier for 5 stars). I use dto be a cynic about NCAP, but there is agreat youtube video of an old and new Espace crashing into each other - the new one is MUCH better.

### #17 gruntguru

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Posted 17 November 2009 - 09:48

Sorry to be dumb but why is NCAP such a driver of the crash programme?

### #18 mariner

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Posted 17 November 2009 - 11:56

1) I know that some of NCAP is non pure crash test related ( e.g pedestrian safety which is I think also now an EU law). This is leading to higher nose designs or explosive charges if you want a low sports nose like Jaguar. Also there are some other "nice to haves " that get NCAP points. However are the actual crash test requirements as the car hits the barrier etc. for NCAP now more severe than the US requirements?

2) If the answer to 1) is yes then does one conclude that European cars ( which realistically need 4 NCAP stars or above to sell well ) are now safer than US bulit cars. This would suggest the possibilty of a whole new wave of lawsuits in the USA from lawyers who will argue " failure of duty " by a mfr. who builds a car just for the US when they also build similar cars in Europe which met the "tougher" NCAP tests.

### #19 meb58

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Posted 17 November 2009 - 20:14

alexbiker,

I'm fine, but I did have to walk away from the scene for a while...there are no words. I was actually quite amazed by how well the folks working on this chap coped...obviously professionals.

meb58, this was undoubtedly very unpleasant to witness. Your description is telling. I would advise you to take some time to work out how you feel about this, and then if you're still having intrusive thoughts, nightmares and so on, speak to someone in due course. Nothing to be done for this chap, so if anyone feels like they could have done something, tell them it was all done and dusted, and not to feel guilty.
[/quote]

Mariner,

I've always been curious about how 'failure of duty' is engaged...in this example it would seem to be very complex issue...being judged with a double edge sword is fundamentally unfair...perhaps this is a poor analogy?

### #20 Greg Locock

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Posted 18 November 2009 - 00:41

1) I know that some of NCAP is non pure crash test related ( e.g pedestrian safety which is I think also now an EU law). This is leading to higher nose designs or explosive charges if you want a low sports nose like Jaguar. Also there are some other "nice to haves " that get NCAP points. However are the actual crash test requirements as the car hits the barrier etc. for NCAP now more severe than the US requirements?

2) If the answer to 1) is yes then does one conclude that European cars ( which realistically need 4 NCAP stars or above to sell well ) are now safer than US bulit cars. This would suggest the possibilty of a whole new wave of lawsuits in the USA from lawyers who will argue " failure of duty " by a mfr. who builds a car just for the US when they also build similar cars in Europe which met the "tougher" NCAP tests.

1) yes 5 * crash rating greatly exceeds US minimum

2) don't know if anyone downgrades the actual structure, it seems unlikely. The buyer is assumed to make an informed choice when selecting a vehicle, if they want a cheap car with fewer stars that is up to them. I vaguely remember a comment from a senior VP that passive crash was esssentially done and over, the pressure to reduce weight will force active safety, which very rapidly becomes robot drivers.

### #21 McGuire

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Posted 30 November 2009 - 23:26

The truck driver made the only correct decision in the above case. Like all drivers, he is charged with maintaining contol of his vehicle, and when he lets the vehicle roll when anticipating an impact he surrenders control of his vehicle and abdicates his responsibility. Hence all the issues with legal and insurance liabilities if a driver admits to doing so, as related above, but the very real basis for them is a moral responsibility. You are morally responsible for the control of your vehicle to the extent of your abilities. When one vehicle is struck by another vehicle from behind, the first vehicle becomes an unguided missile.

I don't know anything about the geographical surroundings of this crash, but we are informed it was on a grade and meanwhile, we have no reason to assume there were no other vehicles and people in the truck's path, including pedestrians. Add to all this that when a truck is driven over a curb, culvert, or other feature, it can easily overturn. Fact of the matter is it is difficult if not impossible to predict what a 8,000 lb truck will do when pounded from behind at 45 mph with nothing restraining it. Letting the vehicle roll in a rear impact is one of those things that sounds like a good idea in theory or in perfect hindsight, especially on a message board or in pub conversation, but in practice it's a bad idea.

### #22 Greg Locock

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Posted 01 December 2009 - 00:10

I don't know anything about the geographical surroundings of this crash, but we are informed it was on a grade and meanwhile, we have no reason to assume there were no other vehicles and people in the truck's path, including pedestrians. Add to all this that when a truck is driven over a curb, culvert, or other feature, it can easily overturn. Fact of the matter is it is difficult if not impossible to predict what a 8,000 lb truck will do when pounded from behind at 45 mph with nothing restraining it. Letting the vehicle roll in a rear impact is one of those things that sounds like a good idea in theory or in perfect hindsight, especially on a message board or in pub conversation, but in practice it's a bad idea.

The first defensive driving course I did stressed keeping an eye on your rear view mirror when stopped at lights, in gear, and prepared to pull away if a rear end shunt looks likely.

Oddly I was in a car a year later when exactly that happened, and our driver accelerated around the truck in front as the one behind hit us. We got away with a bent floorpan and doors that wouldn't close, instead of being squished between two trucks.

### #23 McGuire

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Posted 01 December 2009 - 00:50

Very seldom will the driver of a stopped car have time to get out of the way of an impending rear-end impact, let alone accurately assess if the path is clear in front in order to zoom out of the way. At the instant you hear tires squealing behind you, that generally means that someone was traveling too fast while not paying attention, and meanwhile, not even Superman can competently gauge the speed of an oncoming vehicle when viewed in frontal aspect. Also meanwhile, once one set of tires start squealing, other cars on the scene often begin attempting their own fancy manuevers. In the greatest number of cases there is barely time to react, and the correct reaction is to stay on the brakes.

### #24 GeorgeTheCar

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Posted 01 December 2009 - 04:15

The last time I got hit in the rear it took all my skill to get stopped and not hit the guy in front of me on a wet, snowy road. I was just assuring myself that I was not going to hit him when I heard the tires sliding behind me. Damn!

### #25 dosco

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Posted 03 December 2009 - 12:53

Very seldom will the driver of a stopped car have time to get out of the way of an impending rear-end impact, let alone accurately assess if the path is clear in front in order to zoom out of the way. At the instant you hear tires squealing behind you, that generally means that someone was traveling too fast while not paying attention, and meanwhile, not even Superman can competently gauge the speed of an oncoming vehicle when viewed in frontal aspect. Also meanwhile, once one set of tires start squealing, other cars on the scene often begin attempting their own fancy manuevers. In the greatest number of cases there is barely time to react, and the correct reaction is to stay on the brakes.

I think the point is to always look in the rearview mirror while braking, not while at a stop. I recall being taught that as well. This has come in handy on a few occasions on the highway where emergency braking on my part has surprised the person following me.

### #26 gruntguru

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Posted 05 December 2009 - 10:09

I think the point is to always look in the rearview mirror while braking, not while at a stop. I recall being taught that as well. This has come in handy on a few occasions on the highway where emergency braking on my part has surprised the person following me.

Agreed. If there is nothing in front of you, rolling forward can avoid the crash or significantly reduce the damage. I have seen the former on a few occasions.

### #27 johnny yuma

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Posted 07 December 2009 - 03:19

Agreed. If there is nothing in front of you, rolling forward can avoid the crash or significantly reduce the damage. I have seen the former on a few occasions.

With ABS braking now in a good percentage of cars,are we seeing people successfully "steering around" accidents,or is the lack of reaction time still stopping this ?
I recall locking up brakes in a very agricultural Toyota Hilux twincab on the outskirts of Kempsey,releasing them momentarily to steer around my "target", then getting back on the right side of the road before the oncoming traffic arrived. I could see and judge this manouvre ,but changing lanes on say a 3 lane interstate would be much more difficult as looking in your mirrors or swinging your head around is not what you feel like doing just after you hit the skids. !!!

No I did not signal my intentions with trafficators !!

Edited by johnny yuma, 07 December 2009 - 03:22.

### #28 Greg Locock

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Posted 07 December 2009 - 04:53

Well done.

It'd be interesting to see the stats but my gut feel is that people still just stand on the anchors and plough into the obstruction, mostly. In multilane traffic the idea of dodging around the car in front actully seems rather a big ask, you'd have to check that nobody was coming up behind you in that lane.