Huge study about safety can be misinterpreted by SUV drivers

On Fri, 17 Oct 2003 17:52:34 -0400, Nate Nagel <[email protected]>
wrote:

>P e t e F a g e r l i n wrote:
>
>> On 17 Oct 2003 08:52:47 -0700, [email protected] (Dianelos
>> Georgoudis) wrote:
>>
>>
>>>If you care about your personal safety then, clearly, the best
>>>strategy is not to use a SUV but to use a mid-size or large
passenger
>>>car.
>>
>>
>> I care not only about my safety, but the safety of my family, so I
>> bought a very safe SUV.
>>
>> Go figure.
>>
>
>Obviously, then you *expect* to wreck, as you've apparently traded
>handling for crash safety.

Nah, despite your wish that things were that simplistic, it's not the
case.

My SUV is quite safe and handles quite well.

>What are you doing reading rec.autos.DRIVING then?

Oh, part of it is the amusement derived from reading funny posts like
yours I suppose.

>I got no problem with SUVs, as long as they are used for their
intended
>purpose(s) - i.e. hauling stuff, towing, off-roading. But for
commuting
>or store running, it's just freaking retarded.

Fortunately Nate doesn't make up the rules.

What a great country, eh?

In article <[email protected]>, Matthew S. Whiting wrote:

> These stats alone tell you next to nothing. It is also well know that
> drivers are involved in accidents in substantially different rates based
> on age. If the large cars are being driven by people in the safer age
> ranges (very likely) and the SUVs are being driven by people in less
> safe age ranges (a good chance), then death rates (which are typically a
> function of accident rates), will be higher for the vehicles driven by
> the class of driver that has higher accident rates.

Large passenger cars come out ahead in every type of post-crash safety
measure I've seen, including those that are not dependent upon driver
demographics. And they were also safer when those who are now old
and drive them were younger and driving them.

This latest report follows the same trends for what must be a couple
decades by now.

On 17 Oct 2003 14:59:03 -0700, [email protected] (C.R. Krieger)
wrote:

>P e t e F a g e r l i n <[email protected]> wrote in message
news:<[email protected]>...
>> On 17 Oct 2003 08:52:47 -0700, [email protected] (Dianelos
>> Georgoudis) wrote:
>>
>> >If you care about your personal safety then, clearly, the best
>> >strategy is not to use a SUV but to use a mid-size or large
passenger
>> >car.
>>
>> I care not only about my safety, but the safety of my family, so I
>> bought a very safe SUV.
>>
>> Go figure.
>
>If you can't understand what's being said in this thread, I'll just
>suggest that you kiss your family goodbye *every* day ...

On the contrary, I understand what is being said (or written) and I
also understand that people have a tendancy to jump to conclusions,
not read the cited links, read the cited links but not grasp the
underlying assumptions and/or data, etc., etc.

It's incredibly common behavior on usenet.

Nate Nagel wrote:
> Matthew S. Whiting wrote:
>
>> Nate Nagel wrote:
>>
>>> Really? I expect that a collision between two SUVs would be more
>>> dangerous to the vehicles' occupants than a collision between, say,
>>> two VW Golfs (Golves?) due to the construction of the various vehicles.
>>
>>
>>
>> Why do you think that? The SUVs have a lot more distance between the
>> drivers and the front of the vehicle meaning that there is more
>> distance over which to decelerate and this means the deceleration
>> forces could be drastically less.
>>
>>
>> Matt
>>
>
> Probably not, as most cars are now unibody and a "real" SUV has a beefy
> full frame. So the car will "crumple" better, unless it's a really
> beefy (i.e. very high speed) smack.
>
> nate
>

Not necessarily. The frames are designed to crumple as well. Probably
the best available indication would be their respective performance in
crash tests. These are imperfect to be sure, but they are about the
best we have at present.


Matt

Matthew S. Whiting wrote:

> Nate Nagel wrote:
>
>> Matthew S. Whiting wrote:
>>
>>> Nate Nagel wrote:
>>>
>>>> Really? I expect that a collision between two SUVs would be more
>>>> dangerous to the vehicles' occupants than a collision between, say,
>>>> two VW Golfs (Golves?) due to the construction of the various vehicles.
>>>
>>>
>>>
>>>
>>> Why do you think that? The SUVs have a lot more distance between the
>>> drivers and the front of the vehicle meaning that there is more
>>> distance over which to decelerate and this means the deceleration
>>> forces could be drastically less.
>>>
>>>
>>> Matt
>>>
>>
>> Probably not, as most cars are now unibody and a "real" SUV has a
>> beefy full frame. So the car will "crumple" better, unless it's a
>> really beefy (i.e. very high speed) smack.
>>
>> nate
>>
>
> Not necessarily. The frames are designed to crumple as well. Probably
> the best available indication would be their respective performance in
> crash tests. These are imperfect to be sure, but they are about the
> best we have at present.
>
>
> Matt
>

Fixed-barrier crash tests, that is. And I agree.

nate

--
remove "horny" from my email address to reply.

Driver fatalities of 5 per *billion* miles ? Even if you do 20K miles for 60
years, that's still a 0.6% chance...
an acceptable risk in a chicken **** society. Cancer on the other hand ...

Dave Milne, Scotland
'99 TJ 4.0 Sahara

"Nate Nagel" <[email protected]> wrote in message
news:[email protected]...
: Really? I expect that a collision between two SUVs would be more
: dangerous to the vehicles' occupants than a collision between, say, two
: VW Golfs (Golves?) due to the construction of the various vehicles.
:
: nate
:
: Mike Romain wrote:
:
: > You are an idiot bud.
: >
: > If everyone drove heavier vehicles, fatalities would go down just as the
: > numbers below indicate.
: >
: > I do note you don't show any numbers for little econo boxes. Why, are
: > they something like 10 fatalities?
: >
: > Mike
: > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
: > 88 Cherokee 235 BFG AT's
: >
: > Dianelos Georgoudis wrote:
: >
: >>Recently (October 14, 2003) the National Highway Traffic Safety
: >>Administration (NHTSA) released a study about vehicle safety and
: >>weight. See:
: >>
: >>http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/pdf/809662.pdf
: >>
: >>As expected, the NHTSA study did find that heavier vehicles are safer
: >>for their occupants when they crash with a lighter vehicle. This is
: >>well known, and many people buy SUVs thinking that their weight gives
: >>them a safety advantage. Some publications stress this fact (for
: >>example one by USA Today is titled "Lighter cars mean more deaths" so
: >>many people who drive SUVs may feel reassured).
: >>
: >>In fact, as far as SUVs go, the NHTSA study could not have been more
: >>unfavorable. Using real world statistics about tens of millions of
: >>vehicles over several years they prove that the overall safety of SUVs
: >>is worse than of lighter passenger cars. One of the reasons is that
: >>SUVs have a much higher tendency to roll over. This means that many
: >>people spend more to buy a SUV, spend more on gas, and also endanger
: >>others, without much any advantage for themselves. The relevant
: >>numbers are:
: >>
: >>Vehicle type Average weight Driver fatalities
: >> (pounds) per billion miles
: >>
: >>Mid-size 4-door car 3,061 5.26
: >>Large 4-door cars 3,596 3.30
: >>Small 4-door SUVs 3,147 5.68
: >>Mid-size 4-door SUVs 4,022 6.73
: >>Large 4-door SUVs 5,141 3.79
: >>
: >>So it is more probable that you will be killed in a small or mid-size
: >>SUV than in a mid-size car that weights less. Only large SUVs are
: >>safer for their drivers than mid-size cars, but they are less safe
: >>than large cars, even though large SUVs are 1,500 pounds heavier!
: >>
: >>These are amazing numbers. The prorated figures, which take into
: >>account the fatalities in other vehicles involved, are, as expected,
: >>even worse.
: >>
: >>The study does show that SUVs are safer than small and very small
: >>cars, which have a disadvantage only because there are so many much
: >>heavier vehicles around. Very few people who end up buying a SUV were
: >>thinking of maybe buying a small or very small car, so this advantage
: >>is irrelevant. Pound for pound SUVs are always less safe for their
: >>passengers.
: >>
: >>Even when comparing SUVs only, more weight is not always better.
: >>Significantly, small SUVs are safer for their drivers than mid-size
: >>SUVs, even though the latter weight 900 pounds more. I suppose small
: >>SUVs are more car-like and therefore avoid some of the safety
: >>disadvantages of the SUV design.
: >>
: >>If you care about your personal safety then, clearly, the best
: >>strategy is not to use a SUV but to use a mid-size or large passenger
: >>car.
: >>
: >>Of course, the safest strategy for society would be to put an upper
: >>limit to the weight of passenger cars: then we all would drive safer,
: >>spend less money on cars, spend less on gas, protect others, protect
: >>the environment, and be less dependent on unstable oil-producing
: >>countries. Limiting the weight of vehicles is a
: >>win-win-win-win-win-win proposition. Vehicles that have to be heavy
: >>(such as trucks, heavy duty off-roaders, buses, etc) should have their
: >>top speed electronically limited to low levels as to not endanger
: >>other vehicles on the asphalt.
:
:
: --
: remove "horny" from my email address to reply.
:

Dianelos Georgoudis wrote:
>
> ...Of course, the safest strategy for society would be to put an upper
> limit to the weight of passenger cars: then we all would drive safer,
> spend less money on cars, spend less on gas, protect others, protect
> the environment, and be less dependent on unstable oil-producing
> countries. Limiting the weight of vehicles is a
> win-win-win-win-win-win proposition.

Hmmm - that would really inconvenience people like Babs Streisand who
goes shopping in a motor home (not just an SUV for "special" progressive
people) so that she won't have to use public restrooms.

My guess is that you're posting this to several newsgroups as some trial
balloon for a political think-tank. Report back to them that they suck.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")


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P e t e F a g e r l i n wrote:

> On Fri, 17 Oct 2003 17:52:34 -0400, Nate Nagel <[email protected]>
> wrote:
>
>
>>P e t e F a g e r l i n wrote:
>>
>>
>>>On 17 Oct 2003 08:52:47 -0700, [email protected] (Dianelos
>>>Georgoudis) wrote:
>>>
>>>
>>>
>>>>If you care about your personal safety then, clearly, the best
>>>>strategy is not to use a SUV but to use a mid-size or large
>
> passenger
>
>>>>car.
>>>
>>>
>>>I care not only about my safety, but the safety of my family, so I
>>>bought a very safe SUV.
>>>
>>>Go figure.
>>>
>>
>>Obviously, then you *expect* to wreck, as you've apparently traded
>>handling for crash safety.
>
>
> Nah, despite your wish that things were that simplistic, it's not the
> case.

yes, actually, it is.

>
> My SUV is quite safe and handles quite well.
>

BWAHAHAHAHAHAHAHAHAHAHAHA!

>
>>What are you doing reading rec.autos.DRIVING then?
>
>
> Oh, part of it is the amusement derived from reading funny posts like
> yours I suppose.
>
>
>>I got no problem with SUVs, as long as they are used for their
>
> intended
>
>>purpose(s) - i.e. hauling stuff, towing, off-roading. But for
>
> commuting
>
>>or store running, it's just freaking retarded.
>
>
> Fortunately Nate doesn't make up the rules.
>
> What a great country, eh?
>

To paraphrase, I'll fight to the death to defend your right to make an
ass out of yourself in public. That won't stop me from laughing at you
though.

nate


--
remove "horny" from my email address to reply.

"Robert A. Matern" wrote:
>
> ...Politically motivated propaganda isn't just bad science, it's USELESS as
> well.

Actually, if you're sending up trial balloons to see how gullible,
stupid, or ready for the next legislative step in your political agenda
the public is, it could prove useful to a particular political movement,
party, presidential candidate, etc.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")


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Brent P wrote:
>
> Large passenger cars come out ahead in every type of post-crash safety
> measure I've seen, including those that are not dependent upon driver
> demographics. And they were also safer when those who are now old
> and drive them were younger and driving them.

I'm curious: Does this stuff scale linearly? By that, I mean, in two
otherwise identical two-vehicle crashes, one crash comprised of, say a
vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
and the second crash with the two vehicles exactly twice (or apply any
ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
other crash, will the outcome statistically be the same for
corresponding drivers and passengers of both cars in the two different
accidents.

Another way of asking this is: If everyone in the nation became
convinced that bigger is better and got rid of their existing vehicle
and bought a vehicle that weighed 50% again as much as their previous
vehicle, would the safety statistics change for multiple vehicle
accidents (involving the now 50% heavier-across-the-board-vehicles), or
would they stay the same?

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")


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Bill Putney wrote:

>
> Brent P wrote:
>
>>Large passenger cars come out ahead in every type of post-crash safety
>>measure I've seen, including those that are not dependent upon driver
>>demographics. And they were also safer when those who are now old
>>and drive them were younger and driving them.
>
>
> I'm curious: Does this stuff scale linearly? By that, I mean, in two
> otherwise identical two-vehicle crashes, one crash comprised of, say a
> vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
> and the second crash with the two vehicles exactly twice (or apply any
> ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
> other crash, will the outcome statistically be the same for
> corresponding drivers and passengers of both cars in the two different
> accidents.
>
> Another way of asking this is: If everyone in the nation became
> convinced that bigger is better and got rid of their existing vehicle
> and bought a vehicle that weighed 50% again as much as their previous
> vehicle, would the safety statistics change for multiple vehicle
> accidents (involving the now 50% heavier-across-the-board-vehicles), or
> would they stay the same?
>

Basically, yes. An auto crash is fairly inelastic, the safety of the
vehicle occupants will primarily depend on how progressively the
vehicles crush. The amount of energy dissipated will increase
(dramatically) but the end result will be the same. Since energy
increases linearly with increased mass, it ought to scale fairly roughly
as you describe it.

This is, of course, a fairly simplistic explanation and the crash
performance characteristics of the vehicles will be the primary factor
in whether the occupants walk away or not. A head-on collision between
two identical vehicles is essentially the same thing as a head-on crash
into an immovable wall at the same speed; so crash test performance is
the best gauge of safety in your scenario.

nate

--
remove "horny" from my email address to reply.

Brent P wrote:
> In article <[email protected]>, Kevin wrote:
>
>
>>Heaver is better. Take a large SUV, spend a few bucks and put in a roll
>>cage, fire bottle system, and 5 point belts and you will be as close to
>>bullet proof as you can get.
>
>
> The same could be said of practically any motor vehicle, even a geo
> metro.
>
>
Yes but with the metro you would not have the extra weight which
generates more momentum

Nate Nagel wrote:
>
> Bill Putney wrote:
>
> > ... I'm curious: Does this stuff scale linearly? By that, I mean, in two
> > otherwise identical two-vehicle crashes, one crash comprised of, say a
> > vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
> > and the second crash with the two vehicles exactly twice (or apply any
> > ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
> > other crash, will the outcome statistically be the same for
> > corresponding drivers and passengers of both cars in the two different
> > accidents.
> >
> > Another way of asking this is: If everyone in the nation became
> > convinced that bigger is better and got rid of their existing vehicle
> > and bought a vehicle that weighed 50% again as much as their previous
> > vehicle, would the safety statistics change for multiple vehicle
> > accidents (involving the now 50% heavier-across-the-board-vehicles), or
> > would they stay the same?
> >
>
> Basically, yes. An auto crash is fairly inelastic, the safety of the
> vehicle occupants will primarily depend on how progressively the
> vehicles crush. The amount of energy dissipated will increase
> (dramatically) but the end result will be the same. Since energy
> increases linearly with increased mass, it ought to scale fairly roughly
> as you describe it.
>
> This is, of course, a fairly simplistic explanation and the crash
> performance characteristics of the vehicles will be the primary factor
> in whether the occupants walk away or not. A head-on collision between
> two identical vehicles is essentially the same thing as a head-on crash
> into an immovable wall at the same speed; so crash test performance is
> the best gauge of safety in your scenario.

Thanks for the reply.

On the "two identical vehicles head-on = one vehicle into an immovable
wall" thing, it seems self-evident that you could also extend that
analogy and say that a heavier vehicle and a lighter vehicle head-on
would be equivalent to the lighter vehicle hitting a wall that is moving
at some advancing speed (i.e., more damage than head-on into a
same-weight vehicle), and the heavier vehicle hitting a wall that is
receding at some speed (i.e., less damage than head-on into a
same-weight vehicle)

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")


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The results aren't linear, but it's safe to say that even with enhanced
safety design, a 2000 lb vehicle won't fare well when hit by something with
twice as much mass. There's a limit on what can be achieved with design,
simply a matter of physics, no matter what the greens & safety mavens want
you to believe.
Fact is, many of these small cars aren't even safe in single car accidents.

When I worked for VWoA I got close enough to the liability side of the
business to realize one of the industry's dirty little secrets was simply
"small cars kill". Bill Clinton'e NHTSA released a report in 2000 that
concluded the near-mandated downsizing of vehicles through the 80's & 90's
had resulted in the unnecessary deaths of over 16,000 people. The study
concluded the savings in fuel economy over the same period have more to do
with improved engine and systems efficiency than did the reduction in
average vehicle weight.

All I know is, no kid of mine would be sent off to college in a Dodge Neon
or other such death-trap!

Greens often try to muddy the water by citing European studies that show a
similar fatality rate for their small cars as out larger ones. (I'm
surprised wasn't cited in the report,) Comparisons to European statistics
are not valid, because they drive far fewer miles than North Americans and
there is far less disparity in vehicle sizes on European roads, that is,
they drive a lot more small cars than we do.

The whole buzz about SUV rollovers is a smokescreen to try & get people
scared enough not to buy them. It's a hidden agenda by the greens, who 1)
worry about fuel consumption, and 2) want to ban off roading and fear that
the more people have off road capable vehicles they more they'll use them.
(The latter point was confirmed to me a number of years ago by a Sierra Club
official.) Roll overs represent only around 2.5% of all accidents, and have
more to do with idiotic driving than design.
A few years ago the Corvette had the highest rollover rate per miles driven
than any other vehicle. Why? Idiots behind the wheel!





"Bill Putney" <[email protected]> wrote in message
news:[email protected]...
>
>
> Brent P wrote:
> >
> > Large passenger cars come out ahead in every type of post-crash safety
> > measure I've seen, including those that are not dependent upon driver
> > demographics. And they were also safer when those who are now old
> > and drive them were younger and driving them.
>
> I'm curious: Does this stuff scale linearly? By that, I mean, in two
> otherwise identical two-vehicle crashes, one crash comprised of, say a
> vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
> and the second crash with the two vehicles exactly twice (or apply any
> ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
> other crash, will the outcome statistically be the same for
> corresponding drivers and passengers of both cars in the two different
> accidents.
>
> Another way of asking this is: If everyone in the nation became
> convinced that bigger is better and got rid of their existing vehicle
> and bought a vehicle that weighed 50% again as much as their previous
> vehicle, would the safety statistics change for multiple vehicle
> accidents (involving the now 50% heavier-across-the-board-vehicles), or
> would they stay the same?
>
> Bill Putney
> (to reply by e-mail, replace the last letter of the alphabet in my
> address with "x")
>
>
> -----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
> http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
> -----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Kevin wrote:

> Brent P wrote:
>
>> In article <[email protected]>, Kevin
>> wrote:
>>
>>
>>> Heaver is better. Take a large SUV, spend a few bucks and put in a
>>> roll cage, fire bottle system, and 5 point belts and you will be as
>>> close to bullet proof as you can get.
>>
>>
>>
>> The same could be said of practically any motor vehicle, even a geo
>> metro.
>>
>>
>
> Yes but with the metro you would not have the extra weight which
> generates more momentum
>

Only helps you if you collide with another vehicle. Does exactly squat
when you hit something immovable, or significantly larger than you (like
a semi)

I'll take my cars light and nimble, thanks, so I don't wreck at all.

nate

--
remove "horny" from my email address to reply.

Dave Milne wrote:
> Driver fatalities of 5 per *billion* miles ? Even if you do 20K miles for 60
> years, that's still a 0.6% chance...
> an acceptable risk in a chicken **** society. Cancer on the other hand ...

Yes, I was wondering about the units as well. I didn't load the file as
it is 3.1MB which takes some time on a dial-up line, but I wonder if
that isn't million miles rather than billion miles.


Matt

Bill Putney wrote:

>
> Nate Nagel wrote:
>
>>Bill Putney wrote:
>>
>>
>>>... I'm curious: Does this stuff scale linearly? By that, I mean, in two
>>>otherwise identical two-vehicle crashes, one crash comprised of, say a
>>>vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
>>>and the second crash with the two vehicles exactly twice (or apply any
>>>ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
>>>other crash, will the outcome statistically be the same for
>>>corresponding drivers and passengers of both cars in the two different
>>>accidents.
>>>
>>>Another way of asking this is: If everyone in the nation became
>>>convinced that bigger is better and got rid of their existing vehicle
>>>and bought a vehicle that weighed 50% again as much as their previous
>>>vehicle, would the safety statistics change for multiple vehicle
>>>accidents (involving the now 50% heavier-across-the-board-vehicles), or
>>>would they stay the same?
>>>
>>
>>Basically, yes. An auto crash is fairly inelastic, the safety of the
>>vehicle occupants will primarily depend on how progressively the
>>vehicles crush. The amount of energy dissipated will increase
>>(dramatically) but the end result will be the same. Since energy
>>increases linearly with increased mass, it ought to scale fairly roughly
>>as you describe it.
>>
>>This is, of course, a fairly simplistic explanation and the crash
>>performance characteristics of the vehicles will be the primary factor
>>in whether the occupants walk away or not. A head-on collision between
>>two identical vehicles is essentially the same thing as a head-on crash
>>into an immovable wall at the same speed; so crash test performance is
>>the best gauge of safety in your scenario.
>
>
> Thanks for the reply.
>
> On the "two identical vehicles head-on = one vehicle into an immovable
> wall" thing, it seems self-evident that you could also extend that
> analogy and say that a heavier vehicle and a lighter vehicle head-on
> would be equivalent to the lighter vehicle hitting a wall that is moving
> at some advancing speed (i.e., more damage than head-on into a
> same-weight vehicle), and the heavier vehicle hitting a wall that is
> receding at some speed (i.e., less damage than head-on into a
> same-weight vehicle)
>

That's about right, assuming that it's a true head on collision.
Another way to look at it is to consider the point where the bumpers of
the vehicles meet - you can add up the vectors and see which vehicle is
going to get pushed back, and how quickly. (again, collisions - at
least head on ones - are fairly inelastic, so the point of impact can be
considered as a new point where you can sum the vectors and determine
where that point will go.) Or yet another way to look at it would be to
calculate a new equivalent speed of crashing into a stationary wall.
However, if one vehicle crumples progressively and one stays fairly
rigid that will throw off your calcs and occupants of *both* vehicles
will actually fare less well than when both vehicles crush in a
progressive manner.

nate

--
remove "horny" from my email address to reply.

Bill Putney wrote:
>
> Dianelos Georgoudis wrote:
>
>>...Of course, the safest strategy for society would be to put an upper
>>limit to the weight of passenger cars: then we all would drive safer,
>>spend less money on cars, spend less on gas, protect others, protect
>>the environment, and be less dependent on unstable oil-producing
>>countries. Limiting the weight of vehicles is a
>>win-win-win-win-win-win proposition.
>
>
> Hmmm - that would really inconvenience people like Babs Streisand who
> goes shopping in a motor home (not just an SUV for "special" progressive
> people) so that she won't have to use public restrooms.

That is good to hear. I'd hate to think that someone of Streisand's ilk
was out contaminating public restrooms...

Matt

Bill Putney wrote:
>
> Brent P wrote:
>
>>Large passenger cars come out ahead in every type of post-crash safety
>>measure I've seen, including those that are not dependent upon driver
>>demographics. And they were also safer when those who are now old
>>and drive them were younger and driving them.
>
>
> I'm curious: Does this stuff scale linearly? By that, I mean, in two
> otherwise identical two-vehicle crashes, one crash comprised of, say a
> vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
> and the second crash with the two vehicles exactly twice (or apply any
> ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
> other crash, will the outcome statistically be the same for
> corresponding drivers and passengers of both cars in the two different
> accidents.

I may be missing a subtlety, but it should scale linearly as the
momentum scales linearly with mass.


> Another way of asking this is: If everyone in the nation became
> convinced that bigger is better and got rid of their existing vehicle
> and bought a vehicle that weighed 50% again as much as their previous
> vehicle, would the safety statistics change for multiple vehicle
> accidents (involving the now 50% heavier-across-the-board-vehicles), or
> would they stay the same?

I believe the stats would remain about the same, or improve a little as
some crashes are against moveable objects (telephone poles, sign posts,
etc.) and they would yield more readily to heavier vehicles. Obviously,
hitting a bridge abutment wouldn't be much affected by having a heavier
vehicle!


Matt

Bill Putney wrote:
>
> Nate Nagel wrote:
>
>>Bill Putney wrote:
>>
>>
>>>... I'm curious: Does this stuff scale linearly? By that, I mean, in two
>>>otherwise identical two-vehicle crashes, one crash comprised of, say a
>>>vehicle that weighs 2000 pounds and the other vehicle at 3500 pounds,
>>>and the second crash with the two vehicles exactly twice (or apply any
>>>ratio you want) as heavy (i.e., 4000 pounds and 7000 pounds as in the
>>>other crash, will the outcome statistically be the same for
>>>corresponding drivers and passengers of both cars in the two different
>>>accidents.
>>>
>>>Another way of asking this is: If everyone in the nation became
>>>convinced that bigger is better and got rid of their existing vehicle
>>>and bought a vehicle that weighed 50% again as much as their previous
>>>vehicle, would the safety statistics change for multiple vehicle
>>>accidents (involving the now 50% heavier-across-the-board-vehicles), or
>>>would they stay the same?
>>>
>>
>>Basically, yes. An auto crash is fairly inelastic, the safety of the
>>vehicle occupants will primarily depend on how progressively the
>>vehicles crush. The amount of energy dissipated will increase
>>(dramatically) but the end result will be the same. Since energy
>>increases linearly with increased mass, it ought to scale fairly roughly
>>as you describe it.
>>
>>This is, of course, a fairly simplistic explanation and the crash
>>performance characteristics of the vehicles will be the primary factor
>>in whether the occupants walk away or not. A head-on collision between
>>two identical vehicles is essentially the same thing as a head-on crash
>>into an immovable wall at the same speed; so crash test performance is
>>the best gauge of safety in your scenario.
>
>
> Thanks for the reply.
>
> On the "two identical vehicles head-on = one vehicle into an immovable
> wall" thing, it seems self-evident that you could also extend that
> analogy and say that a heavier vehicle and a lighter vehicle head-on
> would be equivalent to the lighter vehicle hitting a wall that is moving
> at some advancing speed (i.e., more damage than head-on into a
> same-weight vehicle), and the heavier vehicle hitting a wall that is
> receding at some speed (i.e., less damage than head-on into a
> same-weight vehicle)

Yes, I believe that is correct. The speed of the advancing wall would
need to be equal to the speed of the combined wreckage of the two
vehicles, assuming they are both fused together during the crash. This
would result in the same total change in velocity for the vehicles -
from a high positive speed to a lower positive speed for the heavy
vehicle and from a high positive speed to a low negative speed for the
lighter vehicle. The acceleration experienced is equal to the change in
velocity and thus should be the same whether you hit a heavier vehicle
or a wall moving toward you assuming that the speed after impact is the
same in both cases.

Matt