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A Weighty Safety Matter

Posted March 29, 2008 8:26 AM

Conventional wisdom says that lighter motor vehicles are intrinsically less safe than those with greater mass. This myth has hampered efforts to improve both fuel economy and emission controls. Recent research demonstrates that automotive engineers can design lighter-weight, lower-mass cars and trucks with better fuel economy that are just as safe as some contemporary counterparts. Intelligent design can overcome safety risks imparted by lower mass in certain accident scenarios, and a 10% reduction in car mass translates into a 3-8% gain in fuel economy. Can engineers give equal weight to mass, safety, and fuel economy?

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#1

Re: A Weighty Safety Matter

03/29/2008 5:09 PM

It says, in certain accident scenarios.

That does not include a light car head on with a heavy car. In fact it does not include any accident between a light car and a heavy car.

Neither does it mean you can drive your "safe" light car in the barrier at 50mph, they tried that with a smart car and a A class Mercedes and it made a mess of things. They also compared it with a 10 year old Vauxhall Nova and decided that you would be just as dead.

No matter how well the car is build, your body cannot withstand certain forces, period.

When are they going to learn that faking safety in cars is always going to produce the opposite effect as people with a false sense of security will take larger risks?

If I could afford it I would drive a Kenworth or a Mack, people only die in one of those when they collide with trains or drive of mountains.


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#10
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Re: A Weighty Safety Matter

03/30/2008 8:37 PM

More truckies die than any one else proportionally in accidents. The typical accident is a rollover (often single vehicle).

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#11
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Re: A Weighty Safety Matter

03/30/2008 9:47 PM

Emjay4119,

Oh your truckie mortality rate is far and away different than US vehicular accident death rates. Annually trucks are involved in about 4700 fatality accidents. The accidents involving trucks in which the trucker dies is less than 800. The number of fatality accidents total cars and trucks is about 49000. So here truckies are an extreme minority in annual fatality rates.

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#12
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Re: A Weighty Safety Matter

03/30/2008 9:57 PM

Fair enough, US trucks are smaller and the roads are better. When one rolls though there is no protection and the load often comes through the cab. Double deck cattle Road Trains are especially dangerous. Even a semi has 22 wheels here and a B double 28 - 32 wheels add another 12 for a B triple.

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#13
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Re: A Weighty Safety Matter

03/30/2008 10:54 PM

I have about 4 months experience driving a B train. Quite an occupational experience or life style depending who you talk to.

There are dynamics involved during a roll over that often break a man's back too.

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#23
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Re: A Weighty Safety Matter

03/31/2008 9:50 PM

Good point. Also there are a lot of objects to hit in the distance a truck takes to slide to standstill. Add to that the sheer amount of hours truckies are expected to drive, as well as around the clock operation. Night shift kills.

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#24
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Re: A Weighty Safety Matter

04/01/2008 10:36 AM

Night shift kills.

Got to know your limitations allot is at stake, day shift drivers can't continue into night.

After five hours constant driving everyone should stop walk around, look far then short repetitively for 15 minutes. Driving over is ill fated indeed.

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#16
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Re: A Weighty Safety Matter

03/31/2008 3:15 PM

The answer is not to fall asleep.

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#25
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Re: A Weighty Safety Matter

04/01/2008 8:55 PM

a.k.a. driving smart...

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#18
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Re: A Weighty Safety Matter

03/31/2008 3:51 PM

case491,

Ah yes I've spent many comfortable hours driving a class "8" vehicle while those in lighter modes were experiencing peril. High winds, ice, high winds on ice/snow; I'd much prefer snow to ice but either in a class 8 than the lighter modes.

But you're meaning just the tractor; oh no that's not comfy at all in those conditions or any other actually. A very ungainly type vehicle, oh sure the 11,000lb engine and drive train makes a wonderful low center of gravity but its akin to driving a fork lift backwards a freeway speeds (:, add water and the fun rides begin.

Very bouncy without a loaded trailer and lousy braking distances without the trailer too.

If everyone drove suitable trans...

I prefer a blue bird bus, drive it to a central location then use suitable conveyance, starting with walking, scooter(no motor), bicycle, skates, motorcycle etc.. Though I wimped out and drive a diesel pick up with 1/4" steel plate in bed for stability, it does carry roofing materials better than the scooter.

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#19
In reply to #1

Re: A Weighty Safety Matter

03/31/2008 4:09 PM

In a bit of a hurry, but I'd like to comment that the to ability to avoid a crash has some merit.

Give excellent stopping power and an ability to maneuver with agility, and maintain reasonable acceleration, and as long as one doesn't fall asleep at the wheel, most hazards are avoidable by an alert driver. Most. I've driven various sizes and weights, trucks, motorcycles, cars...if you can't get out of the way you're screwed.

One wreck I couldn't avoid though; had a 1987 Jeep CJ7 with a brush guard. Got stuck on a one-way street with no room to pull over, a large Chevy van coming straight at me, going the wrong direction. I stopped, flashed the lights, beeped the horn, put it in neutral and laid my head to one side of the steering post. The custom van hit me at 35 m.p.h. Totalled out the van. Witnesses said my Jeep and I went up into the air about 5 feet, and landed 15 feet back. Bent the brush guard a tiny bit. Dogtracked a little, had to adjust the rear axle alignment later. Van weighed a lot more than my Jeep. I went back to work afterward. The driver and passenger of the van went to the hospital. (then jail - drunk) Just one scenario - sure, there are contradictions...

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#20
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Re: A Weighty Safety Matter

03/31/2008 4:19 PM

You followed the first order of safety, never out run your guardian angel...

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#21
In reply to #20

Re: A Weighty Safety Matter

03/31/2008 4:22 PM

Reminds me of a piece of lyrics out of a Neil Young song, "an ambulance can only go so fast".

Off course if you need them it is already too late.

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#22
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Re: A Weighty Safety Matter

03/31/2008 5:03 PM

www.qtires.com may improve the ratio with retractable studs

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#2

Re: A Weighty Safety Matter

03/29/2008 11:56 PM

Design and crush zones and all that may not work all that well. The car with less mass gets the worst damage. Keeping the car large while cutting weight can provide more crush space, but the damage to the car will be greater.

When that Peterbilt or Mack run the red light I would rather be in a large heavy car like a Mercedes than in a Kia Rio.

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#3
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Re: A Weighty Safety Matter

03/30/2008 12:04 AM

I'd prefer a higher ground clearance type, rather be pushed around than run over.

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#7
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Re: A Weighty Safety Matter

03/30/2008 12:40 PM

Design can make a huge difference. The Chevy Blazer, a quite heavy mid-size SUV, was the US's most deadly vehicle to the driver for many years. The lighter Infiniti G35 was among the safest : almost 20 times less likely to kill the driver. The Chevy had mediocre crash test results also. The Blazer had very poor active* safety features (bad handling, bad brakes, a propensity for rolling over) as well as poor passive* safety features (ineffective crush zones, no side air bags, etc).

Some studies have done a good job of accounting for driving style. Several sporty cars are at the high (dangerous) end of the spectrum and at least a few of these have less sporty variants that are quite safe. The Nissan Z 35 is similar to the Infiniti G 35 but is one of the deadliest, rather than one of the safest. The Acura RSX is also one of the deadliest, whereas most of the Hondas do well in their weight classes.

In a collision against a barrier, only properly engineered crush space really matters, and small cars can be engineered to have a lot of fore and aft crush space, and uniform crush response (avoiding human-damaging acceleration peaks). Almost all small cars now get 5 star ratings for this reason. The physics of running a car into a barrier, however, are essentially the same as running head into an identical car (i.e., one very small car against another very small car). In a head-on collision with a larger car, a small car's passengers do not fair as well as the five star rating would lead some people to think.

Fortunately, head-on collisions are rare. The Audi A4, which is quite small, is a good example of a well-designed small car that has 1. a much better chance of avoiding the accident altogether -- because of good active safety features, and 2. a good chance of surviving an accident, because of excellent passive features. It is among the top ten least deadly cars you can buy, and actually somewhat safer, statistically, that an E class Mercedes, also in the top ten. The A4 probably has sporty and younger drivers than the E class Merc -- so if there is a driver profile difference, it should favor the Merc, one would think.

But in general, I agree, you are far better off in a Mercedes than a Kia Rio. Statistics bear out your contention: the Merc is near the best, the Kia is near the worst. But the Merc is clearly superbly-engineered, and the Kia is not -- there are loads of small cars almost an order of magnitude less deadly than the Rio. The fairly heavy Firebird and Camaro also are among the most dangerous -- much more dangerous than other sporty cars.

In order, I'd say that driver, engineering, and mass are the determining factors.

* These terms have been widely used, and may seem ambiguous. When the terms originated, the active features were those that actively helped you avoid an accident, or slow your collision speed. The passive features were those things that involved no driver activity -- once you've thrown your hands up and said "here comes the big noise," the passive stuff takes over: crush zones, safety cages, airbags, etc. (Obviously, there is a tremendous amount of activity occurring in a crash.)

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#8
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Re: A Weighty Safety Matter

03/30/2008 2:51 PM

Have you crash tested your pod or not yet?

Not assuming anything here but it seems to have very little room for crash space.

I would like to state here now that I do not like the big cars very much although looking at my responses so far you could argue the opposite. I would like to see the functionality of the vehicle used more as a reason to buy it, not the looks or status that comes with it. Most builder boys don't need a massive pick up with those awful names designed to put the fear of god in bystanders, they are just Jobs with no brain.

If all cars on the road were only the size they needed to be, we would all be a lot safer in a small, properly designed car.

My daily box is a 1 litre VW Polo. Does not need to be any bigger so it is not.

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#15
In reply to #8

Re: A Weighty Safety Matter

03/31/2008 10:14 AM

Have you crash tested your pod or not yet?

Not intentionally. When it was on two wheels, I managed to drop it at least twice, while learning how to drive it. The avatar version will not suffer a real crash test (I hope) but the second prototype: (of which I am planning four copies) will.

The second prototype will have a Side Impact Protection System (patent pending) which provides about 18" of crush space before the side door beams are contacted. In any typical car, the side impact beams are just under the door skin, so there is no crush space at all (the beams being part of the safety cage, and intended to avoid large deflections). Thus in a side impact, the a typical car accelerates out from under the driver very quickly, and slams into the occupants. The mc2 (its new name) will treat its occupants a little more gently, to offset its mass disadvantage.

The wheelbase will be at least 104" (possibly more, depending on battery configuration) with crush distance to the head and chest region being longer than in most small cars (distance to feet is about the same, but low seating puts the rest of the body further back).

If all cars on the road were only the size they needed to be, we would all be a lot safer in a small, properly designed car.

I could not agree more. Perhaps it is too much to ask, but one would hope that people would think about the potential for their vehicles to kill others, rather than only thinking about their vehicle's ability to protect themselves. SUVs tend to be deadly to others because of frame height mismatch as well as excessive mass, relatively inability to make evasive maneuvers, etc.

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#17
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Re: A Weighty Safety Matter

03/31/2008 3:18 PM

Sounds good and impressive.

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#26
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Re: A Weighty Safety Matter

04/02/2008 5:52 PM

Perhaps it is too much to ask, but one would hope that people would think about the potential for their vehicles to kill others, rather than only thinking about their vehicle's ability to protect themselves. SUVs tend to be deadly to others because of frame height mismatch as well as excessive mass, relatively inability to make evasive maneuvers, etc. Great point! I hadn't thought of that one while arguing for smaller vehicles... Thanks

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#27
In reply to #26

Re: A Weighty Safety Matter

04/03/2008 9:04 AM

Sounds like a great opportunity for auto insurance companies to boost their premiums...

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#28
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Re: A Weighty Safety Matter

04/12/2008 2:14 AM

SUVs tend to be deadly to others because of frame height mismatch as well as excessive mass...Great point! I hadn't thought of that one while arguing for smaller vehicles...

All vehicles need exterior air bags triggered by a proximity device...What do you think?

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#29
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Re: A Weighty Safety Matter

04/12/2008 10:18 AM

All vehicles need exterior air bags triggered by a proximity device...What do you think?

The sensor would have to sense the rate of increasing proximity. Otherwise those bags would go off every time you park too close to the next car, building, fence, bush, etc.

It would take a humdinger of an airbag to significantly reduce the kinetic energy of an entire vehicle at normal highway speeds.

Still, it is an interesting idea!

Dick

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#30
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Re: A Weighty Safety Matter

04/13/2008 12:04 AM

I think I think any amount of deceleration would be beneficial.

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#35
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Re: A Weighty Safety Matter

05/05/2008 2:00 PM

You wrote: The physics of running a car into a barrier, however, are essentially the same as running head into an identical car (i.e., one very small car against another very small car) Are you sure about that? I'd have thought that two objects colliding at speed would generate a lot more physical damage than one of those objects hitting a fixed barrier. Just curious.

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#36
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Re: A Weighty Safety Matter

05/05/2008 11:42 PM

Yes that is correct physics! Have you ever seen the demonstrations with ball bearings hanging on strings? Two identical balls swung from identical heights so they collide, will bounce back form the collision in exactly the same way that a single ball dropped the same way would bounce off a very massive stationary hardened plate.

OR, if the balls are made of soft clay so they don't bounce, the two identical balls swung from identical heights so they collide, will simply splat into each other and stop, just the way a single ball would do hitting the massive plate.

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#37
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Re: A Weighty Safety Matter

05/06/2008 12:20 AM

Are you sure about that?

Yes, that's the way the physics work out. Here's a link that gives a couple ways of looking at it (in addition to dkwarner's answer).

On the other hand, if you are thinking of total damage (to both cars combined) then you are correct that there is twice as much: both cars would appear to have hit a barrier at 35 mph, after they meet head-on.

Looked at in yet another way, if two identical cars, each travelling 35 mph, hit head on, and a third ran into a barrier at 35 mph, all three drivers will have suffered the same accelerations.

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#4

Re: A Weighty Safety Matter

03/30/2008 12:06 AM

If we incorporate reactive exteriors then size my not matter as much.

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#5

Re: A Weighty Safety Matter

03/30/2008 3:57 AM

Two basic things to consider

energy = mass x velocity2 so the bigger you are the harder you fall & the faster you go the worse it gets!

Action and reaction are equal and opposite so the the thing you hit comes off as badly as the thing that hits it.

There is no reason why light weight vehicles cannot be intrinsically safer it is in the design that the means to absorb the energy can be catered for.

Properly engineered light weights would be the best result. Cars are overpowered in many cases. Who really needs a 150KPH car on 120kph roads any way!

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#6
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Re: A Weighty Safety Matter

03/30/2008 5:22 AM

As long as there are SUV's, Range Rovers and Hummers on the road, you are wrong.

You in a small car and me in a Hummer, wanna do the test on live TV? Put your mouth where your money is and say yes!

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#9
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Re: A Weighty Safety Matter

03/30/2008 2:54 PM

Next we'll have lite weight vehicle lanes

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#14

Re: A Weighty Safety Matter

03/31/2008 8:28 AM

I work for Chrysler in their R&D centre in Windsor, Ontario.

Here is a spy photo of the new Chrysler Cordoba, yes we're bringing it back with a vengence. Crappy on gas, but the fine Coooorrrrinthian leather is fantastic to sit in.

Plus NHTSA gave it a 1,000,000 star crash rating.

UFG

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#31

Re: A Weighty Safety Matter

04/30/2008 5:53 AM

I remember an interview a long time ago with the guy who was in charge of GM's safety program from it's beginning; he had introduced all kinds of safety features to the modern motor vehicle, including seat belts, air bags, "soft" dashboards, etcetc. His take was that, every time they did something to make the car safer, people drove worse....... He said that he had reached the view that the most effective safety device would be a bayonet fixed in the middle of the steering wheel, pointy end up! - Perhaps the sensible approach would be to build lighter, more efficient vehicles, (I agree with the views expressed about the quality of design being the most important factor) and make them a bit "scary" to be in?

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#32

Re: A Weighty Safety Matter

05/04/2008 2:57 AM

Safety is of no importance to politicians who make laws. If it were, then the monster SUV's and pickups would be outlawed. Not only due to their excessive weight, but also for excessive height. Their bumpers will hit me in the face in my small car. Plus, they are so high that their headlights shine down directly into the eyes of oncoming drivers, even if there is a concrete barrier between as is found on many freeways.

However, light vehicles can be made safer than they are today as evidenced by race cars with cages that protect the driver. But they would be somewhat less comfortable so the market for them might be limited.

I am considering building my own safety cage to reduce the chances of being permanently paralyzed in an accident. It shouldn't have to be too heavy. What would be the most affordable material and not too heavy? Guess I should examine a race car cage.

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#34
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Re: A Weighty Safety Matter

05/04/2008 6:09 PM

My race car safety cage rant:

In racing, safety cage requirements vary with the sanctioning body, but for many bodies, the specifications are less sophisticated than for the safety cages built into production cars. There is a good article in the SAE magazine this month which shows the structure of the new Volvo XC 60, and the lengths to which they have gone, including making it compatible with the safety structures in other cars. They use about 6 different types of steel as well as aluminum and magnesium to come up with a structure that will absorb a tremendous amount of energy as is crushes, but avoid dangerous deformation of the safety cage itself once that crush space is used up. Race cars are not well-designed for frontal crashes, because frontal crashes so rarely happen in racing. Everyone travels the same direction, and even when a car is spinning, its overall motion remains generally forward.

One reason that race car safety cages are brought up so often in these discussions is that they are easily visible -- and the reason they are so easily visible is because the car has been stripped of all (or never started with) the safety structure of a road car (which is completely hidden in a road car). In most racing rules, there is no requirement for crash testing, and there is no comprehensive requirement for fully-engineered crush (absorption) structures.

The racing crashes that are spectacular and seem dangerous are the ones that last a long time -- and that is exactly what makes them safe: it is quick speed changes, such as from 50 mph to 0 in milliseconds, that are deadly. As a race car spins, and even flips, many of the impacts are only from a car dropping a few feet*. In fact, in some racing rules, the roll bar is only required to support 4 times the weight of the car (if I remember correctly). In contrast, way back in the 60's, Volvo ran an add in which they stacked up 11 Volvos, one atop the other, to demonstrate that their safety cage would support 10 times the weight of the car.

Since then, Volvos have become more and more impressive in this kind of stuff, and other manufacturers have followed suit. (Volvo lead the other manufacturers by 20 years in actively selling safety, and, in my view, is one of the few manufacturers who honestly have built concern for safety into their culture as an overwhelming core value. Others build in safety to avoid lawsuits -- Volvo builds it in because they really care... and, in fact, that care comes largely from the Swedish culture. But Volvo deserves special credit, because Saab has not done as well in terms of developing safety systems or selling people on the value of such systems.)

There is a crash of a Smart Car into a barrier making rounds on the web. The safety cage remains intact, which seems impressive, but is not. Golf balls, every day, are subjected to incredibly high accelerations without any damage whatsoever. Imagine a miniature person inside a hollow golf ball. If you cut the ball open after the collision with the club, all you'd see, stuck to the insides of the ball would be a reddish paste (think bugs on your windshield -- and realize that bugs are many times stronger, relatively to size and mass, than human bodies). The accelerations to which the Smart Car driver would be subjected in the crash video would be unsurvivable. The Smart Car has been tested now in the US, and it is no better than any other small car -- and is worse than most in several respects. Here, in the US, there is no good reason for a car to be as short as a Smart Car. (99% of our parking spaces are made to fit not only average cars but SUVs.) Here, the Smart car is a cute death trap, because it doesn't have enough crush space to compensate for it's very low mass. The safety cage is fine, but it needs more crush space to put it on equal footing with even a small car, let alone a large one.

This is an area, incidentally, in which the five star rating can be misleading. A car crashing into a barrier is equivalent, in the physics involved, to that car crashing head on into an identical car. So it doesn't take any more engineering to make a small car get a five star rating than it does for a large car -- the small car has proportionally less crash energy. For small cars to survive head-on crashes with large cars however, five star ratings are not enough -- they need larger crush zones, and better controlled (more even) accelerations: there should be 6,7, and 8 star ratings for small cars to make them more able to compete with large cars in head-on crashes.

In another video you can see a large Mercedes collide head on with a Smart Car. In the Smart car, which reverses direction and flips over entirely, you can see the golf club effect, where a large mass hits a small mass.

In side impacts, almost all cars lack adequate crush space. So for safety, you would be further ahead to install side air bags: with an intact safety cage (which any modern small car will have) when you are hit from the side, the entire car, cage and all, comes flying at you and smashes into your side. Without airbags, lethal accelerations occur if the intruding car is doing 30 mph or more. The Toyota Yaris, which is not equipped (as standard) with side air bags, did poorly in side impact tests, despite modern engineering. The similar Honda Fit (side bags standard) did well. Shame on Toyota -- it is clearly not that they don't know better -- it's that they don't care enough to erode profit or market position in the interests of safety. I think the market will prove their calculations incorrect: Honda, will, I hope, make a small profit on a ton of cars, and Toyota will make a slightly larger profit on very few cars. Better to make $500 on each of 200,000 cars than $700 on each of 10,000. I suppose Toyota is hoping that the buyers are ill-informed -- unfortunately that's a too-successful strategy.

BTW, while still ranting: I crashed my racing motorcycle at 80 mph, going into a tight turn, many years ago. The only real impact was caused by my butt dropping from seat height, which, with the bike already leaned 45 degrees, was only about 18". Most of that slight impact was easily absorbed by the motorcycle. I slid for about 200 feet, the first 40' on pavement, gradually slowing all the way. My leathers got a little hot, and one glove ground all the way through in a tiny spot where I still have a tiny scar. The bike was still ridable, and I was able to ride it back to the pits. Had this happened on the road, with so many solid objects to hit while I was still moving at 100 feet per second, chances are very high that I would not have survived. So, even with no safety cage whatsoever, I survived what I am told looked pretty spectacular (because because I slid so far, kicking up grass)... and, of course, the very fact that I slid so far is what makes me able to tell the story: I've had scarier rides on roller coasters.

So with race crashes, the very thing that makes them spectacular (their length) is what makes them safe -- it's the track design (with nothing solid to hit straight on) and that fact everybody is alert and going in the same direction that makes most race crashes survivable.

Put race cars in the hands of drunk 16 year olds on public roads to see real carnage.

* For a car to hit the road with a vertical speed of 32 feet per second (21mph -- an easily-survivable collision speed) it would have to fall from 16' -- a height rarely seen in even the most impressive race car flips.

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Anonymous Poster
#38
In reply to #34

Re: A Weighty Safety Matter

05/06/2008 2:33 AM

Excellent answer. Thank You for the information! I learned a lot from your post.

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Anonymous Poster
#39
In reply to #34

Re: A Weighty Safety Matter

05/06/2008 2:39 AM

In case you haven't seen the aptera electric car, check it out: www.aptera.com

There is a video on the website - I think it starts out with a picture of a flower. Play that one to see the car in action.

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Guru

Join Date: Aug 2006
Posts: 4484
Good Answers: 245
#40
In reply to #39

Re: A Weighty Safety Matter

05/06/2008 5:55 PM

Thanks for the link. As it happens, I am aware of the Aptera, and think certain Aspects of it are pretty neat. It will be interesting to see how it does in side impact crash simulations and actual test crashes. I'd expect it to do well in frontal barrier impact tests, and pretty well in head-on crashes, if the weight mismatch is not to high.

My favorite such vehicle is my own (duh!) www.gaiatransport.com. At that site, I promote my own side impact protection system, which is particularly applicable to three wheelers.

There are loads of high efficiency vehicles coming out, and if you go to the Automotive X Prize site you can find links to information on some of the competitors.

Also, the Milner flying car will certainly get your attention -- they are planning to first produce an electric wingless version of the car. (Then... it spins a cucoon... and out comes the winged version )

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Anonymous Poster
#33

Re: A Weighty Safety Matter

05/04/2008 3:12 AM

Wearing a bicycle or rock climbing helmet would help prevent head injuries. A full face motorcycle helmet would really be safe. Put a bike tire in your car that can be seen by others and they'll think you're going bicycling. Secure the tire so it doesn't become a projectile in an accident.

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