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The Physics Behind Car Crashes
Guinnessy writes "Physics Today has an article on Vehicle Design and the Physics of Traffic Safety. The article analyzes in detail typical crashes experienced between cars, and cars with SUVs'. According to Marc Ross, Deena Patel, and Tom Wenzel, "The evidence is compelling that body-on-frame light trucks cannot safely coexist with passenger cars under existing conditions. That problem is critical because so many light trucks are used nowadays as car substitutes." They suggest some ways in which both cars and SUVs' can be redesigned to improve safety. Meanwhile Detriot News reports on a Pediatrics journal study says that claims that children are no safer in SUVs than cars because of the rollover risks."
I'm reminded of an accident I almost saw several years ago. It was at an intersection where the east/west road had right of way, and the north/south road had a Stop sign. I was in a friend's shop at the time, and we heard a V8 accelerating hard, then a sudden very loud *thud*.
Running outside, we saw from the accident that a 1970s V8 Statesman with a P Plate (here, drivers get P plates to tack on their car for the first few years they're driving on their own) had obviously gone through the stop sign and hit the driver's side of a Prelude driven by an elderly driver. The young guy in the statesman was taken off to hospital, but a rescue team was needed to pull the driver out of the Prelude. Later that night the news had a piece about the accident, saying that the p-plater had caused an accident that killed the elderly guy. Even witnesses at the scene said they heard the V8 go through the intersection far too fast, and hit the prelude.
Then the next night, video shot from inside a building nearby showed the accident - the P-plater had actually stopped at a pedestrian crossing, let the people walk across, then accelerated quickly & noisily... but he was actually moving along the east/west road with right of way. It was the driver in the prelude that had gone through the stop sign at high speed, and the young fellow was just in the wrong place at the wrong time, and hit the driver's side of the prelude hard - both cars went spinning around in an impossible looking way, ending up in a position that looked for all the world like the young fellow had gone through the stop sign, even though in this case the only thing he'd done 'wrong' was make a big ol' noise in first gear. My "obvious" guess at who was in the wrong was completely off.
There's a massive amount of energy in a car collision, more than most people would expect given how much we take moving a tonne or two of steel from one place to another daily.
The newest european cars nowadays come with an extra protection agains collisions with pedestrians: The hood in front of the car is lifted a few inches after 40 or so milliseconds so the pedestrian gets lifted as well and won't get run over by the car but lands on the softer hood and might hit the car glass.
The powertrain generally takes up considerable space in the engine compartment, leaving little room between the engine and the bonnet.
To remedy this, the C6 comes with an active bonnet system as standard that automatically raises the bonnet in the event of pedestrian impact. Thanks to an impact sensor and pyrotechnic mechanism, the bonnet rises 65 mm in 40 milliseconds. A second mechanism maintains the bonnet in its raised position despite the impact and thus absorbs the deformation energy.
Example from Citroen.
Dependency hell? =>
I don't know for the USA, but a chinese SUV is being imported into Europe and it received a 0 rating for safety.
So be careful! If you see one on the road, stay well clear.
I'll do it for cheesy poofs.
People are always going to consider their own selfish personal safety as a purchasing factor when choosing a road vehicle; for many people this is a very significant issue, and is played upon by advertising for autos.
We need to focus on methods of ensuring safety that don't threaten other road users: win-win situations rather than soccer moms driving trucks and declaring "I know I will win in a collision" (vaguely remembered quote from a National Geographic article on SUVs). This can only lead to a sort of arms war where we all end up driving 38 tonne truck rigs....I was particularly scared by the picture of the SUV built on what is effectively a couple of forward facing railroad rails - that's going to hurt if you're hit side on in a little compact by one of those.
The annoying thing is I am sure most of the safety issues can be solved with little cost and by improving social as well as technological aspects of road use, e.g. severely enforcing low speed limits round residential areas. As long as its cool to drive like a bastard people will.
I always like the story about how there were a lot of fatal accidents in early autos because of the bolt protruding in the middle of early steering wheels, head on crashes meant drivers suffering lots of chest damage; while this was then changed to make life safer, it's been pointed out that if there was a big spike compulsorily welded onto the middle of all steering wheels pointing at drivers then everybody would drive a whole lot more carefully and there would be a lot less accidents.....
Funny thing anout SUV's. They really are a hazard. Not only is the center of gravity higher, but they usually have misdesigned suspension (Ford Exploder, Mitsubishi Montero) that actually encourages rolling over, SUV's have higher bumpers, so cars running into them slide under, killing the occupants in the lower car. SUV's use more gas and cause more pollution. A very big problem is roof crush. SUV roofs are notorious for being frail and crushing in a roll over accident, squishing the people inside.
I for one don't like the idea of dying by having my spinal column driven into my skull.
Many of these things of course could be mitigated. There could be a standard lane change test to determine suspension quality, there could be rules on the center of gravity, there could be rules on bumper height (like on regular cars) and there could be rules on pollution, perheps making all SUV's except the kind with frugal modern common rail diesel engines (with particle filters) financially impposible to own/buy.
But this is not the case. Infact, with GM and to some extent Ford in financial trouble (and with all their profits coming from SUV's) the current US administration wil do nothing about the laws, that infact make SUV's above the law.
Right now, SUV's are excempt from current fuel efficiency laws (that are not very good in the first place, mind you), they are excempt from bumper laws (making SUV's lousy and expensive to fix in even the smallest parking lot accident) and there are no laws governing roll-overs (only tests).
With all these problems, I don't see why they even allow these on the road.
The funny thing is, I really like the idea of sitting up high in my car and being able to see further. That is probably the only reason SUV's are so popular. Looks like they could accomplish that in a macho looking vehicle without these problems.
Cross-over anyone?
Some say he is made with ascii, others that he is eyeballed daily by millions. All we know is, he is known as the Sig
And they say there is no free lunch.
Funny thing is, other then the "coolness factor," I do everything I used to do in the SUV with the van, and the van is actually better at it since it carries more. This likely includes more off road travel then most SUV's ever see.
As a firefighter and first responder I can state that there's a big problem with the safety crash test ratings most consumers see. These 4 star and 5 star ratings don't tell the real story at all.
These tests emphasise not just the human safety but also the cost of repair. To some extent, the cost of human repair is the factor added to the vehicle repair to make the rating. Interesting data, but not what most of us care about, and it results in very poor decision making information.
Example: I have seen personally how effective "crumple zones" combined with airbags and safety brackets on hoods which prevent the hood from sliding directly back into the windshield in the case of a head on collision can work. I see completely destroyed cars all the time where the occupants are well protected and suffer only minor injuries. That's because much of the force of impact is used up in the act of crumpling the car. These crumple zones are amazingly effective.
The problem for insurrance companies is that crumple zones and the like TRADE vehicle damage for human damage. The low-speed destruction of bumpers, fenders, hoods, and entire engine compartments mean that these cars are a "total loss" much more frequently.
If you REALLY want to promote SAFETY -- and like me, you could care less about the damage to the vehicle if the humans are better protected -- than we need a safety rating system which ignores all things other than damage to the occupants of the vehicles.
AP
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