The Physics Behind Car Crashes 732
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."
Physics of car crashes aren't intuitive. (Score:5, Interesting)
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.
European car security (Score:5, Interesting)
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. [citroen.com]
Chinese SUV (Score:5, Interesting)
So be careful! If you see one on the road, stay well clear.
Re:Physics of car crashes aren't intuitive. (Score:2, Interesting)
well the best way to drive home just how much energy it takes to move a car is mandantary push starts(and pushing it downhill is cheating).
People will always buy an auto they feel safe in (Score:5, Interesting)
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.....
On SUV safety (Score:5, Interesting)
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?
Re:Physics of car crashes aren't intuitive. (Score:5, Interesting)
Damn Straight.
The Megane was very severely damaged, with the driver and front passenger sustaining some injuries, mainly limited to cuts from glass and severe bruising. The passenger hit her head on a bent bit of A-pillar.
The H2 was *destroyed*. The impact knocked it on its side, and pushed the gearbox and transfer box through the floor and out through the roof. The chassis was split in two from about the middle up to the front crossmember.
I suppose I don't need to draw any pictures of what this did to the four occupants.
Insurance costs could fix this (Score:2, Interesting)
Have you seen their most recent ad? (Score:2, Interesting)
Re:Physics of car crashes aren't intuitive. (Score:2, Interesting)
Re:Wimpifying the SUV's and Trucks is not the answ (Score:3, Interesting)
Re:Physics of car crashes aren't intuitive. (Score:3, Interesting)
On a somewhat related note, i never understood how gay people who want to get married, but can't here in the US (most states) haven't sued the insurance companies. Married men pay a lower rate than unmarried men, but gays don't have this opportunity. Seems like a great way for some lawyer to make money...
Mini vans vs SUV's (Score:5, Interesting)
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.
Re:Insurance costs could fix this (Score:2, Interesting)
Re:what is the definition of "safely" ? (Score:3, Interesting)
Presumably, if the average 51 year old drives as poorly as a person with a BAL of 0.08-0.10, then the average 71 year old would drive comparably to a person with an even higher BAL. If an elderly person has the same driving capabilities as a person with a BAL of 0.15 should the be allowed on the road because they don't have a choice? In fact, they DO have a choice: they could choose not to drive.
Similarly, a person who has slept 1 hour in the last 48 hours is likely to be a terrible driver, comparable to a person with a high BAL. Doesn't this person have a choice to not get behind the wheel of a car? How about a terribly sick individual?
From hearing people in this country talk, you would think driving was a necessity akin to eating, clothing and shelter. Because we treat it as such, we are more afraid of the consequences of taking away drivers licenses than of having dangerous drivers on the road. How many chances does the average DUI offender get before their license is permenantly revoked? How many accidents does an elderly driver have to have before their license is revoked? Too many, if you ask me.
What is the difference between a drunken driver and a driver who is impaired in other ways? Nothing. They are all shitty drivers and they all have a choice: the choice not to get behind the wheel of a car.
Taft
Re:Physics of car crashes aren't intuitive. (Score:4, Interesting)
I saw the result of this last Saturday when there was some freezing rain early in the morning. Driving down Route 80 I counted 14 accidents in the space of about 20 miles. The majority of the vehicles involved were SUVs, and when a car was involved it was usually because an idiot in an SUV had rear-ended them. Worst accident was some large SUV that looked liked it had rolled end-over-end. Couldn't have been more squashed if it had been hit by a train.
The combination of vehicle weight and perceived driver invincibility seems to make SUVs deathtraps in anything other than perfect driving conditions. Ironic, when you think about it.
Crash Ratings don't say what you think (Score:5, Interesting)
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
Re:weight& speed are the big issue here (Score:3, Interesting)
The mass of the vehicles involved is an interesting and significant data point but it's not the whole story. The way the shape of the vehicle changes during a collision is extremely important. The force with which you're whipped around against your various restraints and airbags is important, but none of that matters if the passenger compartment's geometry radically changes while you're sitting in it.
It is easy to see how some big vehicles are not going to be very great in this regard, as rigidity of the passenger compartment can't be a huge priority in their design. The more safety-oriented Euro manufacturers design their cars around the crew compartment but you obviously aren't going to do that with a vehicle designed primarily to haul cargo.
There have been some other morbidly entertaining SUV safety flaws over the last few years. I'm pretty sure one of the Honda SUVs was the first vehicle to ever cut the legs off a steel crash test dummy.
Rollover certainly isn't the only danger, although it sure ain't pretty. Chassis rigidity doesn't tend to scale as the mass of the vehicle increases. Volvo used to show off its wagons in ads with three of them stacked on top of one another. I wouldn't want to sit in a rolled-over Escalade any longer than I absolutely had to...
Size is important. (Score:3, Interesting)
The problem comes down to driver ignorance and stupidity. This, however, isn't something unique to SUV drivers. Around where I live there have been countless idiots crashing into various objects in their beat-up, riced-up small Japanese imports. The city can't do anything to beautify the city without one of these morons coming along and destroying it. They sure do a good job of flipping those cars over too.
That said, mass is a huge factor in determining passenger safety. Of course there are situations where people in a smaller car fare better than in the larger car, but that's the exception.
We have all these crash tests which award the same high marks to a small car that they do to a large car. But these tests are performed under controlled conditions in the kinds of impacts people rarely encounter in real life. These tests are also conducted at relatively low speeds. The kinds of speeds drivers on the road are exposed will completely destroy a car regardless of all the safety features car makers install. And a driver in a large car has one simple advantage: there is more of the car to crash before the impact reaches the driver. I've heard from a few sources that a driver in a small car is up to 13 times more likely to die in a small car compared to a large one.
Of course, if you're driving something as poorly built as that Jiangling nothing will help you, but that's another story. I'm surprised that Europe, with all it's regulations even allows the thing to be sold there. Then again, considering some of the things I've seen on the road there, it's not too surprising. The US is fairly strict. The ride height for the new Golf GTI was raised
How about semis? Redesign them too? (Score:1, Interesting)
Redesign them to be unibody, too? I think not.
So, the lowest common denominator sets the rules? I guess we'll all be driving flimsy 2CVs or Neons.
Buy the biggest, safest car/truck you can afford. Stay alive. Profit.
Re:Physics of car crashes aren't intuitive. (Score:2, Interesting)
Re:weight& speed are the big issue here (Score:2, Interesting)
That being said, If given a choice between my child dying and saving a family of 6 that I don't know, or my child being saved by the death of said family of 6, I'll save my child. It may sound harsh, but that's my kid and my children trump the rest of the planet as far as I'm concerned.
I'm not saying an SUV is safe by any stretch.
When most vehicles on the road were small cars and light trucks and the occasional SUV then the odds were in favor of the SUV that they would be the heavier vehicle involved in a crash and win the war of weight. Now that a large proportion of the vehicles on the road are SUV's you gain almost nothing as the odds are pretty good you're going to tangle with another SUV or full sized truck. The guy/gal in the Kia Rio is going to die.
The biggest danger in an SUV is the high center of gravity. Standard trucks are better in this regard as they tend to have a lower one. Cars win hands down in this area and are typically much harder to flip.
Regardless of the vehicle, flipping and landing on the roof is the biggest danger to the passengers.
And just as an aside, a friend of the family was driving an old mid 80's suburban and was t-boned by a fully loaded gas truck that was doing 45. It was the mother and every kid (all 4 kids) in the suburban, buckled in, and they all walked away with nothing more than strap bruises. replace that suburban with a neon and I'll give you 3 guesses how many would have died.
With all 4 wheels on the ground they are safer than a Corolla.
Re:what is the definition of "safely" ? (Score:3, Interesting)
Ah, but it is akin to eating, clothing, etc... We have evolved into a culture that requires transportation to be employed and to socialize. In the VAST majority of the US it's very difficult if not impossible to acquire food, clothing and shelter without a driver's license. Most non-metropolitan areas don't have good public transportation, and many cities don't either. Sure, the problem would be solved if we all moved to a major city where everything was in walking distance, but that's not practical either.
I think the whole attitude that 'driving is a priviledge' is half of our problem. If safe transportation was viewed as a requirement for modern life some of these decisions could be made more intelligently.
Motorcycles (Score:3, Interesting)
Sort of. The ignition systems, engine designs, suspensions, and brakes of bikes are often more advanced and weight-optimized. However, many bikes still use carbs instead of fuel injection since the pollution standards for bikes are laxer and it's expensive to make a fuel injection system that works well at over 10k RPM.
Furthermore, bikes don't normally last as long as cars (100k miles is a long lifetime for a bike) so maybe their weight optimization has some negative consequences.
That being said, I ride. It's fun, my bike gets 60-65 mpg, I get to use carpool lanes alone, and I can squeeze into gaps in traffic... The downside is of course safety, but I'm willing to accept that risk to some extend.
Cheers,
-b.
Re:Size is important. (Score:3, Interesting)
Bumpers are actually 2.5mph now. 5mph bumpers were more of an consumer economic protection regulation than a safety rule - too many people complained about their cars getting expensively damaged in slow collisions. I think the rule was dropped because car makers lobbied for the right to do stupid things like equipping cars with quick-scratch body-color bumpers.
I *wish* the US had laxer safety standards (or at least accepted the results of Euro crash and emissions tests). That way, we could get nifty vehicles that we're missing out on, like the Land Rover Defender 90, Smart Car, and any number of French cars.
-b.
Re:weight& speed are the big issue here (Score:2, Interesting)
You dont need *expensive* tires. Just really good tires. You don't need to blow megabucks to get decent rubber.
Right off the top of my head I can think of 3 tires which are sub-80 dollars a piece (on 14 or 15" wheels) and are fantastic rubber.