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."
weight& speed are the big issue here (Score:3, Insightful)
Driving fast in an SUV loaded with kids is about as unresponsible as it gets, I see it quite often though...
Re:weight& speed are the big issue here (Score:2, Insightful)
Re:European car security (Score:1, Insightful)
Re:weight& speed are the big issue here (Score:2, Insightful)
Also, from the GP that says "keep your speed down and your vehicle weight down".
I would rather be in a fully loaded 18 wheeler going 100 MPH than in a Honda Prelude sitting still.
Now with the SUVs not being any safer for kids, the same is true with antilock breaks. They are both better at reducing injuries in not so hazardous situations, but both are more likely to kill you in serious situations.
Re:weight& speed are the big issue here (Score:3, Insightful)
It is true for the people in your car probably having less injuries when yours has the largest Mass but the question remains of what is the impact when an SUV hits another SUV? Are you still as safe as hitting a car?
While that is mostly true (Score:3, Insightful)
Re:weight& speed are the big issue here (Score:4, Insightful)
That's not to say that SUVs are safer than normal cars. The rollover risks aren't trivial. Personally I think SUVs should be banned, or at least put into some special category of business only use because of the safety risks they put on other cars. The SUV craze is literally killing more people and making driving for everyone else less safe, and this article proves it.
Re:Physics of car crashes aren't intuitive. (Score:3, Insightful)
As for the mostly males involved in crashes, it's the same statistical nonsense as mostly red cars are involved in crashes. It's simply because there are more males on the road to be driving dangerously. Insurance for me (18yo Male, learning to drive) is phenominal even on a low power car. Fortunately I plan to do a Pass Plus (An extra test for additional road skills) so it should drop, but your comment about subsidising the idiots still holds true even then.
Re:weight& speed are the big issue here (Score:5, Insightful)
Since when? Are you alluding to the misconception that a good driver can stop faster without ABS than an average driver with? With modern ABS this just isnt true anymore, even if you're a rally driver.
And ABS systems let an average driver steer their car in a heavy-braking-potential-skid situation, where the non-abs car will be skidding in an uncontrolled straight line. How many drivers are taught cadence braking these days?
Re:Wimpifying the SUV's and Trucks is not the answ (Score:4, Insightful)
Bigger cars to suffer more parking damage (Score:2, Insightful)
I was waiting outside a supermarket the other week, in a parking slot, and one of these tossers shows up and stops in front of me to let out his passengers before moving into a space. The reason was obvious. His car was too damned big to get the doors open properly when it was between two other cars. As far as I'm concerned he should expect to have his bodywork smacked up by the car doors on either side of him.
I also always make a point of thanking people for waiting on narrow roads where parked cars make it impossible for two cars to pass eachother, unless they're driving something like a VW Touraeg. If it is possible for two normal cars to pass each other and your stupid truck sized car is making it impossible then it's your own fault and you'll get no thanks from me. If you drove a normal car you'd have had no reason to stop.
Re:Well, that settles it then... (Score:2, Insightful)
I find it amusing when the vehicle is blamed rather than the operator.
what is the definition of "safely" ? (Score:5, Insightful)
The author of the study is making the mistake that safety is a boolean, and that things are either safe or unsafe.
In fact, everything is unsafe, to varying degrees. ("Life", in the words of Warren Zevon, "is gonna killa you").
The important thing, when contemplating questions of public policy, is to COMPARE one risk to the next, and make sure that we're making reasonable decisions and tradeoffs.
For example, over the last 10-15 years, a lot of states have dropped the DUI (driving under the influnce) BAC cutoff (blood alcohol content) from 0.1% to 0.08%. Lower is better, right?
Well, as it turns out, having a BAC in the 0.08 - 0.10% range has the same effect on driving ability as (a) having a cold; (b) getting a poor night's sleep; (c) being over the age of 50.
If we're going to make a 0.81% BAC illegal (and punish it with major fines), should we not also have the same punishments for driving while having the sniffles, or while being 51?
The answer is that one behavior gets a penalty because it sounds good, makes politicians look like They're Doing Something(tm) and has moralistic overtones ("get those damn drunks off the road!").
To say that "light trucks cannot safely coexist with passenger cars " is purest nonsense. We've had light trucks coexisting with passenger cars for 70 years, and the fatality rate drops every single year. Sure, if you could snap your fingers and get every pickup truck, minivan, delivery van, and SUV off the road, things would get incrementally safer for the average driver of a passenger car.
I don't know off the top of my head, but is it a level of safety comparable to every passenger car driver making sure that their tires are fully inflated before each trip? Or more, or less?
Absolutist boolean statements like "X can not safety coexist with Y" do not answer questions like this. These statements are public-policy-by-press-release and deserve to be condemned.
Re:I reckon.. (Score:5, Insightful)
Re:People will always buy an auto they feel safe i (Score:5, Insightful)
Of course, the heavier vehicles always create a false sense of security. Trucks and large vehicles are more prone to rollovers, can't stop or swerve easily to avoid trouble, and hit stationary objects with more momentum. But like Homeland Security or MS Windows, it makes you feel safe, so people choose to go with it even if the facts are completely against them.
Really your best defense while driving is to actually use everything you learned in Driver's Ed, or if you don't remember than find books or classes on safe driving. And if there are any teenagers reading this, remember that Driver's Ed is the one class most likely to determine at some point whether you survive a situation. You know, driving at reasonable speeds (somewhere around the speed limit is usually good), slowing down before you take corners, being aware of the drivers around you, good signalling so other drivers are aware of you, etc.
Re:European car security (Score:5, Insightful)
Being a long-term survivor of pedestrianism is one of the best ways to become a cynic of the human condition. It annoys me that my local media have to make a point that "alcohol and drugs were not involved" -- to which I always think, "Great, a clean kill." Running over a pedestrian is the safest way to experience the thrill of murder. Unlikely you'll even get the workhouse if you aren't too blatent about it. But be warned that if you only wing your pedestrian you could be paying off the multi-million dollar lawsuit for the rest of your life under the new bankrupcy rules. So in the end it's smarter not to run over pedestrians, ok?
[Aside from personal experience, I tend to be even more cynical because working in various places and talking about walking to work I have met _three_ secretaries who each had their father killed at a stop sign or stop light pedestrian walk.]
Re:Physics of car crashes aren't intuitive. (Score:5, Insightful)
Not from my point of view... their problem is this: the SUV usually wins. From my meager time in life, I've seen plenty of reckless drivers. Not all of them were teenagers... I've seen my share of reckless soccer moms, businessmen, and delivery drivers. Quite a few of these drive heavier vehicles. I suppose it makes them feel safer, being in a heavier vehicle (which they probably are).
They continue their reckless driving habits, however, now becoming that much more of a threat to the general populace driving smaller cars. They may be more likely to survive, but they're decreasing the chance of survival for everybody else.
Until everybody "wises up", goes out and buys an heavier vehicle... at which point we're right back at square one, with worse gas mileage.
Re:Bigger cars to suffer more parking damage (Score:2, Insightful)
That's assuming... (Score:2, Insightful)
Also, its important to consider deformation fo the passenger "cage" to be almost as important. A lot of light trucks/suv tend to have signficant instrusion into the footwell and "A" pillar in offset front collisions making them less safe than they first appear.
On the other hand, if you have a 5000 pound SUV hitting a 2000 pound minicompact, I don't have to be Newton to figure out the result.
But in reality, most new cars weight closer to 3500 pounds, and most SUV's are probably around 4000, so despite looks, there's less of a difference than it appears. Combine that with the fact that many cars have more sophisticated crash zones than SUVs and far less tendency to roll over, and you get that a car can be far safer than an SUV.
Personally, I'll take my changes in my BMW rather than a Ford Explorer.
Re:On SUV safety (Score:2, Insightful)
Sport = off road
Utility = Carrying or towing capacity
Off road use requires a higher center of gravity to allow clearance over hazards, the ability to cross over ridge crests without scraping the undercarriage, etc.
Carrying capacity and towing capacity requires both additional cubic cargo space, weight and power. SUVs are used for towing boats, trailers, campers, etc., and need these additional characteristics to be successful.
All of this is expensive. A typical SUV starts out at the dealership at over $25K, with most coming in at over $35K once you add the additional towing packages, etc. Many come in at over $45K!
If a family camps, boats, or participates in other off road activities, an SUV is often a necessity. But at that expense, many people can't afford both an SUV and a regular car. So they buy just the SUV, or they can afford just one additonal car, so Hubby drives the lower gas milage car to the more distant workplace, and Soccer Mom drives the SUV around town cause thats all the cars they can afford.
At least in the US, the government doesn't have so much power that they can just ban a particular vehicle without political consequences. Not when it's as popular as the SUV. The recreational lobbies would eat them alive.
It's only a very small minority of folks that just buy an SUV as a status symbol.
Re:Physics of car crashes aren't intuitive. (Score:4, Insightful)
Now I was never a particularly aggressive driver (and the only accident I ever caused was when I reversed into a concrete pillar) but I can safely say that in 19 years of driving I leave a lot more space in front and anticipate other drivers' bad behaviour better than I used to. Hell, when I was 25 in a little 988cc car I used to drive a section of country lane in about half the time that I would risk it now - in a car with 2.5x the power. It's all about testosterone and perceived invincibility.
Re:weight& speed are the big issue here (Score:4, Insightful)
Re:weight& speed are the big issue here (Score:3, Insightful)
But you can't ignore the fact that ABS lets you steer the vehicle in a 'panic braking' situation, and its this abilty to steer (cf skidding in a straight line) that lets people turn too hard and rollover their vehicle.
I'd have thought that the ESP systems that are becoming more commonplace would be able to reduce the problem though.
Having said all that, I still prefer my car with no driver aids.
Re:weight& speed are the big issue here (Score:1, Insightful)
Kudos, you passed HS physics.
But this wasn't the whole point of the article. In fact, most of the article was about what is the best way to get rid of that kinetic energy--especially the kinetic energy in the passenger. For example, seat belts and airbags end up being (surprise, surprise) engineering tradeoffs. The slower the components decelerate the passengers, the lower the stress on the passenger--that is, until it works to slowly to prevent them from smacking into the dash. Oh, not to mention the vast variability in weight and stature (aka mass and lever arm) that a designer would have to envelop in the design.
And what about the mass of the vehicle? Various people have (as astutely as any good HS physics student should) that lower mass lowers the input energy in a crash. HOWEVER, lower mass also means less mass to absorb the input energy in an accident--that means higher stresses in materials, which means greater deformations. Again, the problem is going to be a balancing act. How does the designer reduce mass while retaining the ability to disperse energy? Pun intended, there is a break even point. Can it be improved by material selection? Maybe, but does that increase the cost of manufacturing a car--or disposing of it? These aren't easy questions with obvious answers. Any idiot could get an engineering degree if they were.
Of course, this was all the real discussion of the article.
Carl
Re:On SUV safety (Score:3, Insightful)
Re:Physics of car crashes aren't intuitive. (Score:5, Insightful)
They probably are safer in their huge SUV. Too bad they are not thinking about the people they will murder though. If they were driving a lighter car which would more effectively crumple and absorb impact the people in the other could maybe survive.
I guess it re-inforces the stereotype of the SUV driver as the guy who doesn't give a shit about anybody else except themselves. Don't care about the environment, don't care about foreign oil dependency, don't care about the survival of the other guys in the crash.
Re:Well, that settles it then... (Score:3, Insightful)
And the trucking industry constantly lobbies for greater weights for their trucks. Which cause lots of wear and tear on the roads if nothing else. But now they can't stop as quickly, and they can't get out of their own way on a hill, resulting in mini traffic jams and high speed differentials, which are a dangerous situation.
Re:what is the definition of "safely" ? (Score:3, Insightful)
If we're going to make a 0.81% BAC illegal (and punish it with major fines), should we not also have the same punishments for driving while having the sniffles, or while being 51?
Being convicted of a DUI is a crime in most states. In mine, you get 3 years in prison after the third one. Here is an account of such an unfortunate person:
I've been sentenced for a D.U.I. offense. My 3rd one. When I first came to prison, I had no idea what to expect. Certainly none of this. I'm a tall white male, who unfortunately has a small amount of feminine characteristics. And very shy. These characteristics have got me raped so many times I have no more feelings physically. I have been raped by up to 5 black men and two white men at a time. I've had knifes at my head and throat. I had fought and been beat so hard that I didn't ever think I'd see straight again. One time when I refused to enter a cell, I was brutally attacked by staff and taken to segragation though I had only wanted to prevent the same and worse by not locking up with my cell mate. There is no supervision after lockdown. I was given a conduct report. I explained to the hearing officer what the issue was. He told me that off the record, He suggests I find a man I would/could willingly have sex with to prevent these things from happening. I've requested protective custody only to be denied. It is not available here. He also said there was no where to run to, and it would be best for me to accept things . . . . I probably have AIDS now. I have great difficulty raising food to my mouth from shaking after nightmares or thinking to hard on all this . . . . I've laid down without physical fight to be sodomized. To prevent so much damage in struggles, ripping and tearing. Though in not fighting, it caused my heart and spirit to be raped as well. Something I don't know if I'll ever forgive myself for.
-A letter to Human Rights Watch
Although I thought that the US was bad about their BAC limits, they are about the same if not more lenient than many other countries. Some have legal limit of 0.0.
I always get landblasted when I say that this is a feminine thing, but historically women are more against alcohol than men are. Examples are the prohibition phase in the 20s and MADD.
Re:On SUV safety (Score:2, Insightful)
Actually, SUV's might be expensive at the dealership, but they are very cheap to produce, hence the extreme profitability.
Re:weight& speed are the big issue here (Score:5, Insightful)
The suspension design, its geometry, and MOST IMPORTANT, the tires determine grip. (for normal road cars. For all-out race cars, aero is another way to generate grip.. but aero grip goes away when you slow down.)
If you put 20 dollar Wal Mart tires on your car, you deserve to die horribly in a no-grip accident.
If you treasure your life, and that of those you love, then fer $DEITY's sake, put decent rubber on your car. And that' doesn't mean "all seasons". It means summer tires for when it's not snowing, and snow tires for when it is.
Mass is the enemy. Less mass makes for better driving cars. Better grip, better control, better handling. More mass, the American Way, just ruins everything. That's just one reason why EVERYONE builds better-driving cars than America does.
Of course, if you have a small weenie, then your psyche demands you get a big honking chunk of ill-handling, ill-stopping, ill-steering Detroit Heavy Metal. To compensate, y'know.
Re:Physics of car crashes aren't intuitive. (Score:3, Insightful)
What I propose is that all vehicles that are not commercially owned (that is a separate issue) be grouped together. No distinction between the fuel consumption and crash standards for cars versus pickups & SUV's. Rate them all on the same scale, provide the same penalties to anyone who violates the accepted standards. If we applied the same standards to pickups that we do to cars, most would cost a couple thousand dollars more from the gas guzzler tax. And that is how it should be, no special priviliges to anyone.
low quality vehicals (Score:3, Insightful)
Minivans were the same way until too many people were killed and the rules tightened. If you take a close look at modern minivans they are essentially reinventing the station wagon.
Instead of exploiting loops holes, non-US manufacturers developed hybrids and high efficiency vehicals. SO now while US car companies are in trouble, foreign car companies are gathering up more market share. Just another sign that US business leadership is screwed. No vision, no intelligence, no ability or concern that we have known that world oil productuion would peak about 2005 (we have known this for about 30+ years). Just business as usual, play golf, out source and go for the short term.
Re:Builders wagon (Score:3, Insightful)
I like the idea, but sadly, it won't work here. Where I live, the jackasses in the giant suvs with "W" stickers just take as many parking spaces as they need. That is, when they're not driving around yelling unintelligible epithets at bicyclists.
Re:On SUV safety (Score:3, Insightful)
That's bullshit. My family went camping and boating dozens of times and has never owned an SUV. The SUV wasn't mainstream until the 90s.. you think people didn't camp and go boating before then?
Re:Well, that settles it then... (Score:2, Insightful)
However, I have seen countless news reports ("SUV crashes into schoolchildren") that imply that the vehicle caused the accident/collision/etc. of its own volition. On the other hand, when it is a subcompact or sedan, the report generally correctly places the culpability on the the responsible driver.
If I understood your message correctly, you believe that the very existence of SUV's/light trucks on the same road as any other vehicle is a safety hazard on the same scale as the removal of seatbelts and the installation of "impaling spikes". On the other hand, my opinion is that an unsafe driver is a safety hazard to self and others regardless of the vehicle driven. (Although certainly more damage can be done with a vehicle of greater mass.)
Repeat after me: (Score:3, Insightful)
Short version: you were lucky.
Sean
Re:Well, that settles it then... (Score:3, Insightful)
The "problem" is not cars moving to unibody - the improved safety and fuel economy drove that - the problem is millions of drivers using "light" trucks as their day-to-day vehicles, with no requirement that these trucks be designed with passenger car collisions in mind.
The good old days weren't as good as you say - body-on-frame collisions (such as the one I experienced in my dad's '74 Buick Centurion) were horrible compared to unibody-to-unibody collisions (such as the collision my wife experienced last month in her Hyundai Elantra.)
Re:weight& speed are the big issue here (Score:3, Insightful)
Unfortuneately... (Score:4, Insightful)
You can choose to optimize for avoiding accidents, or you can choose to optimize for an irrational hope that the ones you do have will be survivable.
By selecting an SUV, you've done the latter.
However, by doing so, you've chosen to have more accidents, more often. SUV's, irrespective of any other factors, have less grip than lighter vehicles merely because of their excessive weight, and because the load/grip ratio on modern tires is non-linear.. there's a fall off as load increases.
Additionally, the excessive girth of most SUVs means that you're fighting significantly more inertia than other vehicles. The horrible twist and non-rigidity in the construction means that any evasive maneuvers are uselessly slow - the body of the truck twists instead of directing the tires to move.
Everything the vehicle does is slow.. numb... subdued.
The high roll center means that more weight is transferred in all accelerative movements.. when turning you move more weight to the outside edge.. when braking you unload the rear tires more.. prior to high-roll-center SUVs being commonplace, rollovers were pretty much unheard of on paved roads. (when you leave the road, that's a different story).
even if you are the most situationally aware driver, when you pilot an SUV, you are motivating a stick of butter across a pan. You're driving a numb, useless instrument instead of a precision machine with proper dynamics.
You will be in more accidents, because you're driving a vehicle more likely to roll, more likely to twist/bend under dynamic conditions, that takes longer to stop, turn, and change direction, and which has lower road-adhesion characteristics for a given tire design than a lighter car would.
Also, your increased mass will tend to cause more damage to others around you.
All of this.. because you think you are better off if someone hits _you_? You've chosen a vehicle that makes it more likely you'll get hit (because it cant evade effectively.. and it's an enormous target). Your vehicle is more likely to roll in a side impact. Your vehicle has a very weak chassis, so unless the collision hits in just the right spot, the amount of body deflection and passenger intrusion will be more severe than in a well made unibody car.
I live in the midwest, so i understand the utility and necessity of large, ladder-frame vehicles perfectly well. But i dont own one, because i am not a farmer, construction foreman, or other blue-collar contractor. Trucks and SUVs have a purpose, but passenger safety for daily driving isn't it.
Congratulations, you've been deluded.
Re:Very biased (Score:2, Insightful)
You're right. A place calling itself the "Parners for Child Passenger Safety" is going to be very biased, but biased towards keeping children safe.
Is there any reason to think that they would be biased either for or against SUVs? I can't think of any reason. If you see one, please explain.
Perhaps you own an SUV and don't like the implications?
Hey, Sean, rollovers *can* be avoided... (Score:1, Insightful)
Collisions sometimes can *not* be avoided.
Thanks, I'll stick w/ my Dodge truck.
Thanks for your concern, though.
Re:weight& speed are the big issue here (Score:3, Insightful)
Re:weight& speed are the big issue here (Score:3, Insightful)
The problem is peak loads as the occupant collides with the interior of the car. The design goal is to keep the passenger in his seat, and the passenger compartment largely intact. A stiffer vehicle hitting a less stiff one causes the softer vehicle to absorb more than its share of the collision force, often exceeding the design force of the softer vehicle (that was designed to absorb only its own velocity, like when hitting the solid barrier in common crash tests).
Crash compatibility appears to be the greatest factor in crash surviability, and the hardest to measure. For example, the standard side impact test crashes a simulated front end of a Ford Tuarus into the car under test. Most vehicles do well in this test becuase the short soft Taurus tends to engage the door framing, pushing the test car away and spreading the impact force out. Try this same test with a taller stiffer vehicle impact and the passengers in the test vehicle are often killed. A famous test found that when the test vehicle was hit with a Dodge 4x4 pickup the passengers sustained much less injuries than when hit by the same model 4x2 pickup despite the 4x4's 800lbs of additional weight. It took many weeks of film analysis to figure out why... the 4x4 came with factory tow hooks mounted under the bumper. These hooks caught the top of the door frame and pushed the test car out of the way... the 4x2 version's bumper rode over the door frame and struck the dummy directly.
Mark
Re:Physics of car crashes aren't intuitive. (Score:3, Insightful)
So if we follow that logic should motorcyclists pay the least insurance, since from a damage to life and property motorcyclists face the greatest danager in any collison. Or you could flip it around and since motorcycles are lighter and in collisons they (or the riders) tend to become dangerous flying objects, perhaps we charge them more?
Also I won't argue that body on frame vehicles cause more damage to other vehicle(s), but you have to base libility premiums on whose at fault more often, and I have to think, based on the rates, that body on frame vehicles are at fault less often. Of the five vehicles I insure, two are body on frame, I pay more in libility for the unibody vehicles than the body on frame, which tells me that some statistics must show that unibody vehicles are at fault more often.