Jun 23, 2008

Car, Truck or SUV: Which Is Safer?

Carly Scissors wanted a new Jeep Wrangler because she thought it "looked cool." Her parents decided to buy it for her because they believed an SUV would give the 19-year-old student the best line of defense in a serious accident. "If you're going to have your daughter driving around, you want her in something safe," explains stepfather Elliott Milstein, president of a small Michigan pharmaceuticals company. "And we'd read all the reports in the papers saying you're more likely to survive an accident being in a truck."

The Milstein family is by no means unique. Millions of American motorists are trading in their sedans, coupes and station wagons for minivans, pickups and sport utility vehicles. While style, utility and versatility are among the advantages that light trucks offer, for many buyers, safety is the major selling point.

But are sport utility vehicles really as safe as they seem? That's become the centerpiece of a debate that's growing even faster than the SUV market itself. To critics, they're "killer trucks." Yet others cite the same data to make their case that sport utes are among the safest things on wheels. As is common when an issue becomes so polarized, the real answer is somewhere in between.

Down and Dirty Data

According to 2005 statistics collected by Insurance Institute for Highway Safety (IIHS), very large sport utility vehicles, like the Dodge Durnago and the Chevrolet Suburban, have the lowest death rates on the road—about 24 occupants killed for every million registered vehicles no more than three years old. At the other end of the spectrum are mini cars, such as the Mini Cooper or the Toyota Yaris. As a group, they average 144 deaths per million registered vehicles. Midsize SUVs, including the Honda Pilot or Nissan Pathfinder, average 57 deaths, while midsize cars, like the Ford Fusion and Honda Accord, run as high as 70 deaths per million vehicles. Average things out and you are, on the whole, safer in an SUV than you are in a passenger car—their death rate ratio is 47 per million compared to 86. (2005 is the most recent year available. Remember that statistics fluctuate over time, and these could change.)

The biggest problem with SUVs, however, is that in a crash, they have a higher risk of rolling over than cars. Not surprising, when you consider the potentially troublesome combination of a short wheelbase and a high center of gravity. In 2004, 62 percent of SUV occupants killed were involved in rollovers according IIHS. That rate drops to 23 percent in cars. Although there are a number of factors-like age and experience of the drivers-that influence these stats, the biggest advantage SUVs have is their size and weight.

But how does this effect other smaller, lighter cars on the roads?

Crash Facts: Call Me Incompatible

It takes only an elementary understanding of the laws of physics to recognize that "when big runs into little, big tends to win," as Ford Motor Co. safety specialist Ernie Grush says. It's a concept automotive experts have dubbed "compatibility."

Smash an 18-wheeler into a subcompact and there's no contest. Obviously, the odds also are stacked in favor of a Chevrolet Suburban slamming into the side of a Chevy Cavalier. "You are always at a disadvantage in a small, light vehicle, no matter what type of crash," said Russ Radar of the IIHS. On the whole, when an SUV and a passenger-car collide, the car occupants are about one and a half time more likely to suffer fatal injuries than if they collide with another car.

Side impacts are about the most deadly vehicle-to-vehicle collision. Accordingly, side-impact survivability has been the most recent focus of automotive safety engineers. Today's automobiles are designed with a lot of crush space that will fold up like an accordion—in a frontal or rear-end collision—helping absorb much of the crash energy. When you're hit in the side, however, there's simply not much room to "ride-down," or absorb the impact forces. So run a full-size passenger car into the side of a small one, and you're still 20 times more likely to die if you're sitting inside the car that's being hit.

Weight and Stiffness: A Geometry Lesson

Just how serious a problem is the car-truck imbalance on our roads? According to the most recent NHTSA Fatality Analysis Reporting System (FARS) numbers, 57 percent of fatal crashes involve only one vehicle. However, when there is a second vehicle involved and it's a matter of big vs. small, small vehicles just don't have the material to absorb the energy of a crash, therefore it's easier for their passengers to get hurt; while utes might be more likely to rollover, their greater mass provides passengers with greater protection in multi-vehicle accidents.

Of course, all safety experts--from the government, insurance companies and the automakers--agree that we could slash highway fatalities by getting everyone to buckle up.

That said, one can't dismiss the compatibility issue entirely. "Weight has a big effect," says Priya Prassad, one of Ford's top safety researchers, as do factors such as vehicle stiffness and geometry.

Geometry refers to the fact that light trucks tend to ride higher than cars and usually have longer front and rear overhangs (the amount of vehicle between axle and bumper). So when a large SUV, such as the Ford Excursion TK, T-bones a small car, it's not uncommon for the SUV's bumper and hood to penetrate into the car's passenger compartment-something that can result in fatal head injuries. And even in frontal accidents, high-riding trucks often "over-ride," or climb on top of, the car they're hitting.

As for stiffness, while cars combine body and chassis in a relatively yielding unibody package, most trucks mount their bodies on rigid steel frames. That's useful when you're designing a vehicle for rough off-roading or to haul a heavy trailer. But in an accident, a truck's stiff frame rails can knife into the vehicle it hits, something Adrian Hobbs, of Britain's government-funded Transportation Research Laboratories, calls the "fork effect."

The challenge, industry officials counter, is to address compatibility issues without trading off the utility and versatility that SUV and other light-truck owners value. It's also essential, stresses GM's safety expert Tom Lange, that "you don't do anything that will compromise the safety of light-truck occupants in order to improve the safety of someone in the car they might hit."

Crossovers: Is It a Car or a Truck?

In recent years, automakers have introduced a new type of vehicle that addresses rollover, compatibility and other issues, like fuel economy, that give SUVs a bad name. Enter the crossover SUV: a car-truck hybrid that despite their SUV-looking bodies, rides on passenger-car chassis, creating a lower center of gravity and better aligning it's front-end with other cars. Research from IIHS shows that the fatality risk is 20 to 40 percent lower for car occupants in crashes with SUVs with lower front-ends than traditional models.

These crossovers, which include the Buick Rendezvous, Chevrolet Equinox, Ford Edge or Honda CR-V, offer several advantages besides compatibility. First, there's a car-like ride with the cargo space of an SUV. And with rising fuel costs, the more important attribute to many drivers may be that they're often more fuel-efficient; since they're modeled partly after a car, they weigh less.

New Standards: Safety Sells

Other steps are being taken that would have a far greater reach in making the roads safer. More and more auto-manufactures are choosing to offer safer side airbags to improve protection of vehicle occupants in side-impact crashes-the most deadly type of crash. When a car is struck by a larger vechile, the passanger's heads are especially vulnerable, therefore airbags that protect the entire upper-body (head, chest and torso) have shown to reduce driver deaths in cars struck on the driver's side by an estimated 37 percent, according to the IIHS. About four out of every five new cars and SUVs offer side airbags that protect the head.

The newest proposed safety standard, FMVSS 126, which is expected to be enacted in the next few months, specifically addresses the rollover issue: It would require electronic stability control (ESC) on all passenger cars, trucks and multipurpose vehicles. An extension of antilock break systems, ESC senses how well a vehicle is responding to steering input to the driver. If the tires start to slip or if the vehicle moves is a direction other than where it's being steered, the system kicks in to help the driver regain control. ESC can break wheels individually or make other adjustments automatically, reducing the risk of rollovers in single-vehicle crashes involving cars by 70 percent while it lowers the same risk in SUVs by a whopping 80 percent.

It used to be said in the auto industry that "safety doesn't sell." Don't try to tell that to today's buyers. Safety has become one of the most important factors in the purchase decision, and while automakers once dragged their feet whenever a new government standard was enacted, the smarter manufacturers now move even faster than the government mandates. ESC is already standard on 40 percent of 2006 passenger vehicle models-all Audi, BWM, Infiniti, Mercedes and Porsche have it-and it is optional on another 40 percent. Most automakers plan to at least offer the system on all vehicles in the next few years. IIHS estimates that as many as 10,000 fatal crashed could be avoided each year if all vehicles had ESC.

In sum, because of more car-like designs and ESC, the sports utility vehicles of today are a much safer vehicle than those of five years ago. But all else being equal, bigger vehicles provide an added measure of protection in an accident. Says Adrian Lund, president of the IIHS, "The laws of physics work." So, if crashworthiness is your bottom line, SUVs do help put the odds in your favor.

via : popularmechanics

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