From Traffic Safety Magazine:

                SUVs and Cars: Size Matters

by Sherri Deatherage Green

     Take a look around at any stop light, camp ground or soccer field parking lot and you will discover one basic truth about the automobile industry: Size matters.

       Bigger isn’t always better, at least when it comes to computer chips and stereo speakers.  But try to tell that to someone trying to squeeze three kids, two baseball bats, a cooler and a baby stroller into a two-door subcompact.  Those with stuff to haul and hills to climb will mutter a collective, “Yeah, right.”  Light-duty trucks made up 47.6 percent of all vehicles sold in 1998.  Sport utility vehicles, a subset of that broader category, represented 18 percent of sales, according to the Alliance of Automobile Manufacturers.

      Size matters for another reason, too.  Call it vehicular Darwinism.  When something big collides with something little, the smaller object usually loses.  Too often these days, it seems the smaller object is a car and the larger object is an SUV or pickup.

      Hampton C. Gabler, Ph.D., and William T. Hollowell have been studying this phenomenon for years and are quick to point out that despite the bad rap SUVs have been getting, they don’t deserve all the blame. Their research focuses on light trucks and vans, or LTVs, a category that also includes pickups, vans and SUVs.  Studies consistently show that while LTVs make up about a third of all registered vehicles, collisions between them and cars account for more than half of all fatalities in crashes involving two light vehicles.

     “The whole essence of this issue can be summed up if you look at the national fatality records in crashes between light trucks and cars,” said Gabler, an engineering professor at Rowan University in Glassboro , N.J.   “Eighty percent of the fatalities in those crashes occur in the car.”

The problem evolves

     The term “sports utility vehicle” may be relatively new to the American lexicon, but the autos they describe and the incompatibility problems they engender have been around for decades.  Chevrolet christened the Suburban brand name in the 1930s, noted Terry Rhadigan, GMC’s safety communications manager.  Suburbans usually stayed out on the farm with their pickup cousins.  Station wagons and large sedans accommodated the needs of most urban families.

     Then the Arab oil embargo brought us gas lines and high fuel prices.  Congress enacted the Corporate Average Fuel Economy Act, or CAFE, in 1975, which required cars to meet certain fuel usage standards.  Today, cars in each automaker’s fleet must average 27.5 miles per gallon and LTVs must average 20.7 mpg.

     In the decade following CAFE’s enactment, cars slimmed down and became much more fuel efficient.  The average curb weight for cars dropped 1,000 pounds between 1975 and 1985.  Lightness and safety, however, don’t always go hand-in-hand. In a study for the National Highway Traffic Safety Administration, Charles J. Kahane, Ph.D., estimated that decreased size and weight of cars contributed to almost 2,000 fatalities annually.  “Large vehicles have historically been more stable and provided more protection for their occupants than small ones, although those benefits to society might be offset if they present a greater hazard to other road users,” Kahane wrote.

     The number and size of passenger cars in the United States remained relatively static between 1985 and 1993.  Meanwhile, LTVs gained an average of 340 pounds and their numbers increased by 50 percent.

     Some CAFE critics claim the act drove consumers out of ever-shrinking sedans and into LTVs.  Relatively inexpensive gas, perceived safety, economic prosperity, and yes, even the occasional need to drive off-road undoubtedly boosted popularity as well.

    Young, affluent buyers led the SUV craze, according to a 1995 study by R.L. Polk & Co.  Most SUV owners earned more than $50,000 per year, led active lifestyles and fell into the 25-to-49 age bracket.  However, a proliferation of both luxury SUVs and small, economical models may since have widened appeal, said Nissan spokesman Dan Passe.

     The Gabler/Hollowell studies show that as far back as 1980, before the SUV love affair blossomed, more people were killed in cars hit by LTVs than vice versa.  By 1992, the number of deaths in car-to-LTV collisions exceeded those in car-to-car crashes, and the gap has been widening ever since.

Recipe for incompatibility

     Engineers and researchers generally consider two criteria when determining how different types of vehicles will interact in crashes, according to a 1999 study co-authored by Gabler.  Crashworthiness measures how well an automobile protects its own occupants, while aggressivity looks at the number and severity of injuries caused to people in other vehicles.  Because of their weight, SUVs generally do a good job of protecting those inside but not those outside.

      In a wreck involving a  Ford Motor Co. Excursion and a Yugo, it’s easy to guess which driver would be injured.  Weight might be the most obvious mismatch, but it’s not the only one.  The Excursion’s height and frame stiffness also decrease the other driver’s chances of walking away unharmed.

      The typical subcompact passenger rides a mere 175 mm off the road, while someone in a full-sized SUV sits nearly 400 mm high, according to a 1996 Gabler/Hollowell study.  Therefore, larger vehicles can override door sills of smaller vehicles, and the bumpers of larger vehicles can hit smaller vehicles at head level.

      LTVs also don’t absorb blows like cars.  Most models employ stiff frame-rail designs as opposed to unibody structures used in most cars.   “That stiffness is not going to serve you well because it won’t manage crash energy well,” explained Julie Rochman, spokeswoman for the Insurance Institute for Highway Safety.   In a wreck with an LTV, a car takes on a disproportionate amount of the crash energy, causing it to sustain more damage.  Stiff design also can cause frame or mechanical components to ram through to the SUV’s passenger compartment.

      Side-impact collisions are especially dangerous to drivers of cars hit by LTVs.  Research by Gabler and Hollowell shows that when SUVs hit cars in side impacts, 30 car drivers are killed for every one fatally injured SUV driver.  When such crashes happen head-on, 5.6 car drivers die for each SUV driver killed.

      While the inequities between LTVs and passenger cars may be more apparent, Gabler pointed out that wide variation in size and body styles among vans, pickups and SUVs creates imbalance even within that market segment.  “Super SUVs can be incompatible with other light trucks,” Gabler said.

Kinder, gentler LTVs

      Crash tests and compatibility research projects are ongoing at NHTSA.  “It’s not working toward a regulation but to identify things that indeed can be done,” said Hollowell, who is chief of NHTSA’s crashworthiness research division.  “Cooperation [with automakers] has been relatively good over the last year.”

      “In the engineering world of today, no vehicle is an island,” said AAM spokeswoman Gloria Bergquist.  “Our roads have gotten incredibly diverse.”  Bergquist’s organization, financed by automakers, is undertaking its own crash tests and research on international vehicle compatibility and side-impact injury patterns.

      Individual automakers are working on ways to make their LTVs less damaging to smaller cars.  General Motors built its 2000 model Suburbans and GMC Yukon XLs about two inches lower and 200 lbs. lighter than the 1999s, for example.  Mercedes designed a front crumple zone for its ML 55 AMG to absorb more crash energy. It also uses a frame design that won’t override passenger car bodies.

       When Ford rolled out its mammoth Excursion last year, it also introduced its BlockerBeam technology.  The BlockerBeam is a T-shaped device attached underneath the SUV’s frame to better match its impact height with other vehicles, explained spokeswoman Sara Tatchio.  The system worked so well Ford plans to install it on its F-250 and F-350 pickups.  Ford’s new smaller SUV, the Escape, features a reinforced fender and a second load path that routes some crash energy through the roof, Tatchio said.   “It keeps some of the energy from going into the other vehicle” in a collision, she added.

       Improving compatibility is a two-way street.  Passenger cars must be built safer, too, experts agree.  Most automakers are developing or installing side air bags on at least some models to better protect occupants.  Air bags that protect both the head and the thorax are most effective in LTV/car collisions, noted Bob Yakushi, manager of Nissan North America’s engineering analysis department.

       SUV fever shows no sign of cooling among American consumers.  But people who buy them because they feel safer in larger vehicles may be fooling themselves.

      While sheer weight gives SUV drivers an advantage in vehicle-to-vehicle wrecks, about 40 percent of all fatalities occur in single-vehicle accidents.  So highway deaths involving cars and trees may be more common than those between cars and SUVs.  Rollover propensity has driven up collision insurance rates for SUVs, said Loretta Worters, spokeswoman for the Insurance Information Institute. Liability insurance rates haven’t increased, although Worters said she wouldn’t be surprised if they had.

      “Statistically speaking, when you compare utility vehicles to cars of similar weight, you are better off in a car,” Rochman said.  “People shouldn’t get a false sense of security because they are riding up high.  That height does come with some consequences.”


Roll Over

     Remember that old jingle about the toys that wobble but don’t fall down?  Those little figures were so bottom-heavy you could thump, kick or throw them and they always landed right-side up, unlike SUVs.

      SUVs generally are top heavy, so when they wobble, they can tend to roll over.  Passenger cars, on the other hand, sit lower to the ground and don’t roll as often.

       According to a NHTSA report, 37 percent of fatal rollover accidents in 1996 involved SUVs.  Pickups, at 25 percent,  and vans, at 19 percent,  fared somewhat better, but only 15 percent of fatal rollovers involved cars.  Considering that the entire light truck and van, or LTV, category, made up only a third of registered autos at the time, the statistical imbalance is all the more striking.

     Occupants not wearing seat belts often are ejected through windows in rollovers, increasing the likelihood of serious injury or death.  Ford is combating that problem with a new type of air bag introduced at this year’s Detroit auto show, said Gloria Bergquist of the Alliance of Automobile Manufacturers.  The air bag drops down like a sheet between the driver and the window and stays inflated for six seconds, long enough for a vehicle to flip several times, Bergquist said.  Other automakers are working on stability control systems that would make SUVs easier to maneuver when drivers swerve, she added.

     NHTSA has initiated a rulemaking process aimed at creating a scientific standard for measuring rollover propensity, said spokeswoman Elizabeth Neblett.  One idea being tossed around is the so-called static stability ranking, a formula expressing a ratio of vehicle height to track width.  Wider vehicles tend to be more stable than those with narrower wheel bases.

     Automakers argue that a static stability ranking wouldn’t take vehicle movement and other variables into account.  “The biggest contributor is driver behavior,” added Ford Motor Co. spokeswoman Sara Tatchio, whose employer supports education programs for SUV drivers.  Some people feel bolder and drive more aggressively behind the wheel of a large vehicle, she said.  “If you are in an SUV or a light truck, you need to drive less aggressively.”

      A certain demographic segment of SUV owners may have bought sports cars in years past. These drivers should understand that a Chevy Blazer, for example, never will take corners like a Camaro.  “You shouldn’t drive it like you would a car,” said Julie Rochman of the Insurance Institute for Highway Safety.  On a sharp curve, gravel, ice or snow, a low-slung car might slide or skid, she noted.  “A utility vehicle is going to roll over.”

1998 LTV Facts

·         The 2.8 million SUVs sold represent 18 percent of total automobile market.

·         The 7.4 million total LTVs sold (including SUVs, pickups and vans) accounted for 47.6 percent of the automobile market.

·         Two-wheel-drive SUVs tallied the highest number of deaths per registered vehicle in single-auto crashes (127 per million).  In multiple-vehicle collisions, car fatalities (80 per million) ranked higher than pickups and SUVs.

·         Half of the traffic fatalities in SUVs occurred in single-vehicle accidents, compared to 35 percent in pickups and 19 percent in cars.

  Sources: National Highway Traffic Safety Administration and Alliance of Automobile Manufacturers.

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