Bigger bodies require changes in car design
THE BOSTON GLOBE
Automakers are struggling with how to deal with a growing segment of buyers: obese Americans.
Like airlines, hospitals, and clothing and furniture makers, auto companies are adjusting to an ever more obese American population. With little fanfare, car makers are incorporating engineering and designs that efficiently, comfortably, and safely take the obese into account.
That's one reason why the Honda Accord sold in the United States is 2 inches wider than the similar model that Honda sells in Europe and Japan.
It's one reason why seats in some General Motors models have longer rails to slide on, allowing more space between the driver and the steering wheel and the airbag inside it.
It's one reason why adjustable pedals, marketed as a way to move short drivers away from airbags, ensuring their safe operation, also allow drivers with large midsections to move well back from the steering wheel.
And it's one reason why a Japanese manufacturer is developing inflatable seat belts that could cushion the impact of bones swathed in a soft, fat body with a taut seat belt during a collision.
Much of the engineering and design changes are happening below the radar. An auto industry adage proclaims that "you can't sell an old man's car to an old man," and it is also accepted that a car billed as built for the obese would turn away many buyers.
So just as elderly drivers have found cars that suit their needs, obese buyers are beginning to learn to try out cars and find the unheralded features that suit them.
The minute a vehicle is branded as being for a group such as the obese, "you've limited your audience," said Sam Locricchio, manager of communications for group design at Chrysler Corp. "Those who aren't that, or who are but don't want to be called that, aren't going to buy it."
The number of obese car buyers is growing. The American Medical Association estimates that 31 percent of adult Americans are obese. As a result, the auto industry is quietly on alert, not just over issues of comfort presented by obesity, but also over safety.
"The fact that people are getting larger is something we all have to consider," said Debra A. Senytka, engineering specialist for occupant accommodation at GM.
Overweight people have an increased chance of injury or death in an accident. A 2002 study by the University of Washington at Seattle reported that a person weighing 242-262 pounds was more than twice as likely to die in a crash as a 132-pound person. Part of the reason is extra weight hurtling forward; part of it is that obese people tend to have more underlying health problems that make recovery from injuries more difficult; and part of it is that at times it can be harder to extricate an obese person from the tight grip of a crumpled wreck.
But the main problem is one of simple physics, said Richard Kent, assistant professor of mechanical and aerospace engineering and emergency medicine at the University of Virginia at Charlottesville.
In a crash, a seat belt is meant to tightly and instantly grip bone: hip, sternum, shoulder, ribs. That means that fat isn't a safety cushion in a crash. It can be harmful.
An obese person, with several inches of fat between belt and bones, is loosely belted because "body fat is like air, like a gap between you and the belt," Kent said. Potentially catastrophic contact results, because "the bigger you are, the more force over a longer period of time needs to be applied to stop you."
This means that, in a crash, the belt snaps back through that gap and slams into the skeleton or organs as they hurtle forward. If the seat belt does not quickly encounter the pelvis, for example, "it goes into your bowel, your stomach," Kent said. "You can only put a few hundred pounds of force on it before you start tearing things up."
Testing has shown that this gap might let the obese slide from behind seat belts during rollovers.
To better understand the needs of obese people, automakers have helped fund the Civilian American and European Surface Anthropometry Resource, a private-public project more commonly called CAESAR, directed by Kathleen Robinette, a research anthropologist at the Air Force Research Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio.
The CAESAR study has used a 3-D scanner to log images of 13,000 men and women, from anorexic to morbidly obese. These figures, shot standing and sitting, are used not only in car design, but also for military purposes, furniture manufacturing, and in the clothing industry.
Car makers are using the images to electronically place them behind the wheel or in the passenger seats of their vehicles.
Take one of these images, Robinette said, "put them in the seat, and you say, 'Oh, wow, that person's not going to be able to turn the steering wheel!' "
But for designers and manufacturers, said Kent, the balance between building for the obese and building for smaller drivers and occupants is precarious. What benefits one group might impose discomfort or danger on another.
"By the end of the day, you only have so many arrows to hit so many targets," he said.
