In Search of the
Perfect Seat Belt
Research continues on this effective safety device.
Yet for many NASCAR drivers, race fans and even everyday motorists, the idea that a seat belt—especially a heavy-duty one designed for racers—might split or rip apart was unthinkable to begin with.
Indeed, the device that safety advocates universally hail as the single most important safety item in today's vehicles is notable both for its amazing durability and straightforward, mostly low-tech design.
And even as seat belts continue to save an estimated 11,000 Americans from death in car crashes annually, automotive researchers continue to look for ways to improve the belts. If the safety experts have their way, U.S. drivers may go from today's three-point safety belts to four-point belts—similar to those found in race cars—and back-seat riders may wear seat belts that inflate.
Belts Date Back Decades
The first patent for an automotive lap belt was granted in 1907, but it wasn't until 1956 that a major U.S. carmaker offered the device. That year, Ford Motor Co. included front and rear lap belts in its optional Lifeguard Safety Package.
Developed by Ford for automotive applications, the belts were two inches wide and constructed of very tightly woven nylon. Nylon was the material of choice because it was affordable, very strong and reasonably flexible. Two-inch-wide belts offered the optimal protection—by way of distributing crash energy across the body's vital parts—in most car crashes, which occur at 30 miles per hour or less.
This isn't to say wider belts wouldn't provide more protection in some situations. "You're constantly battling comfort versus performance," said Dr. Stephen Rouhana, staff technical specialist and group leader in Ford's safety research and development department.
While a wider belt better distributes crash forces in general, "I think there are issues with people wearing it," Rouhana said, noting that wider belts are stiffer and less comfortable. For example, a three-inch wide belt inherently can't conform across a person's lap as snugly as does a two-inch-wide belt, he said.
Europeans Joined In
Swedish carmaker Volvo upped the ante in 1959, when it introduced in Europe the first automotive three-point safety belt, patented a year earlier. But it, too, was a two-inch-wide belt of nylon construction when it made its way to the States as standard equipment on all Volvos in 1963.
Anticipating an imminent federal mandate, U.S. carmakers began installing lap belts on cars in the mid-1960s. The U.S. National Highway Traffic Safety Administration made them mandatory Jan. 1, 1968, and by 1972 some form of a combination lap/shoulder belt for each front, outboard seating positions was required. Beginning with the 1974 model year, NHTSA allowed only a fully integrated, continuous-loop-type, three-point belt.
Around the same time, in the early '70s, carmakers began replacing nylon with polyester as the belt fabric of choice. No, it wasn't trendy leisure suit polyester—it was a stronger, heavy-duty industrial version, more along the lines of the tie-downs used on flat-bed 18-wheelers. Woven into a two-inch wide belt, it equaled or bettered the strength of nylon but in a lighter, more flexible and more comfortable construction.
Riders Crash Into Interiors
Seat belts were the first attempt by carmakers to address what auto researchers in the 1960s called the "second collision" that occurs during crashes.
The first collision is a car hitting something—another car, a tree, a road sign. The second collision involves riders in the car hitting parts of the car's interior. Simply, a car's occupants are traveling at the same speed as the car when it hits an obstacle, and the harsh reality is that absent some form of restraint, occupants will crash into the dashboard, steering wheel, seatbacks, window pillars etc., at that same speed.
According to NHTSA, three-point belts are very effective in reducing the chance of death or serious injury from a second collision. Government officials estimate the belts reduce fatalities by 45 percent and serious injury by 50 percent.
NHTSA also has calculated how well seat belts prevent ejection from a vehicle during a crash. Getting tossed out of a vehicle is, NHTSA said, "one of the most injurious events that can happen to a person in a crash." Indeed, three of every four occupants ejected in a crash in 1999, the last year figures were available, died. But only one out of 100 motor vehicle occupants wearing seat belts were ejected during a crash.
Looking at Better Belts
Early in 2001, Ford went public with two new belt systems that are under study. Each would adapt for use in consumer vehicles a four-point belt system initially developed for motor racing.
One is a suspender-like system comprising two shoulder belts dropping down vertically over each shoulder and connecting to a center-buckled lap belt. The other is a "cross-your-heart" system comprising two of the traditional shoulder belts criss-crossing the chest.
Volvo is researching similar systems, but includes adjustable seats to ensure the belts are properly positioned for all sizes of occupants.
Each of these systems more firmly restrains a person's torso than does the current, three-point belt system in today's cars. Each also is integrated into the seat, as opposed to being attached directly to a car's structure via the B-pillar.
Integrated Belts Can Be Costly
While there are positives to both systems, each also raises potentially troubling issues.
The first seat offered in the U.S. that incorporated a three-point belt—on the 1990 Mercedes-Benz SL—"was a very expensive seat," said Fred Heiler, spokesman for Mercedes-Benz USA, Inc. It was an aluminum/magnesium casting "that was very aircraft/technology-like." It also required re-engineering of the seat tracks and unibody to which the seat was bolted to ensure the structure could handle the added stress.
In the years since, however, Mercedes-Benz has devised a more-conventional, welded-up steel seat assembly that's less costly. And properly designed, a seat belt integrated into a seat can be more comfortable, and therefore more likely to be used, he added.
Bob Lange, executive director of safety integration for General Motors Corp., which offers belt-integrated seats on some of its cars and light trucks such as the 2001 Chevrolet TrailBlazer, 2001 Oldsmobile Bravada and 2001 GMC Envoy concurred that such seats cost more to build but, interestingly, don't boost safety ratings. "We were hoping to record a [safety] performance improvement, but it didn't happen," Lange said. "We found we could provide the same level of protection with a body-mounted belt."
Restricted Movement an Issue
Heiler also reported reservations Mercedes-Benz researchers had about the more restrictive four-point belt systems. "They really hold the upper body in too rigid a position," he said. And that could contribute to the kind of whiplash-induced skull fracture that is believed to have ultimately caused Earnhardt's death.
Volvo and Ford officials said their designs and anticipated applications of four-point belts either avoid or minimize the chance of such a skull fracture. Much like today's three-point belts on inertia reels, the seat belt systems Ford is evaluating "allow movement of the body," Rouhana said.
Their most promising benefit, he said, is that they "may be able to retain the occupant better in a crash on the other side of the car," where today's standard, outboard, single shoulder belt provides minimal restraint.
Volvo is a bit more reserved. "We're only investigating [the four-point belt] as a front-seat opportunity," said Roger Ormisher, vice president for public relations at Volvo Cars of North America, Inc. By that he means one intended first to better restrain an occupant in a low-speed collision and second to properly position an occupant for the deployment of an airbag. "It's not really a harness that's pulled tight," he cautioned.
A Seat Belt That Inflates?
Carmakers also are looking at a hybrid belt that combines the best of a seat belt and an airbag.
Ford demonstrated its "inflatable safety belt" at the 2001 North American International Automobile Show in Detroit in January. The system comprises a shoulder belt containing an airbag that instantaneously inflates when a car is involved in a collision.
Ford officials said the system spreads the forces of a crash over a broader section of the body than a traditional, two-inch-wide seat belt does, thereby minimizing the "whipping" forces imposed on the upper torso and neck.
While variations of the four-point belt are in the early stages of evaluation, "I will say that we are very far along in the engineering of the [inflatable belt] system," Rouhana said. "In actuality, we've been eyeing inflatable belts as a rear-seat application, because it's very problematic to package an airbag for a rear-seat person. You have to package it in the back of the seat in front of you, which is the seatback of the front seat occupant, and there are issues with that."
And officials at Honda Motor Co. started looking at what they call "air belts" about five years ago. A spokesman, however, declined further comment.
New Belt Materials Possible
Other researchers are looking beyond varying a seat belt's configuration. They're studying that polyester material.
Honeywell International Inc., for example, has developed what it calls a "smart fiber" that stretches in a controlled manner in a car crash. This eases the stress on the occupant in much the same way as the elaborate assembly of mechanical, electronic and even pyrotechnic pretensioners and force limiters carmakers are currently using.
The new fabric, which Honeywell has dubbed "Securus," would allow the elimination of such devices, saving not only costs but providing a better seat belt.
"Today's seat belts are actually too strong," said Craig Trask, Honeywell's business manager for Securus, and can, in fact, contribute to fatal injuries "like in the Earnhardt crash."
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