Four Beats Three

Way back in 1959, Swedish carmaker Volvo introduced the world's first production three-point seat belts. In those days, use of simple lap belts was very low, so the innovation went largely unnoticed. But through the years, this one safety feature has saved an estimated 123,000 lives, quite impressive for a few pounds of nylon and steel.

Last year alone, approximately 11,000 people owed their lives to three-point belts, and that number would almost double if more people used seat belts.

Now the auto industry is poised on the brink of another innovation, closely related to the three-point belt. Volvo, its parent Ford Motor Company, and other auto manufacturers are investigating various types of four-point safety belts. These belts, which a similar to seat belts used in racecars, secure both shoulders rather than running diagonally across the torso. Because of this, four-point seat belts distribute the crash forces over more of the chest, reducing the pressure on the ribcage, heart and lungs. They also help hold the occupant in place during crashes that put limitations on today's belt designs.

Volvo and Ford are collaborating on four-point seat belt research with a team headed out of Sweden by Christer Gustafsson, Volvo senior safety engineer, and David Wagner, Ford safety technical specialist. Two innovative styles are being evaluated by the team: the "X4" design and the "V4" design. The "X4" belt system utilizes a standard three-point belt plus a single belt that comes over the shoulder, down across the torso and attaches near the lap belt buckle. The "V4" design owes even more to automobile racing. It uses two shoulder belts, so fitting it is like putting on a backpack. Each belt goes over a shoulder and secures in a buckle on the lap belt. Both designs have been shown to be effective in rollover and side impact crashes during laboratory tests.

One major unknown about four-point belts is how users will accept them. Just as with three-point belts, four-point belts do no good if they are left sitting on the seat cushion. To determine their acceptability, during the Detroit International Auto Show, Ford asked show attendees to assess ease of use and comfort for both styles.

"We were very eager to watch people's reactions and discuss their concerns," Wagner said. "Consumers were very excited about the prospects of additional safety benefits from the four-point belt. We're still weighing the advantages of both designs."

Both engineers feel they are close to coming up with production-ready four-point belts that are acceptable to both the public and governmental agencies.

"While a few engineering challenges remain, I believe we'll have something in the next three years that meets the expectations of our engineering teams here in Sweden and Dearborn and of course those of our customers," said Gustafsson. "In the near future, we will be entering into discussions with regulatory agencies around the world including the U.S. National Highway Traffic Safety Administration (NHTSA), to discuss our findings and the regulatory implications of four-point belts."

While it seems four-point belts are on the way, this is no time to ignore the advances in three-point belts that we have seen over the years. Today's three-point belt design is quite different from its distant 1959 parent. Thanks to advances in materials, research, testing and real world use, seat belts are more effective than ever. Safety engineers also have better tools to help understand how a human body acts and reacts to vehicle crash dynamics, which has resulted in incremental gains in seat belt design.

For example, today seat belt webbing can be manufactured to stretch at a controlled rate to help soften the human load following a frontal impact. Also, by the addition pyrotechnic pre-tensioning technology, slack in the belt can be reduced milliseconds after impact, thereby helping to position the occupant properly for an impending crash. With the seat belt designs of today, when used in combination with a frontal airbag, vehicle occupants have never been better protected. Of course, seat belts must be worn for the driver and passengers to get the benefit of this research and technology.


Just to play it safe, Tom Ripley, a frequent contributor to Driving Today, wore a seat belt while writing this story. He covers the world automotive scene from his home in Villeperce, France.