“We estimate that as many as 13 million people with osteoporosis, brittle-bone disorder, and hemophilia need some additional protection from forces applied to the torso during a car crash,” says Gary Sorock, an associate professor at the Johns Hopkins Center for Injury Research and Policy.

The students designed a vest filled with three layers of foam padding, each with a different density, to absorb some of the energy that causes a person's chest to compress during a crash. This energy can otherwise lead to broken ribs and other internal injuries. Replacing a conventional three-point shoulder belt with a four-point race-car harness helps distribute crash forces across a wider area of the body as well as keep the body held more tightly against the seat.

Testing at the Johns Hopkins Biomechanics Test Facility simulated a 108-lb woman. The dummy was belted onto a sled moving at 18.5 mph and carried sensors to gauge the effect of crashes on various parts of the body. Simulations were of a 20-mph head-on crash or a 35 to 40-mph crash involving a moving car hitting a parked vehicle. A high-speed camera captured close-up images of the dummy as it was jarred by the impact.

When the dummy was outfitted with the vest under conventional restraint, chest compression dropped by nearly 8%. With the vest and harness, sternal compression was cut by 17% to 2.9 mm. Crash impact forces, measured from the seat belt, dropped from 664 lb of force with a standard shoulder belt to 436 lb with the harness.