ANN ARBOR—If you think that not wearing a seat belt affects only yourself, think again, say researchers at the University of Michigan Transportation Research Institute.

Federal regulations require automakers to meet safety standards that protect drivers and passengers who are not wearing their seat belts.

But removing these test requirements “might encourage the deployment of seat belt interlocks and allow optimization of restraints to focus on belted occupants,” says Jingwen Hu, associate research scientist at UMTRI and the College of Engineering.

Hu and colleagues compared the performance of restraint systems optimized for belted-only drivers and front-seat passengers with those optimized for both belted and unbelted occupants using computer simulations and field crash data analyses.

They found that unbelted requirements do not affect optimal seat belt and air bag designs for drivers and front-seat passengers in a mid-size sedan model and for drivers in a SUV model—only the restraints for SUV front-seat passengers are affected.

However, in their field performance evaluation, the UMTRI researchers removed energy-absorbing components of the knee bolsters (the lower padded portion of the instrument panel of a passenger vehicle) from the belted-only optimal designs.

“Removing the energy-absorbing materials in the knee bolsters would not affect the protection for belted occupants (represented by the crash dummy models) in the selected vehicles under the regulated crash conditions,” Hu said. “However, I think there is an more important systematic effect from both the knee bolster and the air bag together in some vehicles in real-world crashes.”

Compared to the optimal designs with the unbelted requirements, optimal designs without unbelted requirements generated the same or lower total injury risks for belted occupants, but they also increased the total injury risks for unbelted occupants.

As a result, if the seat belt use-rate increases from the current 86 percent to 95-99 percent, the total number of injuries could potentially decrease 0-10 percent by removing the unbelted requirements, Hu said.

“What is very clear is that removing the unbelted requirement will reduce the design constraints for optimizing the safety system. Consequently, it will likely improve the protection for belted occupants, even if automakers devote the same time and resources for belted occupant protection as before.”

More information:

• Study: Occupant Restraint Systems
• Jingwen Hu