The expected improved performance of a combined restraint system where an airbag supplements the conventional safety belt was not reflected in reduced g-values on the dummy's chest. However, by the distribution of force over the wider area of the airbag and the corresponding reduction of the specific pressure exerted by the three point belt, improved occupant protection is actually produced. Therefore, measurable quantities other than acceleration should be selected to evaluate the risk of chest injury, such as belt load or chest deflection.
A new method to measure the deflection of dummy ribs with strain gauges has been developed. The resulting data indicate a significantly reduced chest deflection when a combined system is used.