Initial rollover effectiveness evaluation of an alternative seat belt design for agricultural tractors

A test program was conducted to determine the effectiveness of a seat belt restraint in preventing occupant movement in a rollover accident. A baseline type-2 seat belt (pelvic and torso restraint), and an improved type-2 seat belt restraint, both designed to restrict occupant motion in a rollover accident, were tested in a rollover restraints tester (RRT). Each seat belt was placed on a H-III 50th percentile male dummy and testing conducted at a single roll rate and two D-ring adjustment positions. Each test simulated what was approximately a 260 degrees per second rollover parallel to the longitudinal axis of the tractor with the top of the ROPS impacting the ground after 180 degrees of roll. Forces on the dummy's head and neck were measured, and video was taken to measure the head motion in the x-, y-, and z-axis of the dummy. The average vertical, forward, and lateral head movement in the baseline seat belt was 144, 222, and 184 mm, respectively, when the adjustable D-ring anchorage supporting the shoulder belt was in its lowest position. At the lowest D-ring height, the shoulder belt became ineffective and the seat belt performance became similar to a type-1 restraint (required for tractors with ROPS) resulting in increased vertical, forward, and lateral movement. The improved restraint reduced vertical head movement by as much as 75% without increasing head and neck loads above established injury criteria. Testing seat belts for rollover effectiveness will become increasingly important as seat belt usage on tractors with ROPS increases.