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Based upon a review of the literature and new test data, the human and vehicle factors leading to head-to-roof contact in rollovers are quantified and illustrated. Vehicle design countermeasures and suggested areas of research are presented. Higher and stronger roofs and improved restraints must be analyzed as a system to evaluate the potential benefits in rollovers.

Various factors were evaluated to determine their influence on the odds of front seat occupants receiving either fatal or serious/fatal injuries in single-vehicle rollovers. Factors evaluated included roof strength-to-vehicle weight ratio (as measured in accordance with FMVSS 216), and SAE H61 Effective Headroom. Roof strength-to-weight ratio had no statistically significant effect (p>0.05) on the likelihood of fatality or serious/fatal injury for belted or unbelted drivers. SAE H61 Effective Headroom had no statistically significant effect (p>0.05) on the likelihood of fatal or serious/fatal injury for seat belted drivers in rollovers.

Rollover crash and accident studies identify significant roof-to-ground impacts adjacent to the vehicle occupant as a potential cause of severe injuries. It is not possible with existing dynamic rollover test methods to specifically repeat or recreate a particular roof-to-ground impact in a controlled fashion. Variations associated with tire-to-dolly, tire/wheel-to-ground, and vehicle-to-ground interactions early in current rollover test methods tend to produce unpredictable and unrepeatable roof-to-ground impacts later in the test. A new test device now enables researchers to bypass the uncertainty of these first ground interactions by beginning each test with the desired roof-to-ground impact conditions as a test input. The new rollover test method releases a rotating vehicle onto the ground from the back of a moving semi-trailer.

In rollovers, belted occupants sustain a lower fatality rate compared to unbelted occupants primarily due to lower risk of partial or full ejection. However, seat belt and occupant compartment designs found in most current vehicles do not prevent head contact with the vehicle interior during a rollover because of occupant torso and head excursion that result from the rollover dynamics. An experimental study was conducted to simulate the airborne phase of a rollover. The goals of this study were to: 1) quantify the effect of restraint anchor locations and belt component designs in reducing head excursion, and 2) to better correlate the response between humans and an Anthropomorphic Test Device (ATD) during the high angular roll rate of the airborne phase of a rollover. A Head Excursion Test Device was designed to rotate a restrained occupant about an axis to approximate the inertial loading experienced during the airborne phase of a rollover.

Laboratory testing measured the response of a 1984 Chevrolet S-10 Blazer seatbelt buckle to impact on the back of the buckle. The peak acceleration, pulse duration and webbing tension were recorded to map the unique circumstances necessary to inertially unlatch the buckle. The conditions necessary to inertially unlatch the buckle in the laboratory were compared with the measured buckle responses in fifteen sled tests and six rollover crash tests using anthropomorphic dummies. All of the crash tested buckles remained latched and all had dynamic responses well below those required to produce inertial unlatching. Dummy hip areas were measured to be significantly stiffer than humans. Buckle accelerations measured in the “parlor trick” of intentionally striking the hip with a buckle are not representative of crash conditions.

Eight lateral dolly rollover tests were conducted on 1983 Chevrolet Malibusata nominal speed of 51.5 km/h (32 mi/h). Four of the vehicles had rollcages, and four had standard production roofs. Unrestrained outboard front GM Hybrid ill dummies with head and neck transducers were used. Numerous cameras documented the vehicle and dummy movements. Detailed vehicle kinematics data allowed quantitative analysis of the conditions for head and neck loads. For both roof structures, the dummies moved upward and outward from their seats due to rotation and acceleration of the vehicle. High head/neck loads were measured when the head contacted a part of the car experiencing a large change in velocity, often that part of the car which struck the ground. The results of this work indicate that roof strength is not an important factor in the mechanics of head/neck injuries in rollover collisions for unrestrained occupants.

Determining whether restraint systems were used in an accident is an important task of the field accident investigator. Restraint systems protect people by causing the forces which must be applied to the person in a collision of a particular value of to be applied to stronger parts of the anatomy over a longer period of time, and by helping to prevent ejection. Restraint use may cause characteristic changes in the vehicle at the mounting points, in the retractor mechanism, the restraint system hardware, and the webbing. Occupant Injuries will reflect altered occupant kinematics and altered load application areas when restraints are used.