Edward A. Moffatt

ROLLOVER CRASH TESTS - THE INFLUENCE OF ROOF STRENGTH ON INJURY MECHANICS

There has been ongoing research and discussion regarding the effect of roof strength on rollover protection since the 1950s. This chapter on the influence of roof strength on injury mechanics is from a comprehensive text on occupant and vehicle responses in rollovers. In this chapter, the authors report on a series of eight lateral dolly rollover tests that were conducted on 1983 Chevrolet Malibus at a speed of 32 mi/h (51.5 km/h). Four of the vehicles had rollcages; four had standard production roofs. Numerous cameras documented the vehicle and Hybrid III dummy movements during the tests. Results showed that, 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 that struck the ground). The authors conclude that roof strength is not an important factor in head/neck injuries in rollover accidents for unstrained occupants. In addition, there was no significant difference in the occupant kinematics between standard and rollcaged vehicles. However, the vehicles with rollcages had less glass breakage. The chapter includes extensive appendices that reproduce photographs from each of the 8 tests.

Matched-Pair Rollover Impacts of Rollcaged and Production Roof Cars Using the Controlled Rollover Impact System (CRIS)

The authors of this chapter, from a comprehensive text on occupant and vehicle responses in rollovers, report on a study of three rollcaged and three production roof vehicles were exposed to matched-pair rollover impacts using the Controlled Rollover Impact System (CRIS). The CRIS consists of a towed semi-trailer, which suspends and drops a rotating vehicle from a support frame on the rear of the trailer. The authors found that the roof-to-ground contacts were representative of severe impacts in previous rollover testing and real world rollovers. Results showed that the seat-belted dummies measured nearly identical head impacts and neck loads, with or without the rollcage, despite significant roof crush in the production roof vehicles. The peak head accelerations and neck loads were a result of the roof striking the ground and stopping and were not related to roof/pillar deformation. If humans were subjected to these same impact conditions, the rollcaged vehicles would not have protected them. The authors conclude that the CRIS is a very reliable tool to conduct repeatable rollover impacts with controlled dummy positioning.

Repeatable Dynamic Rollover Test Procedure with Controlled Roof Impact

Rollover crash and accident tests identify significant roof-to-ground impacts adjacent to the vehicle occupant as a potential cause of severe injuries. These tests also often provide information on dummy kinematics, as well as vehicle translational velocity, roll rate, and point of impact with the ground. However, there has not been a method to replicate these impact conditions through controlled dynamic rollover testing. In this chapter, from a comprehensive text on occupant and vehicle responses in rollovers, the authors report on a new test device that is repeatable. The tests enables researchers to begin each test with the desired root-to-ground impact conditions as a test input. The test method releases a rotating vehicle onto the ground from the back of a moving semi-trailer. The roll, pitch, and yaw angles, translational and vertical velocities, and roll velocity of the vehicle for the first roof-to-ground interaction is repeatable from test to test. The motion of the vehicle after the first impact is not repeatable, however. In addition to the standard onboard and off-board vehicle documentation, camera coverage from the rear of the semi-trailer is also now available.

Head Excursion of Seat Belted Cadaver, Volunteers and Hybrid III ATD in a Dynamic/Static Rollover Fixture

In rollover accidents, seatbelted occupants sustain a lower fatality rate compared to unbelted occupants, primarily due to lower risk of ejection. However, seat belts do not typically prevent head contact with the vehicle interior during a rollover, due to occupant torso and head excursion. This chapter on head excursion of occupants is from a comprehensive text on occupant and vehicle responses in rollovers. In this chapter, the authors report on a total of 80 excursion tests: 51 tests with a Hybrid III 50th percentile male anthropomorphic test devices (ATD); 18 tests with a cadaver; and 11 tests with two male volunteers. Results indicate that vertical head excursion was minimized with a steep lap belt angle and short webbing length, in tests using a two-point lap belt. Tests using a three-point lap and torso restraint showed that the torso belt reduced vertical head excursion primarily by restricting forward torso rotation. The authors also note that the ATD had less vertical excursion than either the volunteers or the cadavers; while the ATD is a useful tool in testing the effectiveness of restraint systems, it may not fully simulate vertical and lateral head excursion of humans in rollover conditions.

Factors Influencing the Likelihood of Fatality and Serious/Fatal Injury in Single-Vehicle Rollover Crashes

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.

Headroom, Roof Crush, and Belted Excursion in Rollovers

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.