Interest in rear-seat occupant safety has increased in recent years. Information relevant to rear-seat occupant interior space and kinematics are needed to evaluate injury risks in real-world accidents. This study was conducted to first assess the effect of size and restraint conditions, including belt misuse, on second-row occupant kinematics and to then document key clearance measurements for an Anthropomorphic Test Device (ATD) seated in the second row in modern vehicles from model years 2015-2020.
Twenty-two tests were performed with non-instrumented ATDs; three with a 5th percentile female Hybrid III, 10 tests with a 10-year-old Hybrid III, and 9 tests with a 6-year-old Hybrid III. Test conditions included two sled bucks (mid-size car and sport utility vehicle (SUV)), two test speeds (56 and 64 km/h), and various restraint configurations (properly restrained and improperly restrained configurations).
Head and knee trajectories were assessed. Head excursion was 38 percent greater with the 5th percentile female ATD than with the 6-year-old ATD when lap-shoulder belted in the 56 km/h sled tests with the passenger car. Contact between the head and the seat was only observed when the shoulder belt was placed behind the torso with the 5th percentile female and with the 10-year-old ATD, irrespective of vehicle type.
In the static seated position, the nose-to-seatback was more than 11 cm greater with the SUV than with the passenger car used in the sled test series. The analysis of clearance data indicated that the relative distance between the nose and the seatback was smaller in modern compact SUVs than modern small cars at 53.5±5.3 cm and 57.6±5.9 cm respectively. Knee clearance was also lowest in compact SUVs than other vehicle types.
The sled test results in combination with the clearance measurements, highlight an increased potential for head contact between the second-row occupant and front seatback in small cars and compact SUVs in frontal crashes, in particular when an occupant is improperly restrained.