Umeå University Medical dissertation

Background: Neck injuries in rear-end collisions are still a major problem both for the injured and, in terms of cost, for society. The latest generation of rear-end whiplash protection systems, as found in the WHIPS Volvo and SAHR Saab, have reduced injury rates by almost 50% in comparison with the previous generation of seat/head restraint systems. Occupant behaviour, such as seated posture and seat adjustment settings, may affect the injury risk. Method: Five studies were conducted. Study I was an injury outcome study based on insurance data. Studies II-IV investigated seat adjustment, occupant backset, and cervical retraction for drivers and occupants in different postures and positions in the car, during stationary and driving conditions. Finally, study V compared the occupant data from studies II and III with a commonly-used vehicle testing tool, the BioRID dummy, using the protocols of the International Standardization Organisation (ISO), the Research Council for Automobile Repairs (RCAR), and the RCAR International Insurance Whiplash Prevention Group (RCARIIWPG). Results: Female drivers and passengers had a threefold increased risk for medicallyimpairing neck injury in rear-end impacts, compared with males. Driver position had a double risk compared with front passenger seat position. Female drivers adjusted the driver seat differently to male drivers; they sat higher and closer to the steering wheel and with more upright back rest. The volunteers also adjusted their car seat differently to the ISO, RCAR, and RCAR-IIWPG protocol settings; males sat 61 mm and females 20 mm further away from the steering wheel, and seat back angle was 1 ̊ more upright in males and 4 ̊ more upright in females than in the protocols. In stationary cars, backset was highest in the rear seat position and lowest in the front passenger seat position. Males had a larger backset than females. Resting the hands on the upper part of the steering wheel increased the backset by 26 mm in females and 37 mm in males, in comparison with having the hands in the lap. Cervical retraction decreased and backset increased for both sexes when posture changed from a selfselected posture to a slouched posture. Backset was 41 mm greater in females and 43 mm greater in males during driving, in comparison to stationary conditions. The BioRID II dummy was found to represent a 35–45 percentile male in stature, a 35 percentile male in weight, a 96 percentile female in stature, and a 69 percentile female in weight in the volunteer group. Conclusion: Risks in car rear-end impacts differ by sex and seated position. Seated posture affects backset size and cervical retraction capacity, and hence the risk for end-range loading of cervical joints. The current BioRID II dummy does not represent the female population very well; and the ISO, RCAR, and RCAR-IIWPG testing protocols do not take sex and seated position differences into account. This thesis indicates the need for a 50 percentile female BioRID dummy and re-evaluation of the ISO, RCAR, and RCAR-IIWPG protocols, and further developments of new safety systems to protect occupants in rear-end impacts.