Handling and comfort evaluation of extra seat belt concepts for rear seat passengers

Report, 2014

Pre-crash car manoeuvres may contribute to head injuries to restrained children in frontal impacts. Evasive steering manoeuvres can cause the shoulder belt to slide off the shoulder resulting in excessive forward head excursion. This can allow the head to get in contact with the seat back in front of them. The overall aim of this project was to evaluate different restraint concepts that can maintain the rear-seated occupant well restrained during evasive manoeuvres prior to frontal collisions. Two extra seat belt concepts, named CrissCross (CC) and BackPack (BP), for the rear seat of a passenger car were developed and installed in a Volvo V60. In the project aspects such as handling and comfort were studied, as well as user acceptance and attitude towards the two extra seat belt concepts. To fulfil the goals of the project three different studies were performed; the Guessability study, the Attitude study and the Comfort study. The studies were carried out with children, youths and adults as test subjects. The guessability study was a field study where 100 persons testing handling of the extra seat belt when seeing it for the first time. In the attitude study, 5 focus groups were conducted to explore the user’s attitude to and acceptance of extra seat belts. Moreover, in the comfort study 32 and 14 test subjects respectively evaluated use aspects such as comfort and user experience during one-hour and three-hour car rides respectively. Subjective data, colleted through interviews and questionnaires, were analysed. The data provided comprehensive information as well as understanding of how the user experienced the extra seat belts in a realistic usage situation and also their attitudes towards the extra seat belts and which factors that affect the acceptance of the product. Generally the test subjects showed a positive attitude towards the extra seat belts. Both children and adults appreciated the increased feeling of safety and after having tried both concepts in the comfort study 90 % (for CC) and 70 % (for BP) respectively said that they felt safer travelling with these belt concepts than without. Comfort was considered an important factor in both the attitude and the comfort study. Body shape and size affected the seat belt fit to a great extent and the fit of the extra seat belts affected the comfort experience for most test subjects, both initially and over time. Comfort together with the feeling of safety was pointed out as having greatest impact on preferred concept. In the attitude study 86 % of the participants preferred CC after having tried both concepts for a couple of minutes. After having tried the concepts for one hour each in the comfort study, 56% of the participants preferred CC. This result strongly indicates that the comfort experience of the extra seat belt changes over time. Those who liked CC best appreciated its symmetry, comfort and the feeling of safety. Some test subjects found CC unpleasant to wear because the belts tended to slip close to the neck, described as a strangling feeling. The test subjects who preferred BP thought it was simpler to handle and that it did not cause the same strangling feeling as CC did. Negative characteristics with BP were that it felt asymmetric to use and not as safe as CC. To conclude, this project provided a first evaluation on how people experience extra seat belts in the rear seat of a car, and which factors that affects attitudes towards it. The studies show that besides reliance in the safety of the product, comfort, information about benefits, launching approach and habit of using the product are important factors when it comes to gain acceptance. The project result contains much valuable knowledge that can benefit further development and introduction of new seat belt concepts in cars.