The objective of the present study is to evaluate a development of the conventional seat belt, offering improved control of anti-submarining and chest loads especially for smaller occupants.

The seat belt continues to be the prime safety system fitted to automobiles. Crash injury data indicates that performance improvements continue to be required, particularly in the rear seat and with smaller occupants in the areas of anti-submarining, adaptation to smaller occupants (such as children making the transition from using child restraints) and chest loads. World interest in simple low cost, lightweight vehicles for use in developing countries is emphasising this need.

The new belt system, the Lifebelt, retains similar belt geometry to current seat belt systems but with an extension of the seat belt webbing in a continuous loop around the upper thighs. It makes use of many available belt system components, and has the potential to allow a simple lightweight seat belt system with acceptable performance, without some of the complex add on systems now being used.

The evaluation began with static fit trials and then used dynamic sled testing under frontal crash test conditions similar to regulatory crash tests (50 km/h and 30g pulse). A number of sled tests (n=20) were carried out in front and rear seat configurations and with different seat structures reflecting current production as well as simplified seating. The new system was compared to conventional belt systems in typical seats and belt geometries. HIII 50M and HIII 5F dummies were used to assess the effect of occupant size, with the small female having the greater tendency to submarine. Anti-submarining effectiveness was assessed from video and with belt motion monitored by iliac spine force transducers, as used for Japan NCAP testing.

The enhanced system retains similar belt geometry and occupant use to current belt systems, with some changes to the seat structure for installation. The new belt with the extra continuous lap loop was shown to give a high level of anti-submarining performance while at the same time retaining good occupant kinetics and keeping the chest loads within acceptable limits. The system is able to reduce the need for add on components (such as the in seat anti-submarining ramp and pretensioners), which are required to give current, conventional seat belts acceptable performance.