Consumer safety ratings organisations have published static ratings of the head restraint geometry, with the aim of raising public awareness of correct head restraint positioning, and encouraging vehicle manufacturers to improve geometry. The geometry of front seat head restraints has improved each year, but the rear seats have not been investigated. Research into protection against whiplash injuries has shown that reducing the head restraint backset and improving height is effective in reducing real world injury risk. In comparison to the front seats whiplash injuries occur less frequently in the rear seats, but rear seat occupancy can be as high as 12%. The research objective in this paper is therefore to examine the head restraint geometry of the rear seats in comparison to the front seats, by presenting a feasibility study for geometric rating of the rear seats and an initial set of ratings for over 100 car models.
The RCAR-IIWPG procedure for static geometric rating of head restraints was adapted for use in the rear seats, allowing for the associated space and practical considerations. An H-Point Machine (HPM) with Head Restraint Measuring Device (HRMD) fitted was used to measure the horizontal backset from the head to the head restraint, and the height from the top of the head to the top of the head restraint. The measurements were rated according to zones of Good, Acceptable, Marginal, and Poor.
115 rear seats were rated from a variety of mainstream cars, with the top sellers selected for each vehicle manufacturer. Both the outboard and centre seats were rated where applicable. Only 9% of outboard rear seats rated as Good, but 2% of centre seats. 42% of the outboard seats rated as Poor, but for centre seats this was increased to 69%.
In comparison to the front seats the rear seat ratings were much poorer. The front seats have 91% rated Good, and 0% rated Poor. However nearly half the rear seats are rated Poor, and only 9% are rated Good. Whiplash prevention technologies have focussed on the front seats, but consideration must now be given to the rear seats.
The paper offers a new insight into the protection offered by rear seat head restraints against whiplash injuries. The ratings can be used by consumer safety organisations to increase public awareness and to encourage development of rear seats that can offer protection against whiplash injuries.