Among seat/head restraints the Institute evaluated in dynamic tests, more are rated poor overall (30) than good or acceptable (24). Proportions are better in Europe, where 45 of 88 seat/head restraints tested by Thatcham in the United Kingdom are good or acceptable, and 16 are poor. Another 26 weren't tested dynamically because of inadequate head restraint geometry.
Only 8 of the 73 seat/head restraints the Institute evaluated dynamically earned good ratings. In contrast, 18 European seats are rated good. Besides Volvos, some European Ford, Nissan, Renault, and Seat models earned good overall ratings.
Like the Institute, Thatcham is a member of the International Insurance Whiplash Prevention Group. This U.K. research group conducted the dynamic tests of seats sold in cars in the European market, while the Institute evaluated seats sold in cars in North America.
International protocol for rating seat/head restraints
Overall ratings are based on a two-step evaluation. First a head restraint's geometry (distance behind and below the top of the head of a seated average-size man) is rated good, acceptable, marginal, or poor. Seats with good or acceptable restraint geometry then are subjected to a dynamic test simulating the forces in a stationary vehicle that's rear-ended by another vehicle of the same weight going 20 mph.
In the dynamic test, measurements are recorded on a dummy (BioRID) representing an average-size man. Dynamic ratings are derived from two seat design parameters (peak acceleration of the dummy's torso and time from impact initiation to head restraint contact with the dummy's head) plus tension and shear forces recorded on BioRID's neck during the test.
The overall ratings of 73 seat/head restraints are based on both geometry and dynamic test results. Twenty-four other seats with marginal or poor head restraint geometry weren't tested dynamically because they cannot protect taller people in rear-end crashes. These seats are rated poor overall.