Report No. DOT HS 810 739

Charles J. Kahane, Ph.D. and Marcia J. Tarbet

November 2006

ABSTRACT

Federal Motor Vehicle Safety Standard (FMVSS) 201 – Occupant Protection in Interior Impact – was upgraded in 1995, with a 1998-2002 phase-in, to reduce occupants’ risk of head injury from contact during crashes with a vehicle’s upper interior, including its pillars, roof headers and side rails, and the upper roof.  Initially, energy-absorbing materials alone were used to meet the standard; later, some vehicles were also equipped with head-protection air bags.  NHTSA does not yet have enough crash data to evaluate the injury-reducing effectiveness of the energy-absorbing materials.  However, the agency has conducted 154 matched pairs of impact tests with free-motion headforms in pre- and post-standard vehicles of 15 selected make-models.  The Head Injury Criterion, HIC(d) averaged 909.9 in the 154 pre-standard tests and 667.5 in the post-standard vehicles.  This is a statistically significant average improvement of 242.4 units of HIC.

EXECUTIVE SUMMARY

The purpose of Federal Motor Vehicle Safety Standard (FMVSS) 201 – Occupant Protection in Interior Impact – is to reduce occupants’ risk of head injury in crashes.  The performance test requirements of FMVSS 201 limit the force allowed when a dummy headform impacts locations in the vehicle’s interior that might actually be contacted by occupants’ heads during crashes.  NHTSA’s major upgrade of FMVSS 201 in 1995 added the A-, B- and other pillars; roof headers; roof side rails; and the upper roof to the list of test locations.  The new requirements phased in during 1998-2002.  Initially, energy-absorbing materials alone were used to meet the standard; later, some vehicles were also equipped with head-protection air bags. 

The injury-reducing effectiveness of the energy-absorbing materials will ultimately be evaluated by statistical analyses of crash data.  As of November 2006, NHTSA does not yet have nearly enough crash data.  In the interim, this study documents the energy-absorbing materials actually installed in production vehicles and evaluates their effect on performance in laboratory tests.  The materials – located beneath the potential impact locations – include composite plastic foam padding, injection-molded ribs or ridges in parallel or egg-crate-like configurations, crushable tubes and more flexible designs for interior surfaces and components.

NHTSA purposively selected 15 high-sales make-models of passenger cars, pickup trucks, SUVs and minivans that had been tested for compliance with FMVSS 201.  A contractor purchased 15 pre-standard vehicles of the same make-models, and performed identical headform impact tests, at the same locations, as in the compliance tests.  (When an exact match was impossible because a make-model was discontinued or its interior redesigned, the closest corresponding model or location was selected.)  In all, there were 154 matched pairs of impact tests in pre- and post-standard vehicles.

The Head Injury Criterion, HIC(d) measured on the dummy headforms has been validated as a criterion for predicting head injury risk in crashes.  For compliance with FMVSS 201, HIC(d) must be 1000 or less at each tested location.

·        HIC(d) averaged 909.9 in the 154 individual pre-standard impact tests and 667.5 in the post-standard tests.  This is a statistically significant average improvement of 242.4 units of HIC(d).

·        HIC(d) exceeded 1000 in 47 of the 154 locations tested in pre-standard vehicles, but was less than 1000 in each of the 154 locations in the post-standard vehicles.

·        Only 2 of the 15 pre-standard vehicles, but all of the post-standard vehicles had HIC(d) ≤ 1000 at each location.

The analyses demonstrate a substantial improvement of HIC(d) after the FMVSS 201 upgrade for 15 high-sales make-models.  They provide the most positive evidence available, for the time being, that the energy-absorbing materials introduced in response to FMVSS 201 are likely reducing head injuries in crashes.