Background Rollover crashes are one of the most significant safety problems for all classes of light vehicles, especially light trucks. According to the 2001 FARS, there were 10,647 vehicles involved in fatal rollover crashes. FARS shows that 20 percent of light vehicles in fatal crashes involved rollover. The proportion differs greatly by vehicle type: 16 percent of passenger car vehicles were involved in rollover, compared to 25 percent for pickup trucks, 19 percent for vans, and 35 percent for sport utility vehicles (SUVs). The 2001 General Estimates System (GES) estimates that 296,000 light vehicles were involved in a rollover crash. Eighty-two percent of rollover crashes are single-vehicle crashes. The TREAD Act of 2000 specified that the agency develop and promulgate consumer information on the rollover performance of light trucks and SUVs. This measure of rollover resistance, the Static Stability Factor (SSF) was added to the MY 2001 NCAP tests and is reported in Buying a Safer Car on a scale of 1 to 5 stars. The SSF is a measure that equals one half of the track width divided by the height of the center of gravity above the road. This measurement identified the location of the center of gravity of the vehicle and correlated this to the risk of a tripped rollover crash. Linear and logistic regressions were run in 2000, using MY 1994 to 1998 vehicles, to determine and verify the relationship between SSF and rollover rate. It was found that the correlation of SSF to rollovers per single vehicle crash is remarkably robust in an area as complex as rollover.

Objectives Track the trend of the SSF to determine if current models have a higher SSF (and are therefore less prone to rollover). Determine whether there has been a trend to lower rollover rates in the most recent models. Compare SSF and rollover rates for earlier and later vehicles when there has been a major model redesign.

Proposed Approach Use State crash data to determine rollover rates of current as well as earlier model year vehicles. Obtain track width and height of center of gravity data on earlier model year vehicles for which NHTSA has current SSF measures, particularly those that have undergone a major design change. This evaluation can probably be completed within a year, since it is based on analyses of existing data; it should be updated from time to time.