The National Highway Traffic Safety Administration (NHTSA) regulates automobile manufacturers to try to protect consumers. NHTSA also broadcasts information on recalls, safety problems, vehicle testing, and research. Featured on our website is some information about safety ratings for vehicles based on the NHTSA static stability factor formula.

The proposed rating system was based on equal intervals of risk and positioned the five-star level at a value of SSF achievable by favorably designed family sedans. It also positioned the one-star range where it captured some popular SUVs and pickup trucks of the recent past. The manufacturers of the one-star vehicles generally have improved the current versions of the equivalent vehicles to the two-star level, but we believe the one-star rating ceiling would be stringent enough to discourage companies from returning to old design practices or from importing less advanced vehicles.

A fortuitous feature of the ratings based on the linear regression curve was that reasonable one-star and five-star SSF boundaries occurred at predicted levels of rollover risk of 10 percent and 40 percent, permitting three equal intervals of risk between them divisible by ten for the two-star, three-star and four-star boundaries. Having the star rating intervals bounded at 10, 20, 30 and 40 percent rollover risk levels would make the meaning of the ratings easier to explain to consumers. Figure 2 presents the proposed rating system in graphical form. The updated linear regression curve in Figure 1 is nearly identical to the linear regression curve in Figure 2, except that it would set the one star boundary for 40 percent rollover risk at 1.03 instead of 1.04.

NHTSA has examined vehicle stability on and off for 30 years without promulgating a rule; however, the agency began a consumer information rollover resistance rating in 2001 ranking new cars and light trucks based on Static Stability Factor (SSF). In response to the Ford/Firestone debacle, Congress ordered NHTSA, through the TREAD Act passed in November 2000, to develop a dynamic test for rollover resistance. The Phase IV report summarizes the testing and rates various on-road rollover resistance tests and was the basis from which NHTSA announced it would begin testing vehicles using J-turn and fishhook maneuvers. Real-world injury and fatality data continue to show the significant dangers associated with rollovers, forcing the issue to become a regulatory priority. Data compiled from federal sources indicate rollovers are the second most dangerous crash type (second only to head-on collisions). Fatality data from 2000 show 9,882 occupants were killed in light vehicle rollovers, 8,146 of which were single vehicle crashes. Not surprising, light trucks stand out: 78 percent of single-vehicle crashes in SUVs involved rollover; 63 percent for pickups and 60 percent for vans and minivans. Passenger car occupant fatalities in single vehicle crashes involving rollovers accounted for 46 percent. Data from 1996-2000 estimate 61,000 occupants receive incapacitating or fatal injuries annually in rollover crashes. These data also indicate 212,000 single vehicle rollovers resulted in 50,000 incapacitating injuries or fatalities.