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Disclosing Rollover Propensities to Improve Auto Safety

In 2000, a series of widely-reported traffic fatalities associated with rollovers of popular sport utility vehicles (SUVs) drew national attention.These incidents, which also involved sudden tread separation in certain lines of Firestone tires, highlighted a more general public safety problem. SUVs were more likely than sedans or station wagons to roll over, and some SUVs were much more likely to roll over than others.


Improving public understanding of the propensity of vehicles to roll over was important because rollover accidents remained the most deadly auto accidents in the United States and were increasing. Rollovers accounted for less than 4 percent of all auto accidents but accounted for about a third of driver and passenger fatalities (61 percent of SUV fatalities and 22 percent of passenger-car fatalities). From 1991 to 2001 the number of drivers and passengers killed in all automobile accidents in the United States increased by 4 percent, while deaths in rollover accidents increased by 10 percent. Light-truck (including SUV) rollover fatalities increased 43 percent, whereas passenger-car rollover fatalities declined 15 percent.


Improving public understanding of rollover risks was also important because federal rules did not set any minimum safety standards for new-model rollover performance, as they did for front and side impact crashworthiness. The auto industry had successfully opposed such a standard for two decades.


In response to the Firestone/SUV accidents, Congress approved a new targeted transparency system aimed at informing car buyers’ choices and providing incentives for manufacturers to design vehicles less prone to rollovers. The Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act of 2000 required public disclosure of the rollover propensity of each new-model car and SUV as measured by government tests.


Regulators required rollover ratings to be presented in a simple five-star format that paralleled the existing star rating systems for front and side impact crashworthiness. A five-star vehicle had a 10 percent or less chance of rolling over while a one-star vehicle had a 40 percent or more chance of rolling over.


The new law and regulations added other disclosure requirements. They required tire pressure monitoring sensors by 2004, automakers’ disclosure of information on customer complaints and other early indications of safety defects, and new labels to make it easier for car owners to see if their tires had been recalled.


Disclosure improved over time. The TREAD Act included an innovative provision that required that the government’s initial mathematical modeling of rollover propensity be replaced with a road test that would more accurately mimic real-world driving conditions. Congress also directed the National Academy of Sciences to study possible tests quickly and required regulators to consider the academy’s recommendations. As a result, officials instituted a more accurate test in 2004 that combined modeling with driving maneuvers to complement the initial static test. In 2005, Congress further increased consumer access to rollover information by requiring that rollover ratings be posted on new-car stickers in auto showrooms.


Early evidence suggested that auto rollover disclosure helped to inform consumers and encourage safer new-model design. Five years after the requirement was introduced, only one model (the Ford Explorer Sport Trac) received as few as two stars, while twenty-four models earned four-star ratings. Congress’s Government Accountability Office concluded that ratings were “successful in encouraging manufacturers to make safer vehicles and providing information to consumers.” Manufacturers used ratings as a marketing tool in television and print ads.


Interestingly, this targeted transparency system also helped to change the politics of auto safety regulation. By encouraging manufacturers to accelerate introduction of new stabilizing technology, the rollover rating system reduced industry opposition to a minimum safety standard for rollovers. In 2005, Congress directed regulators to issue such a standard.


However, as of 2006, the rollover rating system still had significant weaknesses. The system relied on government rather than manufacturer tests. As a result of budget and logistical constraints, not all new-model cars were tested, and some test results were not available until late in the model year. Ratings also did not allow consumers to compare the safety of specific models across weight classes. In addition, backup data for star ratings remained difficult to access. Consumers had to delve into the government’s docket management system or research and development Web page, or visit the National Crash Analysis Center near Washington, D.C.


Rollover star ratings themselves remained controversial, as did the longer-established star ratings for crashworthiness in front and side impacts. The Transportation Research Board, as well as consumer groups and auto insurance associations, charged that star ratings gave consumers a falsely positive impression of safety, since one-star vehicles could have a 40 percent chance of rolling over, and that ratings diminished in usefulness when most vehicles earned four or five stars.


This case study is drawn from Full Disclosure, Fung, Graham and Weil, 2007.


National Highway Traffic Safety Administration

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