The government and the Institute evaluate the strength of vehicle roofs by pushing a metal plate into the roof of a stationary vehicle. Because crash test dummies aren't used, the static test can't directly provide key information about injury risk to occupants involved in real-world rollover crashes. Nor can this static test evaluate the effectiveness of restraint systems like safety belts, rollover curtain airbags, and padding in vehicle interiors.
A dynamic test could fill in the missing data. However, the best way to conduct such a test and how to evaluate the results are still under debate.
Real rollover crashes occur in lots of ways, and engineers have come up with different kinds of tests to address various aspects of these crashes — dolly rollovers, curb trips, dirt trips, corkscrews, and fallovers, among others. No single test best represents the broad spectrum of actual crashes.
Measuring how a roof crushes in a dynamic test is trickier than in a static test, and some testing methods would preclude having dummies inside the vehicles. The dummy itself is a problem because none of the existing types was designed to assess injury risk in a rollover crash. Some dummies may not even move like people do when turned upside down.
A further complication is that many rollovers are preceded by other events that may affect occupants' positions when their vehicles roll. This means researchers will have to figure out the best position for a dummy in a dynamic test.
In the end, specifying a dynamic test is a big task that's only just started. In the meantime, Institute research shows that making roofs stronger as measured in a relatively simple test will prevent many injuries and deaths in rollover crashes.