Insurance Institute for Highway Safety tests roof strength of minicars

The Smart Fortwo has the strongest roof and the Chevrolet Aveo the weakest among the 2009 micro and minicars recently tested by the Insurance Institute for Highway Safety (IIHS).
The Smart earns the highest rating of good compared with acceptable for the Honda Fit, Hyundai Accent, Mini Cooper and Toyota Yaris. The Aveo is rated marginal, an IIHS release says.
Vehicles rated good must have roofs that are more than twice as strong as the current minimum US federal safety standard requires.
In the institute’s test, a metal plate is pushed against one side of a roof at a constant speed. To earn a good rating, a roof must withstand a force of four-times the vehicle’s weight before reaching five inches of crush, the IIHS explains.
This is called a strength-to-weight ratio. For an acceptable rating, the minimum required ratio is 3.25. A marginal rating value is 2.5. Anything lower than that is poor, it continues.
“Small cars should have an easier time with the roof strength test. Their light weight means their roofs don’t have to work as hard to keep the structure around the occupants intact in a rollover.” said Adrian Lund, IIHS’s president.
“Compared with the current federal standard of 1., a strength-to-weight ratio of four reflects an estimated 50% reduction in the risk of serious or fatal injury in single-vehicle rollover crashes,” he added.