After wrangling with the Bush administration, regulators under President Obama have announced dramatically strengthened roof-crush requirements for cars starting in 2012. 

Today, as many as 10,000 people are killed in rollover accidents every year. While rollovers account for less than 10 percent of car accidents, they account for almost one-third of the fatalities. 

In response to public comments on two earlier proposals, this ruling will increase the amount of weight car roofs must be able to support in a rollover, and it will expand the requirement to include larger passenger trucks. The new standard also sets a minimum headroom requirement that must be maintained in a rollover. This requirement seeks to decrease the chance of the roof hitting an occupant’s head.

Under the current standard, passenger cars are tested using an angled metal plate that is pressed down on the front corner of a car’s roof. Using a force of 1.5 times the vehicle’s unloaded weight, the plate cannot deform the roof more than five inches.

Under the new regulations, the strength requirement will be doubled to three times the vehicle’s weight. The test will also be performed on both sides of the car’s roof sequentially. This new test method more accurately mimics a rollover crash, where one side of the roof hits the ground first, breaking the windshield and weakening the structure, then the weakened roof hits the ground on the other side. The roof would still have to withstand a force of three times the vehicle’s weight in the second part of the new test.

The new requirement also includes a provision limiting how much the roof can intrude on occupants’ headroom in a rollover. Under the force applied in the test, the roof can neither move more than five inches (as under the old standard), nor place more than 50 pounds of force on the head of an average-height male occupant.

Larger passenger vehicles that weigh more than 6,000 lbs. fully loaded, such as Hummer H2s, will be subject to the new two-sided test, but at the old 1.5 times strength-to-weight ratio. Vehicles greater than 10,000 lbs are still excluded from the requirement.

In addition to the new federal regulations, the Insurance Institute for Highway Safety (IIHS) has recently published results of its own roof crush tests. IIHS’s tests are only done on one corner of the roof, but require an even higher strength-to-weight ratio of 4:1 to get the highest rating of Good.

The new regulations will be implemented in conjunction with a requirement that all cars be equipped with electronic stability control (ESC) for 2012. ESC, which helps prevent a vehicle from skidding or sliding in a turn, is expected to reduce the incidence of rollovers by as much as 59 percent in SUVs, and more than 34 percent in cars.

—Eric Evarts