Department of Transportation Introduces New Roof Strength Standards; Windshield Breakage Impact Reviewed in Study
May 4, 2009

The U.S. Department of Transportation's National Traffic Highway Safety AdministratioN (NHTSA) has introduced new roof strength standards for vehicles. The new regulations double the current strength requirements for light vehicles (up to 6,000 pounds) and adds requirements for heavier vehicles.

The new regulation for light vehicles specifies that both the driver and passenger sides of the roof must be capable of withstanding a force equal to three times the weight of the vehicle. The current standard calls for roofs to withstand 1.5 times the weight of the vehicle, applied to one side of the roof, for light vehicles up to 6,000 pounds.

Heavier vehicles (from 6,000 to 10,000 pounds) must now have both sides of the roof capable of withstanding a force equal to 1.5 times the weight of the vehicle.

"Rollovers are the deadliest crashes on our highways and today's rule will help occupants survive these horrific events," says Transportation secretary Ray LaHood.

The new standards will be phased in, beginning in September 2012, and will be complete for all affected vehicles by the 2017 model year.

In its final report regarding the new standards, NHTSA includes a section on its study with regard to the windshield and the structural role it plays, and notes that some safety advocacy groups suggested it remove the windshield of the vehicle prior to roof strength testing.

"Advocates, Boyle, et al, CFIR, Consumers Union, DVExperts, IIHS, Public Citizens, Penn Engineering and Perrone commented that windshields often break in a rollover, and stated that the agency should not specify a test procedure with windshields in place," reads the report.

However, NHTSA reports the following findings in its report: "The agency believes that windshields provide some structural support to the roof, even after the windshield breaks, because the force-deflection plots in some of the recent test vehicles (e.g., Ford Explorer, Ford Mustang, Toyota Camry, Honda CRV) show little or no drop-off in foce level after the windshield integrity was compromised."

The group also writes that "further examination of real-world crashes indicates that the windshield rarely separates from the vehicle, and therefore, does provide some crush resistance. Because NHTSA believes that the vehicle should be tested with all structural components that would be present in a real-world rollover crash, we decline to propose testing without the windshield or other glazing."

NHTSA also reports that in its investigation of rollover crashes the majority of windshields were coded as either "in place or cracked" or "inplace and holed."

"Less than 10 percent of weighted incidents indicate the windshield is 'out of place,'" writes NHTSA.

CLICK HERE to read the full report.

Need more info and analysis about the issues?
CLICK HERE to subscribe to AGRR magazine.