Options Exist for Stronger Roofs
Structural foam, high-strength steel would absorb impact, create 'simple fix,' some say.
Here are some ways automakers could bolster vehicle roof strength:
* High-strength steel. Alloys can add strength without weight, but tend to be costlier.
* Structural foam. Cheap and well-known, keeps beams from bending.
* Automaker options
* Reinforced pillars. Makes them stronger during a crash.
* Roll bars. Can be blended into a roof structure, keeping them invisible to passengers.
Sources: Center for Auto Safety, Union of Concerned Scientists, Monash University
WASHINGTON â€” Building stronger vehicle roofs is relatively simple by auto industry standards, and the technology to do it has been available for decades, engineers say.
â€œStrengthening roof pillars to sustain a rollover is a trivial structural engineering exercise,â€ said Raphael Grzebieta, president of the Australasian College of Road Safety, an organization of automotive researchers based in Australia.
Some examples are already on the road today.
Ford Motor Co.-owned Volvo of Sweden, for example, employs a high-strength, boron-steel alloy to reinforce the roof structure of its Volvo XC90 SUV. The alloy is light and strong, but more expensive than conventional steel.
But there are also inexpensive options.
Engineers say the U.S. auto industry could greater utilize technologies such as structural foam, used extensively in the production of aircraft, and high-strength steel. Foam is cheap and easy to work with. The material stiffens and ensures that hollow steel beams donâ€™t bend or lose their structural integrity. It also absorbs energy during a crash.
â€œAutomakers have cheap technology at their fingertips to do it,â€ said Grzebieta, an engineer with Monash University in Australia. â€œThe amount of material that would need to be added to the roof pillars is really a small percentage of the vehicleâ€™s overall costs. Rollover is really a simple fix.â€
In addition to high-strength steel and structural foam, engineers say, automakers have several other options, such as:
* Roll bars integrated into a vehicleâ€™s roof structure. In a report released last year called â€œBuilding a Better SUV,â€ the Union of Concerned Scientists and the Center for Auto Safety estimated a roll cage could be incorporated into a passenger car roof structure for about $50 and would add 15 pounds of weight.
* Stronger roof pillars. one way to strengthen the roof structure is to add steel tubes inside the A pillar, which frames the windshield. Automakers also can change the shape of roof pillars to add strength.
* Better roof design. The XC90 has rounded corners on its roof. That means it is less likely to hit the ground hard during a rollover. A vehicle with square corners, like the Hummer, is likely to catch the ground harder and absorb a greater impact.
â€œIf you tell an automotive engineer to make a roof 10 times stronger, he will be able to do it,â€ said Carl Nash, a former NHTSA official now working on roof-crush lawsuits. â€œBut you just need something strong enough to keep its basic strength in a rollover. To do that, you need something more like 1 1/2 or two times the (current) strength.â€
Other kinds of safety technology might emerge once the NHTSA develops a more sophisticated regime of testing â€” one that would measure how crash test dummies are injured in simulated rollovers.
That sort of crash test is known as a dynamic test. NHTSA does dynamic crash tests for other common types of crashes, like frontal and side-impact crashes.
Agency officials say that is a long-term project when it comes to rollovers. NHTSA administrator Dr. Jeffrey Runge told lawmakers on Capitol Hill that the agency did not know of any dynamic tests that could meet a basic legal requirement â€” repeatability.
But researchers are working on them. At least three devices have been developed that claim to be dynamic and repeatable:
* Fordâ€™s Controlled Rollover Impact System. The CRIS device consists of a truck trailer equipped with a scaffolding that holds a car or truck. The scaffolding is able to rotate the test vehicle at a predetermined rate while the tractor-trailer moves forward. The suspended vehicle is then dropped on a test track.
* Don Friedman, a former GM engineer who now consults on safety issues for plaintiffsâ€™ attorneys, advocates a system by A. Jordan & Co., a California testing firm. It uses a giant rotisserie-like device to rotate a vehicle cab, while on the surface below, a steel structure is moved to impact the roof like the ground would in a rollover crash.
* Australian researchers at Monash University, trying to address concerns about rollover deaths in the Australian army, proposed using a system that combined elements of a drop test and the CRIS truck. A vehicle is suspended from a crane on the back of a truck traveling at 30 mph.
While the NHTSA hopes to update rule 216, Runge cautions that improving roof strength alone only will help in a fraction of rollover crashes.
Thatâ€™s why the agency is looking at new kinds of seat belts, technologies like side air bags and electronic stability control, along with a new roof-strength test.
â€œOne single countermeasure isnâ€™t going to solve this problem,â€ Runge said. â€œWe have to look at the vehicle as a system.â€