New design could improve highway guardrail safety
The guardrails along America's highways haven't changed much since the 1960s, when the familiar W-shaped steel beam began reassuringly bordering the dangerous twists and turns.
Yet that reassurance has taken a hit recently, with evidence that traditional guardrail designs fail to protect some vehicle classes such as sport utility vehicles and four-wheel-drive trucks.
A University of Wisconsin-Madison engineer has developed a potentially safer replacement made from composite materials. The unique design made from glass fiber-reinforced polymers is meant to better "capture" the wide range of vehicles on the market, from hulking 4-by-4s to the tiniest compact cars.
After years of perfecting the design through computer simulation, civil engineer Lawrence C. Bank has just run his prototype gray beams through a battery of stress tests in the laboratory. So far, Bank says they exhibit their intended qualities of better strength and flexibility.
The beams are scheduled this spring for full-scale automobile crash tests, a key step for Federal Highway Administration (FHWA) endorsement.
"This is a perfect application for this type of material," says Bank. "Our emphasis has been on a lighter, more durable and rust-proof alternative to steel."
Bank and co-inventor Russell Gentry have a patent pending on the beam's unique geometry, which helps solve one of the major problems with current guardrails. Unlike the narrow depression of W beams, Bank's guardrails have a much wider "capture area" where the bumper impacts in an automobile crash. The capture area essentially helps control the vehicle, keeping it from climbing over or being forced under the guardrail.
That's a limitation with traditional guardrails. In October 1998, the FHWA banned any further installations of two of the most common metal guardrails, when crash tests showed they caused pickup trucks to flip over on impact. Safety experts now advise drivers of pickups and SUVs to use caution on bridges and sharp curves.
Bank says the problem is that while vehicles on the road have changed in the past 30 years, guardrails are from a time when car frames were more universal. Bumpers of trucks and SUVs run higher than the "capture area" of the rails, making them more likely to climb up and over the beams.
"We're hoping our design might be at the right place at the right time," Bank says.
"The crux of our patent is in how we make the composite fail in a very progressive fashion," he says. "These beams are designed to be pushed back three feet and still have their tensile capacity and connectivity."
The beams, made up of a series of rectangular cavities, break one layer at a time rather than all at once. Bank says the design absorbs more energy before failing, which can lessen the severity of impact.
Since the material is lighter, Banks says the beams can be produced in 25-foot sections that are twice as long as typical steel beams. Bolts for traditional beams would be replaced by a connecting rod and pin system, making installation faster and cheaper.
Cost may be an issue, Banks adds, because fiberglass composites run about $8 per foot compared to $4 per foot for steel. But add installation costs and Bank says traditional guardrails approach $15 - $20 per foot. With the savings in installation costs, Bank estimates that his design will be competitive.
Drivers probably give guardrails little thought, unless they're negotiating a hairpin curve or passing a steep drop-off. But about 15,000 Americans die each year after their vehicles careen off the road, the FWHA reports, making roadside rails a crucial part of highway safety.
The design work and creation of prototypes was supported by a Phase 1 grant from the Small Business Innovative Research program, a Department of Commerce initiative to promote university technology transfer. Small business partners include the Pennsylvania firms Creative Pultrusions and Technology Development Associates.