Unless they're nosing into one, most drivers don't think much about guardrails. But a claimed increase in the number of accidents in which guardrails have impaled cars has recently vaulted the roadside protectors into the news.

Fingers are pointed at Trinity Industries, a Dallas, Texas, company that supplies guardrails and other roadside safety installations. The company altered the design of a part it sells nationwide. But, according to one study, the new part is four times as likely as its predecessor to be involved in a fatal accident. Several states across the U.S. have banned further installation of Trinity's device.

The part in question is an end terminal. When you picture a guardrail, you prob­ably picture a W-beam. These wavy barriers are the most common type of guardrail, resembling a "W" turned sideways when viewed end-on. They're designed to deform and absorb collision energy without pushing the vehicle back onto the roadway. If struck on its end, a W-beam would slice into a car like a spear. The end terminal is supposed to prevent that. Here's how three common types of end terminals work—or are supposed to:

1. ET-Plus

Chris Philpot

The guardrail-end treatment at the center of the controversy is a device called ET-Plus. It has a blunt face that caps the end of a W-beam guardrail. Developed by the Texas A&M Transportation Institute (TTI) and produced by Trinity under license, the ET-Plus is a flat steel plate that is designed to slide along the W-beam upon impact, absorbing energy and guiding the rail away from the vehicle in a flat ribbon. The concern is that the new, narrower design might prevent the end terminal from traveling along the rail, and that it would instead bind up and impale cars.

2. Slotted Rail Terminal

Chris Philpot

The Slotted Rail Terminal, also developed by TTI, uses horizontal gaps in the W-beam itself that effectively divide the beam into four sections. Upon impact, the beam bends out of the way in a controlled manner, absorbing energy.

3. Wyoming Box-beam End Terminal

Chris Philpot

The Wyoming Box-beam End Terminal system uses a series of square box-sections instead of W-beams that collapse over one another to absorb energy.

But the best guardrail is always the one that's never used. "You don't want to indiscriminately line roadways with guardrail," says Roger Bligh, a civil engineer with TTI. "If there's a reasonable runoff recovery area out there, then we want a driver to have that opportunity rather than striking a guardrail. We generally use a guardrail only when striking it is going to be less severe than striking another obstacle or hazard that might be on the roadside." Today, virtually everything along major roads, from the slope of drainage ditches to the presence of cushions and breakaway signage, is designed to put the driver back in control of his vehicle long before he hits a guardrail. But if you have to hit one, it's still best not to do so end-on.

John Cooper Fitch: Safety Stud

Glamorous, brave, fast, and gracious, John Fitch was the great American racer. But more important than his wins at Sebring, drives at Le Mans, and development work on early racing Corvettes was his invention of the Fitch Inertial Barrier, those big, yellow impact-absorbing barrels on the highway. They're not just full of sand; voids inside allow the mass to be tailored to control deceleration. The system has saved tens of thousands of lives. Fitch died in 2012 at the age of 95.

Chris Philpot

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