The last test of a roadside barrier's ability to contain a runaway tractor-tanker fully loaded to 80,000 pounds took place in Texas more than three decades ago.
Since then, the Manual for Assessing Safety Hardware, yes MASH, Test Level 6 standard called for concrete barriers 90 inches tall to capture and contain a tanker truck traveling at highway speeds.
On Wednesday, researchers at the University of Nebraska-Lincoln's Midwest Roadside Safety Facility proved a shorter, thinner barrier could match the larger one's performance, potentially resulting in the first change to the national standard in several decades.
Getting to that point took a decade of work by facility director Ron Faller and a team of researchers, including Cody Stolle, Joshua Steelman and graduate students.
In addition to designing the new barrier, they ran it through computer models and built a functioning prototype at the center's Outdoor Proving Grounds, located on the west side of the Lincoln Airport.
The years of labor culminated in hooking up a tank filled with 7,000 gallons of water to a 2010 Freightliner Columbia and speeding it directly into the barrier.
“What we saw in this particular case, was everything we predicted would happen, happened,” said Stolle, an assistant research professor. “The work from our students and engineers was phenomenal. It was exactly on point.”
At the moment of impact, the tractor-tanker rolled on top of the barrier and performed a brief skid -- envision a skateboarder riding a rail -- before it was redirected back onto the road, before eventually rolling onto its side.
In less than 1 second, a bevy of instruments -- accelerometers on the vehicle, strain gauges inside the barrier system and high-speed digital cameras -- captured enough data to begin assessing the UNL design.
With the barrier standing just 62 inches tall, 22 inches wide at its base and 10 inches wide at its top, computer models showed it would “upright the vehicle and prevent it from potentially dangerous outcomes” like a tank rupturing or crossing into oncoming traffic or careening off a bridge, Stolle said.
The barrier’s performance capturing a vehicle that collided with it an angle of 15 degrees traveling 50 mph -- an uncommon combination in most crashes -- indicates it would be successful at other speeds and angles as well, Stolle added.
Typically, at higher speeds, the angle of impact is not as steep. The smaller the angle of impact, the less likely a tractor-tanker is going to roll over the barrier.
“This barrier itself should be able to handle both higher speeds at lower angles and lower speeds at higher angles,” he said. “We call it the practical worst case: Not the boundaries of the possible, but the boundaries of the 95% probable.”
By Wednesday night, the Midwest Roadside Safety Facility expected to start poring over data and examining video footage with the goal of bringing the results to state departments of transportation.
Over the next year, the new design tested Wednesday at the Outdoor Proving Grounds could be installed on interstates and highways throughout the country.
“We have state departments interested in installing it if the results today are determined to be successful,” Stolle said. “This outperformed my expectations in terms of capture.”