A Canadian-made transport trailer is being hailed by American safety experts as the gold standard for protecting drivers and passengers of cars that crash into the trailer’s rear.

Dry vans manufactured by Quebec-based Manac and sold under trade names Manac and Trailmobile were the only trailers to pass all three tests of the trailers’ rear underride guards conducted by the Virginia-based Insurance Institute for Highway Safety (IIHS).

The trailers that failed included American trailers built to tougher Canadian standards for rear underride guards, prompting the IIHS to call for standards that more closely approximate the results of the Manac trailers.

Underride guards came into prominence after the death of actress Jayne Mansfield, who in 1967 was riding in a 1966 Buick Electra when it crashed into a stopped transport trailer near New Orleans. The greenhouse of the car was sheared off, Mansfield and the driver died instantly.

The guards, also known as Mansfield bars, transfer the structure of the trailer from deck height down to a level more compatible with cars. Without them, or when they fail, the car can ride under the deck with often-catastrophic results.

“Modern vehicles are built to handle severe frontal crashes,” said IIHS spokesman Russ Rader. “The crash-absorbing structures in the front of the vehicle are designed to crush and absorb impact and keep it away from the passenger compartment. If the car engages with the underride guard, and the guard stays in place, the front of the car crushes like it would hitting any other vehicle and people could walk away from a crash like that. But if the guard gives way and the car slides under the vehicle, then all bets are off. And you’ve missed all the important safety features in the front of the car. With the stronger Canadian standards, as we’ve seen, these kinds of underrides can be prevented,” Rader said.

The IIHS tested the bars in full-width crashes, 50% overlap (where the end of the bar is at the centre of the car) and at 30% overlap, the toughest standard. (The IIHS chose 30% because that was the minimum amount of impact that could still result in the trailer striking the head of the occupant on the side of impact).

A 2010 Chevrolet Malibu was used for all tests, chosen because it is has earned the institute’s Top Safety Pick. Using a Top Safety Pick helps ensure the results reflect flaws in trailer design rather than flaws in the test vehicle’s safety mechanisms.

All trailers tested passed a full-width impact, sufficiently transferring crash forces to the structure of the trailer and allowing the car’s crush zones to properly protect the passengers. All but one, those build by Vanguard, passed the 50% overlap test and all but the Manac trailers failed the 30% overlap test (see chart for complete results).

The Manac trailers passed, according to the IIHS analysis, because the vertical supports that hold the bars near car bumper height are attached more closely to the outside of the trailer and to a reinforced mounting position on the trailer deck.

The typical failure resulted from horizontal bars that bent outside the vertical supports or those where the vertical support on the side of impact failed.

“What we’re trying to do is encourage the transportation industry to purchase the trailers that meet the tougher standards,” Rader said.

Bob Dolyniuk, executive director of the Manitoba Trucking Association, said the trucking industry keeps safety as a top priority, but wonders about the fairness of offloading additional equipment costs to truckers on an issue that rarely, if ever, is the trucker’s fault.

“It’s affecting our industry’s equipment costs because of the need to prevent people from hurting themselves,” Dolyniuk said. “We’re not opposed to safety. But we’d like to see some responsibility on the other side.”

“Almost all motor vehicle crashes involve drivers making mistakes, but the sentence for a mistake shouldn’t be death,” Rader countered. “Our tests demonstrate that underride in crashes can be prevented with relatively inexpensive changes to the guards on trailers. Manac made a change that added 20 lbs to the guard and cost about $20.”

Still, Dolyniuk would like to see some action by vehicle manufacturers and governments to increase the training and examination standards of drivers of passenger vehicles. It’s an issue that goes beyond underride guards and covers all aspects of how vehicles share the road.

Dolyniuk said too few passenger car drivers understand the dynamics of truck-trailer combinations, specifically, the trucker’s ability to begin moving and to stop moving. He said more work needs to be done to help drivers understand how to interact safely with transport trucks on the roadway.

David Zuby, chief research officer for the IIHS, said in a press release that a benefit to the industry from stronger underride guards is that after a crash, the underride guard is often the only part of the trailer to require repairs, helping mitigate crash costs.

“If trailer manufacturers can make guards that do a better job of protecting passenger vehicle occupants while also promising lower repair costs for their customers, that’s a win-win,” Zuby said. “While we’re counting on NHTSA to come up with a more effective regulation, we hope that in the meantime trailer buyers take note of our findings and insist on stronger guards.”