The thin pieces of metal hanging below a big rig is all that prevents you from plowing underneath a truck in an accident.

New research by the Insurance Institute for Highway Safety finds that the underride guards on semi trailers are safer than ever. However, real-world statistics hint that the improved parts might not be saving lives.

In the latest round of tests, the trailers from Great Dane, Manac, Stoughton, Vanguard, and Wabash passed all three of the the institute’s evaluations and earned the IIHS’ Toughguard award for the companies. The agency checks how much punishment the underride guards can take by launching a vehicle going 35 miles per hour into their full width, 50 percent of their area, and the 30 percent at the end. Each test is more difficult than the last because the protective pieces have to withstand a greater force.

The trailers from Hyundai Translead, Strick, and Utility passed the first two evaluations but failed the 30-percent test. According to the IIHS, these companies will work on improving the designs, and the agency will check them again after the upgrades.

IIHS Underride Test

The underride guard hangs below the rear of a semi truck and is supposed to stop a car from plowing underneath the truck during a crash, and the United States government mandates certain safety requirements for the parts. All of the examples in this evaluation apply to the rules, too. However, the IIHS, an insurance-company-funded group, found that the standards allowed the protective aids to buckle or break in come crashes. It stated conducting independent tests of the parts in 2011.

"IIHS isn't a regulatory agency, and other than safety, there was no incentive for semitrailer manufacturers to make improvements," David Zuby, the Institute's executive vice president and chief research officer, said in the announcement. "When we started testing, we weren't sure how they would respond. These companies deserve a lot of recognition for their commitment to addressing the problem of underride crashes."

U.S. Government data isn’t showing that rear-end accidents with semis are any safer, though. The Feds don’t specifically monitor underride crashes, but the death toll from hitting the back of big rigs is on the rise. These types of accidents caused 260 deaths in 2011 and rose to 427 fatalities by 2015 – a 39 percent increase. In the same period, the overall loss of life from incidents with semis are up 15 percent from 2,241 incidents in 2011 to 2,646 cases in 2015.

Truckmakers are trying other methods to improve safety, though. For example, Samsung has an experimental rear-mounted display for letting drivers see what’s happening in front the truck. In the future, autonomous trucks like Otto could remove the human element from the profession, too.

Source: Insurance Institute for Highway Safety

More from IIHS:

Be part of something big