At various times, members of the trucking industry have voiced doubt about the ability of side guards to function effectively in “real world” crash scenarios.

“We have yet to see evidence that side underride guards would be an effective safety countermeasure,”  American Trucking Associations   Vice President of Public Affairs and Press Secretary Sean McNally said. “Until these devices can be shown to be reliable outside the test track, we believe Congress and regulators should focus on reducing crashes by addressing aggressive and distracted driving and investing in existing, proven safety technologies, including emerging connected vehicle technology.

ATA also notes that trucking companies have opposed the legislation because it “promotes a solution that is neither data-driven nor proven to be effective in real-world highway settings,” and entails potentially “dangerous” and “unintended” consequences. Congress takes third swing at side underride bill

For this SAE research, Protecting Passenger Vehicles from Side Underride with Heavy Trucks, the authors carried out computer simulation in order to assess how side guards would operate in various conditions. According to Garrett Mattos, the principal author,

• We simulated angles (0 degrees, 30, 60, and 90 degrees). 
• We simulated sliding (as if on ice).
• We simulated both stationary and moving truck. Slightly worse outcomes for moving truck vs stationary truck.

Garrett Mattos presented an overview of the research paper at the Side Guard Task Force Meeting on February 26, 2021. You can see his presentation at 1:46:21 on this YouTube Video:

ABSTRACT

Impacts between passenger vehicles and heavy vehicles are uniquely severe due to the aggressivity of the heavy vehicles; a function of the difference in their geometry and mass. Side crashes with heavy vehicles are a particularly severe crash type due to the mismatch in bumper/structure height that often results in underride and extensive intrusion of the passenger compartment. Underride occurs when a portion of one vehicle, usually the smaller vehicle, moves under another, rendering many of the passenger vehicle safety systems ineffective.

Heavy vehicles in the US, including single-unit trucks, truck tractors, semi-trailers, and full trailers, are currently not required to have side underride protection devices. The NTSB, among other groups, has recommended that side underride performance standards be developed and that heavy vehicles be equipped with side underride protection systems that meet those standards.

The work presented used virtual testing to evaluate the relative performance of example side underride devices compared with a baseline. Crash test results were utilized for validation purposes. A tractor-trailer, with and without side impact underride protection, was impacted by a passenger car and SUV under a range of impact conditions. Passenger vehicle intrusion metrics were calculated to provide an indication of relative risk for each impact condition. The results can support the development of side underride protection recommended practices.

DISCUSSION

The results of the analysis indicate that available side underride guards are effective at reducing passenger compartment intrusion (PCI) substantially in what are often fatal side underride crashes. Nearly all passenger compartment intrusion above the beltline was mitigated other than in the purely lateral impact conditions. When intrusion did extend above the beltline, e.g. in the purely lateral sliding condition, the amount of PCI was similar to the intrusion generated in a 56 km/h side impact of a 5-star rated vehicle. Further, the average amount of PCI in the above tests was similar to the amount resulting from small overlap tests of the same vehicle. These results demonstrate that an underride guard can provide a sufficient reaction surface to allow for the vehicle’s passive and active safety systems to protect the occupant. The underride guard also causes the location of PCI to move from near the occupant’s head and torso to the lower extremities which reduces the likelihood of serious or fatal injury.

In general, the results suggest that impacts with a moving truck/trailer combination are more severe than when the truck is stationary. The added velocity of the truck/trailer combination results in greater intrusion of the bullet vehicle firewall as well as slightly higher peak accelerations. Impact severity was also increased when the size of the gap between the end of the underride guard and the rear tires was increased. The increased gap size allowed the bullet vehicle to interact more with the rear tires. In the impacts with a large gap the trailer tires very nearly engaged the driver side door. These results can help to define a comprehensive test plan that can be used to assess the performance of an underride guard.

The acceleration pulses for all impacts were within the range of frontal and side impact crash test pulses generated in similar tests of vehicles that exhibit 5-star safety ratings. This indicates that these impacts were all survivable. The most severe impact scenario was a 56 km/h sideways slide into the trailer with an underride guard.

As shown, there is an 80% or greater reduction in PCI for impacts with an underride guard compared to the baseline condition. Additionally, the location of PCI in the underride guard impacts was generally found to be at the outer firewall area rather than at or above the belt line as in the baseline case. Reducing the PCI and moving the location of PCI away from the occupant’s head and torso both significantly reduce the likelihood of serious injury. No adverse effects were observed as a result of the underride guard.

These results indicate that tests used to evaluate the performance of underride guards should incorporate a moving truck/trailer combination as this was found to increase the severity of the impact. Additionally, the location and size of gaps between an underride guard and the trailer tires and/or landing gear should also be considered as this was found to affect the results. The results demonstrate, along with other work in the literature, that Finite Element analysis can enhance physical tests to expand the number of impact scenarios in a cost-effective and time-efficient manner. While additional impact conditions and test cases can be analyzed, the results are expected to further demonstrate the importance of trailer side underride guards in reducing passenger compartment intrusion under these crash conditions.

Side underride guards integrated into the trailer structure may further enhance the safety benefits associated with preventing trailer underride and limit added weight. Exploration of these design alternatives should be explored in the future in conjunction with additional crash vehicles and configurations.