Underride: Still looking for Mr. Goodbar

June 1, 2011
KEEP that underride test stand handy. Another round of rear impact guard regulations may be on the way. The budget that the National Highway Traffic Safety

KEEP that underride test stand handy. Another round of rear impact guard regulations may be on the way.

The budget that the National Highway Traffic Safety Administration recently submitted to the House Appropriations Committee calls for increased vehicle safety research, including testing of “advanced underride guards for heavy trucks.”

In its “Budget Estimates Fiscal Year 2012,” NHTSA seeks funding for nine projects associated with vehicle safety systems research and analysis. Overall, the agency is asking for $8,376,000, up slightly from the current fiscal year. A new test program involving advanced underride guards for heavy trucks is the second bullet point on that list.

The underride research project is one of four new proposals in the area of vehicle safety systems. Others include head restraints, vehicle-to-vehicle communication technologies, and occupant protection systems. The rest of the requests are extensions of research projects that are already under way. Examples of these include child restraints and dynamic rollover test procedures.

A review of FMVSS 223 and 224 is clearly on NHTSA's radar screen. Late last year, the agency requested comments on a technical report titled “The Effectiveness of Underride Guards for Heavy Trailers.” The report analyzed available accident report data and reached this conclusion: We don't really know for sure if they work or not.

There are several reasons why we don't know — all of which involve a lack of data. We lack facts for a couple of reasons:

For one, thankfully, underride fatalities are relatively rare. More than half of the 33,308 fatalities recorded in 2009 involved head-on collisions, with side impacts the second-leading cause of fatalities. Even non-collision accidents such as rollovers and running off the road caused more fatalities (7% of the total) than underride collisions.

Further limiting the research data is the fact that the most widely used database of accident information (the Fatality Analysis Reporting System) does not track trailers by model year. This makes it difficult to know if the trailer involved in the fatality was built before or after 1998, the year NHTSA's underride performance standards went into effect.

Based on limited samples of more detailed reports from North Carolina and Florida, researchers say the guards are working, but the results are not statistically significant.

The Insurance Institute for Highway Safety (IIHS) has taken a much more definite position on the subject and is pushing NHTSA to require significantly stronger guards. The organization's position is based on research of its own — six crash tests in which a car with a five-star crash rating is slammed into the back of a van trailer. Some of the guards met the challenge. In other crashes, the guards yielded, allowing the car to underride the trailer.

One of the central recommendations of IIHS is to substantially increase the strength requirement of the guards and not be concerned about absorbing energy. The current underride regulation mandates that trailer manufacturers produce a guard that is strong enough to withstand specific forces and yet yield enough to absorb energy. NHTSA in effect makes the underride guard partially responsible for managing the deceleration of the vehicle that plows into it.

Some of today's cars earn five-star crash ratings. All perform better than they did 20 and 30 years ago when decisions were being made about what an underride guard should be able to do.

The priority in designing an underride guard, the IIHS maintains, should be to stop the vehicle. The automobile's energy management system should protect the occupants from rapid deceleration. As it stands now, at least according to the IIHS research, it may be possible for a guard to comply with the current safety standards but still allow the car to underride the trailer.

Ironically, before the current regulations went into effect, TTMA had a recommended practice for underride guards that closely resembled what NHTSA eventually implemented. The big difference was that it did not address energy absorption. As TTMA president Jeff Sims recalls, the energy absorption requirement was a surprise addition that was not included in the original notice of proposed rulemaking back in the mid-1990s. Now it turns out that energy absorption may not be as important as it once was.

NHTSA says it will assess research data and decide on where the issue goes from here. The next milestone: an agency decision in 2012.

About the Author

Bruce Sauer | Editor

Bruce Sauer has been writing about the truck trailer, truck body and truck equipment industries since joining Trailer/Body Builders as an associate editor in 1974. During his career at Trailer/Body Builders, he has served as the magazine's managing editor and executive editor before being named editor of the magazine in 1999. He holds a Bachelor of Journalism degree from the University of Texas at Austin.