Why put rear underride protection on trailers but not Single Unit Trucks? Any underride is deadly.

I ran across a study on underride fatality crashes this morning. I’d read it before but took a lot at it again. +

Then, this afternoon, while in city traffic, I saw an almost-side underride-crash between a car and Single Unit Truck (SUT). And when I arrived at a parking lot later, I saw a wimpy rear underride guard on a SUT.

So, why do we put rear underride guards on trailers but don’t require them on SUTs? (Not even mentioning that the current rear guard requirement is ineffective as written.) And why don’t we require side underride guards on any large trucks?

Truck underride is deadly no matter the truck size or portion of the truck the smaller vehicle rides under.

Trip North May 2015 033underride guards trip to RDU 007

SUT Underride guard Great Dane trip 061

+ For SUTs, the study showed that, “Considering all degrees of underride, trucks with a guard suffered slightly more underride than trucks with no rear-end protection, 69.5% to 66.7%. . . This result is counter to what would be expected, although it may be due to small, sample sizes and a host of other complicating factors. The severity threshold of the TIFA file may serve to decrease variation in the amount of underride by rear-end structure, since a fatality must occur for the crash to be included in the file. It could be that many of the collisions are beyond the design limits of the guards, and so the guards have no effect.” Underride in rear-end fatal truck crashes, Submitted to National Highway Traffic Safety Administration, prepared by Daniel Blower Kenneth L. Campbell, The University of Michigan Transportation Research Institute, October 1999

In other words, the wimpy guards aren’t effective anyway, so even if a SUT has one, the guard usually doesn’t do what it’s supposed to do — which is to prevent deadly underride.

Current rulemaking on underride protection for SUTs is in limbo at NHTSA: ANPRM Underride Protection of Single Unit Trucks

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