[retroafroman]

You're talking about the 'Mansfield bar'[0], or 'underride bumper' named after a famous case of a celebrity killed by rear-ending a truck.

[0] http://www.sparebumper.com/index.php?act=viewProd&productId=...

[raisedbyninjas]

A lot of underride guards are still capable decapitating people at low speeds. http://www.iihs.org/iihs/news/desktopnews/underride-guards-o...