This wreck happened in my neck of the woods this morning. Woman in a Dodge Journey rear ended a tractor-trailer on an on ramp, got stuck and was dragged about 500 feet. Thanks to the under ride bar on the back of the trailer, the woman was alive and conscious at the scene and will probably be fine.

This bar is often referred to as a Mansfield bar because its mandatory introduction on trucks was a result of the gruesome death of actress Jane Mansfield and two others in 1967 (warning, link has some graphic images).

The apparatus below the taillights is the under ride bar.