> But then as soon as you put a cost associated with saving a life, the whole idea of safety first goes out the window. In this case, underrides are clearly avoidable and really don't cost that much to prevent. Retrofitted truck solutions are available, cheap, and easy to install.

There's a reasonable argument to not even bother with retrofitting. This has been a known issue for decades, just start building it into new trailers, and eventually the old trailers will age out and/or become uninsurable.