1. There were product liability cases where there was "joint liability" for "aggravation of injuries" due to the "aggressive design." This was discussed in a recent issue of
Product Engineering. These were not junk cases like the McDonald's hot coffee cases.
2. I have to take issue with your statement that
"It is a rare day when an accident occurs and both people are at fault. That is why there are road rules, to determine who broke them and is at fault." I would suggest that you Google "Failure Mode Effect Analysis" and its alternative name "Fault Tree Analysis" - and search in Dialog and Engineering Index, and download
http://techreports.larc.nasa.gov/ltrs/PDF/2000/spec/NASA-2000-sp6111.pdf (You might even find my published papers from the late 1960's; you will also find some papers by Rasmussen at MIT and McConnaughey at DOT and NTSB and Powers at Carnegie Mellon). There is no such animal as one sole, single cause of an accident, and nobody is ever 100% at fault unless there is actual felonious criminal conduct (not misdemeanor - but felony).