Soap Lake Posse
This has all been looked at. Each state has a legal level where a driver is considered impared from marijuana use. The blood work although not quite as clear cut as alcohol does give a more accurate picture then what you are implying imho by looking at active THC.Considering how long THC can be detected in one's system it would definitely make sense that its the one most often found after fatal crashes.
Then again just because its detected in a test doesn't really prove that much. A fat guy like me can fail a test several months after smoking. I know this first hand. So in theory I could smoke heavily at home on my couch for months on end, sober up for a month, get in a fatal car