As far as I can tell, recreation pot was legalized in Colorado effective September, 2013, so that would have no impact on the stats from 2007 to 2012.
The choice of 2007 and 2012 looks highly selective. Maybe 2007 was abnormally low.
The whole point is that legalization is not going to improve those numbers. It's not okay to drive stoned any more than it's okay to drive drunk, or on Ambien, and anything else that impairs common sense.
I have an ex named Michelle who now thinks it's perfectly ok to drive down the road smoking a pipe full of weed because it's legal now in Colorado. She didn't before because weed was illegal. She's a lousy driver when she's straight and weed will not improve her skill.
Bottom line here - smoke it all you want at home just stay the f&%k off the road!