Kiro has done an interesting video on Marijuana and DUI. Many people believe the legal limit for Marijuana is far too low; some of the driving in this test performed by the news crew seems to suggest that might be true. Here's a link to the full article and the video:
http://www.huffingtonpost.com/2013/02/18/stoned-drivers-test-course-marijuana-dui_n_2711358.html