1. Traffic Safety Facts Research Notes
National Highway Traffic Safety Administration
November, 2014
http://www-nrd.nhtsa.dot.gov/Pubs/812072.pdf

2. Concentrations with Actual Driver Impairment: Practical Limitations and Concerns
Humbolt Journal of Social Relations
NORML (National Organization for the Reform of Marijuana Laws)
2013
http://norml.org/pdf_files/per_se_limits_for_cannabis.pdf

3. Political leaders need to realize there is no evidence for use of per se DUI laws; impairment is the issue 
The Weed Blog quotes The Joint Blog
December 14, 2014
http://www.theweedblog.com/per-se-marijuana-duii-laws-are-based-on-junk-science/12/26/13

4. Health Facts re DUIs
NORML (National Organization for the Reform of Marijuana Laws)
2005
http://www.canorml.org/healthfacts/DUICreport.2005.pdf