With states having a hodge-podge of laws relating to the legality of marijuana possession it's no surprise that states also lack consensus on when it's unlawful to operate a motor vehicle after using marijuana. In one-third of the states a person can be convicted if he or she has any detectable trace of THC in their system ("zero tolerance") or exceeded a certain level of THC in the bloodstream ("per se") even though the defendant showed no signs of impaired driving ability. Maryland Judge Neil Axel, ABA National Judicial Fellow for Highway Safety, joins host Richard Ginkowski for a discussion of the constitutionality of these "zero tolerance" and "per se" laws.