Well-known California DUI lawyer Lawrence Taylor is now challenging whether DUI can be applied to marijuana usage. 


Taylor is questioning whether marijuana impairs a person's ability to drive to the degree alcohol does. While there have been various tests regarding alcohol-impairment in driving, there are relatively few to support the same is true of cannabis. 


The California Department of Justice has produced studies showing marijuana impairs the motor abilities that are needed for driving. This mostly occurs at high doses or among young, inexperienced drivers. Taylor is citing federal studies that contradict these findings.


One such study performed by the U.S. Department of Transportation researched the topic using a simulator to compare the affects of alcohol and marijuana, both separate and when combined. Alcohol created impairment across the board, while marijuana only occasionally impaired drivers. 


Another study cited claims that cannabis, or THC, is not "profoundly impairing." Some information processing skills are impaired, but not to the ability that a person cannot control driving, according to the study. 


A further issue over marijuana DUI laws is the fact that the drug is metabolized quickly but can stay in the body for hours or days. Traces of THC will remain in the body for weeks. Measuring these levels in blood tests may point to chemicals that have been in the body for days. 


It would be difficult to prove a person was significantly impaired by marijuana at the time of an arrest for these reasons. First, marijuana only occasionally creates significant impairment, according to federal studies. Second, testing for marijuana use cannot pinpoint if and when the person was actually affected by the drug, only that it is in his or her system.


Laws in California are further complicated by the legal use of medicinal marijuana. Not every person who is found with marijuana in his or her system has even committed a crime. Some may have prescriptions for use of the drug, making the crime in effect no different than driving after taking anti-anxiety or anti-depressant medication.