Recently, California lawmakers were presented with a proposal that may have made convictions for driving under the influence of marijuana much easier for prosecutors. The success of AB 2500 would have meant that a DUI conviction would be possible if a driver was found to have even trace amounts of the drug in their blood at the time that they operated a vehicle. The new law would have meant that a driver could be completely sober but still be convicted of DUI because they ingested pot days before driving.
The proposal was defeated, in part, because blood tests cannot be conducted by the police in the same way a BAC test can be. The inability to test for marijuana in a suspect's blood at the scene of an arrest makes such a law difficult to enforce. In addition to questions about testing drivers for marijuana, another question must be asked: how much pot must be in someone's system to impair their driving? There is no clear answer.
According to a recent story featured on NPR, many people believe that driving while under the influence of marijuana is much safer than driving while under the influence of alcohol. The science involved in studying the impact of marijuana on driving ability is not definitive. Whether or not alcohol or marijuana is safer is only one issue that is getting increased attention as attitudes and laws regarding marijuana continue to change.