Under California Vehicle Code §23152, it is unlawful to be operating vehicle while under the influence of drugs, alcohol or both. In order for a person to be charged, prosecutors simply have to have reason to believe that a person is guilty of driving under the influence. However, for a person to be convicted of a DUI, prosecutors must prove, beyond a reasonable doubt, that the person being charged was not only driving, but was also intoxicated at the time he or she was driving. Both elements must be present, if there is only one, then the person cannot be found guilty of a DUI.
It is easier to demonstrate in a court of law that a person is under the influence of alcohol while operating a vehicle, than it is to prove the influence of other drugs. Alcohol can easily be tested for, and detected in a bloodstream. This is why when officers believe a driver is under the influence of alcohol, they will administer a breathalyzer test, or a blood test. The test will often provide accurate results as to the amount of alcohol in a person’s blood stream. Based on date, the legislature has even been able to quantify the amount that would qualify as intoxicated.
The use of drugs, specifically marijuana, is a lot harder to demonstrate as a blood test or breathalyzer will not provide an accurate calculation of intoxication. Even if there is marijuana present in a person’s system, it could have been from a day before, and the person may not be under the influence.