Every time we renew our driver license, the DMV sends us our new license along with a guide from the DMV showing a chart of the BAC (Blood Alcohol Content) percentages. This guide is prepared by the DMV, the CHP, The Office of Traffic Safety, the Department of Alcohol and Drug Programs and the Department of Justice. It states “There is no safe way to drive after drinking. Even one drink can make you an unsafe driver”. It also states that it is illegal to drive with a BAC (Blood Alcohol Content) of .08% or higher. Even a BAC below .08% does not mean that it is safe or legal to drive. In this guide, it also shows that a BAC of .01% to .04% may be charged as DUI, and shows that a BAC of .05% to .07% is likely to be charged as a DUI. A BAC of .08% or higher will definitely be charged as DUI. These BAC percentages apply to drivers over the age of 21 driving a private vehicle that does not require a commercial license. Drivers with a commercial license are subject to an even stricter standard. For those drivers, the BAC limit is .04% while driving a commercial vehicle.
In a DUI trial, prosecutors will use the BAC percentage as chemical test evidence to convict a driver of a DUI. In cases where there is a .05% BAC or lower, the law “presumes” that you were not under the influence UNLESS there is further evidence of impairment such as erratic driving, slurred speech, unsteady gait, or other contributing factors. If these are present, prosecutors will likely charge a driver with violation of Vehicle Code 23152(b). Therefore, prosecutors can also consider a .05% to be "under the influence" even if it has been determined that the driver did not actually reach the requisite .08% BAC level.
It is recommended that all drivers completely abstain from drinking alcohol before driving. The consequences are even more severe for commercial drivers. Even if a driver with a commercial license is driving a non commercial vehicle, and is driving in their own free time, they are still at risk of losing their commercial license.