There are different types of DUI charges and different legal limits for DUIs. In Los Angeles County, the standard way a driving-under-the-influence case is charged is with two separate charges or two counts. Additionally, you have a case with the Department of Motor Vehicles. The two charges typically filed for a DUI in Los Angeles would be 1) driving under the influence of alcohol and/or drugs and 2) driving with a blood alcohol level of 0.08 or more. This means that the prosecutors are going to try to convict you of being impaired or basically drunk driving, and they are going to try to convict you of having a blood alcohol level that is over the legal limit.
If the blood alcohol level can be shown scientifically at 0.08 or above, they will try to get a conviction solely on that. The charge for driving under the influence of alcohol and/or drugs leaves a lot of wiggle room for prosecutors. There even are certain prosecuting agencies in Los Angeles that will try to get convictions of people when their alcohol level is below a 0.08. The first way to do that is by saying that the individual was impaired. The other is by saying that, mathematically or scientifically, the individual was over the legal limit. Either one could result in a conviction.
California has broken up the way DUI cases are charged by separating them into multiple subdivisions. There are separate charges for driving under the influence of alcohol, driving under the influence of drugs, and driving under the influence of both alcohol and drugs. Of course, there is still a charge for driving with a blood alcohol level of 0.08 or above. The state has done this in order to keep better track of how people are being convicted and what they are being convicted of. This all goes back to money because they want to know where to spend the money and how to obtain more money for the court systems and for the states. The National Highway Traffic and Safety Administration and the federal government want to know how to distribute grants. They want to know what types of charges there are.
The complexity of the law concerning DUIs even allows for someone with a blood alcohol level below 0.08 to be charged. Right now, California Vehicle Code 23-152 (A) does not point to a particular blood alcohol level. Someone could be at a 0.06 or 0.05, well below the 0.08 level, and still be charged with a DUI. There are prosecutors that will charge an individual at a 0.05 or 0.06. They will try to prove that according to the driving and field sobriety testing, a particular person was too impaired to drive, even though the individual is not at or over the legal limit.
There is also the real possibility of people being charged with driving under the influence of a combination of both alcohol and drugs. More and more recently, we see people charged with driving under the influence of both marijuana and alcohol. You could have very low levels of marijuana in your system and very low levels of alcohol, prompting prosecutors to say that the combined influence of these two substances are causing this individual to be impaired. Whether or not there is science that can back up those arguments, people are still being charged with a crime.