Through testimony and evidence - just like any other case.
Simply "clipping" a yellow line is not going to be evidence of impairment beyond a reasonable doubt. What he said was that he knew of someone convicted with a low BAC ... a low BAC does not mean someone is not impaired. Alcohol impairment begins at as low as .02. Some people are clearly and objectively impaired at .03 or greater, others not so much. My wife is clearly impaired at about .04. People on medication are impaired at .00. As a result, we have to make a stronger case to convict people who have a low or no BAC ... at least until there is per se chemical testing for controlled substances in all the states.In some cases it is obvious. But I quoted above a claim from Speedy Gonzales that someone was convicted of DUI simply because they clipped a double yellow line, something that can and does happen to sober people every day.
Sorry, but the law has consistently allowed proof from a single witness or investigator. It is up to the trier of fact (a judge or a jury) to weigh the evidence and determine if the burden of proof is met. You may not be "comfortable" with it, but that is and has been the standard for a great many offenses - even felonies!But I'm not comfortable leaving it up to a (single) police officer's word to get a person convicted for a misdemeanor with quite serious consequences.
Sure, it can be! See above ...That is not "beyond reasonable doubt", and we're not talking about a stop sign or speeding 80 in a 65 zone any more.
Well, yeah ... and based upon a quarter century of observation and sharing experiences with officers and court personnel throughout CA on a regular basis. So, I'm pretty confident of it.
There are always exceptions, but that hardly makes it the rule. And many courts (most of those I still attend) will even announce before the trial and after the roll is taken that the court will accept guilty pleas (now that the defendant knows the officer is present) as the option of traffic school MAY not be available after trial.My experience is different, and some of the other folks here share that notion.

