Such signs include driving slowly, weaving, not following traffic signs, etc.
Breathing only becomes impaired from alcohol during alcohol poisoning.
Alcohol intoxication is a state when there is enough ethanol in your body to have an effect - usually the symptoms of euphoria, a certain degree of lethargy, impaired vision, balance, and judgement will be the prime signs of intoxication.
It depends on how aggressive the alcohol-impaired drivers are.
one half....A+
one half....A+
one half....A+
one half
one half....A+
one half
one half
A DUI can still be proven if the officer can show that your driving was impaired. Different people become impaired at different alcohol levels so being below the limit does not 'prove' you were not impaired. The officer may also believe that you were impaired by something other than alcohol. On the bright side, a good defense attorney will be thrilled that you did take the breath test and blew under the limit.