and can include observation of actions (erractic lane change) and subjective judgment by an officer to charge. And DWI for driving WHILE INTOXICATED.
The lesser often is how someone is initially charged and becomes the second after blood tests.
me, I'm the kind of person thinks, if you are gonna drink at all, hand over your keys. I don't care if it's a shot, one beer, a glass or half glass of wine over dinner. Call a ride.