The National Highway Transportation Safety Administration (NHTSA) has a publication that lists the "symptoms" of drunk driving officers are trained to watch for in "driving pattern." Each "symptom" has been given a value NHTSA says represents the likelihood a driver exhibiting that driving pattern is under the influence of alcohol or drugs.
Here is the list from the Department of Transportation Publication (DOT HS-805-711) used to train law enforcement officers to identify intoxicated drivers:
Turning with wide radius 65
Straddling center or lane marker 65
Appearing to be drunk 60
Almost striking object or vehicle 60
Weaving 60
Driving on other than designated roadway 55
Swerving 55
Slow speed (more than 10mph below limit) 50
Stopping (without cause) in traffic lane 50
Drifting 50
Following too closely 45
Tires on center or land marker 45
Braking erratically 45
Driving into opposing or crossing traffic 45
Signalling inconsistent with driving actions 40
Stopping inappropriately (other than in lane) 35
Turning abruptly or illegally 35
Accelerating or decelerating rapidly 30
Headlights off 30
So here is how this works – if an officer sees you driving into opposing or crossing traffic, NHTSA educates officers that 45 times out of 100, the driver (you or me) is operating under the influence. It doesn’t matter the time of day, or the day of the week, NHTSA trains officers to believe that this stuff is "science.