For many of those who are arrested on suspicion of a DUI, the traffic stop doesn't even start because they are impaired. It starts because of some other driving error that was made, giving the police a reason to pull the car over -- and, perhaps, probable cause to suspect that the driver is drunk. It's only after the stop is made that the officers realize alcohol really may be an issue.
For example, one person swerved out of his lane and was pulled over by police. He'd admittedly had a few beers, but he said that wasn't the reason for the swerve. Instead, he claimed his car pulled to one side naturally, and he'd looked away from the road to text his girlfriend.
It didn't matter. He was still pulled over on suspicion of drunk driving. It's critical for all drivers to know that police can legally pull them over for a whole host of reasons, and any one may be enough to start a DUI stop.
That being said, it is important to note that police cannot stop you randomly just to check and see if you've been drinking. They have to establish probable cause first, in one form or another. This prevents police from simply targeting random drivers who haven't made any mistakes, just because they're driving after the bars close for the night.
Do you think the police had no right to pull you over? If so, whether you'd been drinking or not, you may be able to argue that the initial stop was illegal and all evidence obtained has to be thrown out of court. It's important to know your legal options, to understand why traffic stops are really made, and to be sure your rights weren't violated.
Source: Quick and Dirty Tips, "What to Do if You are Pulled Over for DUI," Adam Freedman, accessed Dec. 01, 2016