Before the police can pull you over and make you take field sobriety tests or use a breath test, they need to have probable cause. This is part of the law so that officers don't take it upon themselves to just pull over every car, hoping to snag a drunk driver by checking everyone.
So, what do they need to find as probable cause? Of course, the first things they look for are actual signs that you're driving drunk. These include things like swerving out of your lane or failing to maintain a normal speed.
However, many officers know that the odds that they'll find drunk drivers go up after midnight. Therefore, they may decide use other things to justify the traffic stop. They can then see if you seem drunk—or if they smell alcohol—when they talk to you. Other things that legally justify pulling your car over include:
1. Driving with one or more of your lights out. These can be either headlights or taillights.
2. Driving a vehicle with obvious damage or defects that could make it a hazard on the road, a vehicle that is unsafe to drive.
3. Not coming to a complete stop at a stop sign or a red light. This is known as making a rolling stop.
4. Driving over the speed limit.
5. Driving without the proper registration sticker on your license plate, or driving with any sort of obstruction over your plate.
If you're pulled over on these grounds and then given a DUI, you need to know your legal options in Maryland.
Source: Motorists.org, "How To Protect Your Rights During A DUI Traffic Stop," accessed Jan. 08, 2016