A Maryland law enforcement officer cannot pull over your vehicle unless he or she has witnessed you violate a traffic law or has reasonable suspicion to believe that you are operating the vehicle under the influence of drugs or alcohol. Because the law classifies reasonable suspicion as less than probable cause, a range of driving behaviors can result in a legal traffic stop. 

These are the common circumstances that may establish reasonable suspicion for a traffic stop that could lead to a DUI arrest. 

Speeding or driving too slowly 

If you travel at least 10 miles below or above the speed limit, the officer can legally stop you. If you need to slow down because of an issue with your vehicle or because you are not sure where you are going, it is best to pull over completely instead as long as it is safe to do so. 

Drifting and unsafe lane changes 

You can receive a ticket for crossing over the double yellow line in no-passing zones, even if you only drift across for a second. If you change lanes unsafely, that action can also serve as grounds for a legal traffic stop. Although it is not illegal to switch lanes frequently, the officer could argue that you were weaving, making suspicion of DUI reasonable. 

Following too closely 

If you are driving without enough stopping distance behind the vehicle in front of you, an officer can legally stop you. As a general rule, try to stay at least one car length or 10 feet for every 10 miles per hour that you travel. 

Vehicle issues 

Even when you are driving safely, an officer can stop you for a problem with your vehicle. If your headlight has burned out or if your tires are a bit low, correct these conditions before you get on the road. 

During a traffic stop for any of these issues, the smell of alcohol can serve as legal suspicion for a DUI arrest. You must take a field sobriety test if asked to do so or potentially face additional court penalties.