Police officers are trained on what to look for when deciding whether to pull you over for suspected drunk driving, and understanding why the officer stopped you can help you be better prepared to make decisions about your defense strategy. Officers usually suspect a driver of operating under the influence based on observations while the vehicle is moving.
Reckless driving is one indicator of an impaired driver, as alcohol and other substances can alter your ability to make good decisions while driving. Drivers may speed up or slow down quickly or without apparent reason, drive to close to the car in front of them or turn without signaling or slowing down. In extreme cases, the driver may even be driving on the wrong side of the road.
Weaving and drifting across lane lines are also classic signs of an impaired driver, as is driving in the middle of the road. Impaired drivers may have difficulty judging how close they are to going on to the shoulder and, therefore, drive in the middle to avoid going off the road. Running into or glancing other cars, curbs or stationary objects is another common sign that officers look for.
Impaired drivers may also try to avoid a traffic stop by turning off their headlights at night or driving well below the speed limit, but officers are trained to spot these indicators as well. If the officer conducting the traffic stop believes you to be driving under the influence, you will most likely be given a field sobriety test and then arrested on suspicion of DUI.
Source: MADD, "How to Spot a Drunk Driver," accessed April. 16, 2015