When the officer is following the vehicle there are a variety of different erractic or abnormal behaviors that an officer will look for. The most common is to see if the vehicle is swerving or crossing over the painted lines on the road. This does not necessarily mean that vehicle is wildly swerving and careening back and forth. Many times it’s the little things that will give a drunk driver away. For example, a vehicle may cross the line on the right side of the road enough that the tire is on the other side of the line. This one cross alone is generally not enough to constitute a traffic stop because even a sober driver from time to time will make this mistake. What the officer is looking for however is how many times the driver repeats this action in a short amount of time driving a short distance. The exact amount of time is hard to say exactly because it may depend in the given circumstance, but generally speaking the shorter the amount of time and distance the greater the chances the officer will stop the vehicle to investigate further.
Another action an officer will watch for is erratic speeds of the vehicle. If a driver starts out going 50 MPH, but then slows to 30 MPH and then increases speed again, this will peak the officer’s interest because this is not a behavior that is normal when operating a vehicle. Generally the officer will further observe the vehicle to see how many times this happens and look for further indicators.
Officers are looking for any vehicle maneuvering that is abnormal or erratic as compared to how the average sober driver handles his vehicle. The most common being vehicle swerving which as examined above does not necessarily mean an abrupt or huge swerve. In some cases an officer may not feel like there is enough erratic behavior to justify stopping the vehicle on that alone and will look for another reason to stop the vehicle to investigate further.
