When an officer is on patrol, he may have as part of his assignment to be on the lookout for drunk or otherwise impaired drivers. Normally, officers who are given this task have been specially trained in DUI enforcement through the Mississippi Law Enforcement Officers Training Academy (MLEOTA) in Pearl. If they were not trained at MLEOTA, they typically received DUI enforcement training somewhere. And almost always, the training any officer receives is based upon standardized DUI educational materials authored by the National Highway Traffic Safety Administration (NHTSA), which is part of the United States Department of Transportation.
The standard DUI training from NHTSA covers everything from an officer’s first view of a car in motion through arrest and reporting. The first part NHTSA covers is “vehicle in motion” observation.
Vehicle in Motion
When an officer sees a car moving down the roadway, he is taught to look for clues that its driver might be impaired. There are four categories of clues that officers are taught to look for to detect potential driver impairment, along with examples the officers are given:
- Problems in maintaining proper lane position
- Weaving
- Crossing lane lines
- Drifting
- Straddling a lane line
- Swerving
- Nearly running into another vehicle or object
- Turning with a wide radius
- Speed and braking problems
- Stopping too short or too far
- Braking in a “jerking” fashion
- Unnecessary speeding up or slowing down
- Varying speed
- Driving 10mph or more under the speed limit
- Vigilance problems
- Not turning headlights on at night
- Failing to use turn signal or using it incorrectly
- Driving in the wrong lane (against traffic)
- Stopping for no apparent reason
- Judgment problems
- Following too closely
- Improper lane change
- Illegal turn
- Driving off of the road
Officers are taught that some of these clues are more indicative of DUI than others, but that the presence of any single one of them means there is a 35% chance the driver is impaired. For example, NHTSA says that weaving across lane lines means there is a 50% chance the driver is impaired, while swerving (an abrupt jerking of the car into another direction of travel to correct drifting) means there is a 70% likelihood of impairment. When any two clues are combined, the officers are taught that there is at worst a 50% chance that the driver is impaired.
Officers only need probable cause (generally defined as more likely than not, or more than 50% likely) to believe a driver is impaired to initiate a traffic stop. So if they see a vehicle swerve, or if they see a driver follow too closely and then change lanes without using a signal, they will feel confident that they can stop the driver under suspicion of DUI.
If the officer decides to stop the car, he or she then watches the way in which the driver stops the car for more clues of impairment. They are taught to watch for the following:
- Trying to flee
- No response to the blue lights or a slow response
- Abruptly weaving
- Sudden stop
- Hitting the curb while stopping
- Any new traffic violation
This first phase, Vehicle in Motion, is an important evidence gathering phase for the officer, who is building his DUI case from that very moment. If you wind up charged with DUI, you can expect to see some of the above referenced in the officer’s report. The next phase is when the officer first interacts with the driver, which you can learn more about in Step 2 – First Contact with Law Enforcement.