Probable Cause for DUI Stop by Law Enforcement
In the United States, police are required to establish "probable cause" in order to stop a vehicle for a potential
drinking and driving offence. The following list of symptoms, from a publication issued by the National Highway Traffic Safety Administration (DOT HS-805-711), is widely used in training officers to detect drunk drivers.
After each symptom is a percentage figure which, according to NHTSA, indicates the chances
that a driver, who displays the symptom, is over the legal limit.
| Symptom | Percentage | Symptom | Percentage | |
Turning with a wide radius |
65% | Following too closely |
45% | |
Straddling center or lane marker |
65% | Tires on center or land marker |
45% | |
Appearing to be drunk |
60% | Braking erratically |
45% | |
Almost striking an object or vehicle |
60% | Driving into opposing or crossing traffic |
45% | |
Weaving |
60% | Signaling inconsistent with driving actions |
40% | |
Driving on other than a designated roadway |
55% | Stopping inappropriately (other than in lane) |
35% | |
Swerving |
55% | Turning abruptly or illegally |
35% | |
Slow speed (more than 10mph below limit |
50% | Accelerating or decelerating rapidly |
30% | |
Stopping (without cause) in traffic lane |
50% | Headlights off |
30% | |
Drifting |
50% |
Probable Cause to Detain
The officer will typically approach the driver’s window and ask some preliminary questions. The purpose is to detect the possible presence of preliminary evidence such as:
- an odor of alcohol on the driver's breath or in the car generally;
- slurred speech in response to questioning;
- bloodshot or reddish eyes;
- flushed face;
- difficulty in understanding and responding intelligently to questions;
- fumbling with driver's license and registration;
- the plain-view presence of containers of alcoholic beverages in the vehicle.
If the officer's observations lead him or her to have a reasonable suspicion to legally justify a further detention and investigation, the driver will be asked to step out of the vehicle.
Field Sobriety Tests
The officer will administer one or more field sobriety tests if alcohol impairment is suspected. The most commonly administered tests include:
- walk-and-turn (heel-to-toe in a straight line);
- finger-to-nose (tip head back, eyes closed, touch the tip of nose with tip of index finger);
- modified-position-of-attention (feet together, head back, eyes closed for 30 seconds);
- one-leg-stand for 30 seconds;
- recite all or part of the alphabet, backwards or forwards.
- touch fingers of hand to thumb in both directions in rapid succession;
- horizontal gaze nystagmus (following an object with the eyes to determine characteristic pupil reaction);
- count backwards from a number such as 30 or 100;
- pick up a coin from the ground without bending down;
- take a breath test to determine individual breath alcohol content (BAC)
BAC does not have to be at or over .08 to establish probable cause for DUI. At the .08 level you are automatically assumed to be DUI. You can be arrested based on other "probable causes" above.
Probable Cause to Arrest
While every state and locality may have different procedures, generally, if the officer has sufficient facts justifying a reasonable suspicion that the suspect has been driving under the influence of alcohol, he will make the arrest, handcuff the suspect and transport them to the police station. En route, the officer may advise them of their rights and his legal implied consent to submit to an evidentiary chemical test of blood, breath or possibly urine.