There are normally five kinds of evidence that support a DUI case. The first of these is driving symptoms. This is what caught the police officers attention in the first place. According to the National Highway Transportation Safety Administration (NHTSA) there are 20 of these:
- Turning with a wide radius
- Straddling center of lane marker
- Appearing to be drunk (based on posture, gestures, etc.)
- Almost striking object or vehicle
- Driving on other than designated highway
- Speed more than 10 mph below limit
- Stopping without cause in traffic lane
- Following too closely
- Tires on center or lane marker
- Braking erratically
- Driving into opposing or crossing traffic
- Signaling inconsistent with driving actions
- Slow response to traffic signals
- Stopping inappropriately (other than in lane)
- Turning abruptly or illegally
- Accelerating or decelerating rapidly
- Driving with Headlights off
Speeding however is not one of these symptoms since it requires a high level of coordination.
The second type of evidence is in the driver's behavior and appearance. This includes bloodshot eyes, the smell of alcohol, slurred speech, fumbling for his or her license and registration, and other indications of intoxication. These are recorded in the police report.
The third kind of evidence are field sobriety tests. What many people don't realize is that in most states, these tests are NOT mandatory, they are voluntary. The Standardized Field Sobriety Test (SFST) was developed by the NHTSA. It consists of three tests that should be used in combination with one another. They are:
1. The Horizontal Gaze Nystagmus (HGN) Here the officer moves an object across the suspect's field of vision. This allows the officer to see if the suspect's eyes are moving together and if his or her pupils are the same size.
2. The Walk-and-Turn While counting aloud, the suspect is required to walk nine steps, heel to toe, and turn around and walk back nine steps.
3. The One-Leg Stand The suspect is asked to stand straight with feet together and arms at his or her side. He is then asked to raise one leg off the ground and count aloud for thirty seconds.
The fourth type of evidence is made up of incriminating statements. These statements may be spontaneous or they may be answers to questioning. A suspected drunk driver is not required to answer questions; however, this refusal may be interpreted as incriminating.
The last category of DUI evidence is the chemical test. States vary in the types of tests they use (breath, blood or urine). Blood tests are considered to be the most accurate whereas urinalysis is the least reliable.