DUI PATTERNS
Driving under the influence cases in California tend to follow recognizable patterns. If you understand the most common DUI scenarios, you can spot where the prosecution’s case is weak—and where a defense attorney can create leverage. Below is a practical, real-world breakdown of typical DUI situations and the defenses that actually work.
1. Traffic Stop for Erratic Driving
Scenario:
An officer observes weaving, speeding, braking inconsistently, or drifting lanes. This is one of the most common DUI entry points.
Key Legal Issue:
Was the stop lawful under the reasonable suspicion standard?
Possible Defenses:
- No reasonable suspicion: Minor lane deviations or momentary weaving may not justify a stop. Courts have rejected stops based on vague or subjective observations.
- Alternative explanations: Fatigue, distraction, poor road conditions, or mechanical issues can explain the driving pattern.
- Dashcam/bodycam contradictions: Video often undercuts exaggerated police reports.
Takeaway: If the stop is invalid, everything that follows—including chemical tests—can be suppressed.
2. DUI Checkpoint Arrests
Scenario:
Drivers are stopped at a sobriety checkpoint, often on weekends or holidays.
Key Legal Issue:
Was the checkpoint conducted in compliance with Ingersoll v. Palmer guidelines?
Possible Defenses:
- Improper setup: Lack of supervisory control, no neutral formula for stopping cars, or inadequate safety measures.
- Insufficient signage or warning: Drivers must have advance notice.
- Unconstitutional detention length: Prolonged questioning without cause.
Takeaway: Checkpoints are legal—but only if done correctly. Sloppy compliance opens the door to suppression motions.
3. Field Sobriety Tests (FSTs)
Scenario:
After a stop, the officer administers tests like the walk-and-turn or one-leg stand.
Key Legal Issue:
Are FSTs reliable indicators of impairment?
Possible Defenses:
- Subjectivity: These tests are not scientific. Officers often misinterpret normal behavior as impairment.
- Medical conditions: Injuries, age, weight, or neurological issues can affect performance.
- Environmental factors: Uneven pavement, poor lighting, or traffic distractions undermine reliability.
- Improper instructions: If instructions are unclear, results are meaningless.
Takeaway: FSTs are one of the weakest parts of the prosecution’s case when scrutinized closely.
4. Breathalyzer Results
Scenario:
A roadside preliminary alcohol screening (PAS) or station breath test shows a blood alcohol concentration (BAC) of 0.08% or higher.
Key Legal Issue:
Is the chemical test reliable and admissible?
Possible Defenses:
- Rising blood alcohol: The driver’s BAC may have been below 0.08% while driving but rose afterward.
- Improper calibration: Breath machines require strict maintenance protocols.
- Mouth alcohol contamination: Recent drinking, belching, or dental work can skew results.
- Partition ratio variability: Breath tests estimate BAC and can be inaccurate for certain individuals.
Takeaway: Breath numbers look powerful to a jury—but they are far from infallible.
5. Blood Test Cases
Scenario:
Blood is drawn after arrest, often when drugs are suspected or after a refusal.
Key Legal Issue:
Was the blood draw constitutional and properly handled?
Possible Defenses:
- Chain of custody issues: Any break in documentation can create doubt.
- Fermentation or contamination: Improper storage can artificially increase alcohol levels.
- Illegal warrant or no warrant: Under Missouri v. McNeely, warrantless blood draws are often unconstitutional unless exigent circumstances exist.
- Lab errors: Even accredited labs make mistakes.
Takeaway: Blood tests are considered the “gold standard,” but they are still vulnerable to attack.
6. Drug DUI (DUID)
Scenario:
The driver is suspected of impairment from marijuana, prescription drugs, or other substances.
Key Legal Issue:
Can the prosecution prove actual impairment—not just presence of a substance?
Possible Defenses:
- No per se limit: Unlike alcohol, there is no universally accepted THC impairment threshold in California.
- Residual presence: Drugs can remain in the body long after impairment ends.
- Unreliable drug recognition evaluations: These rely heavily on officer interpretation.
- Prescription defense: Lawful use does not equal impairment.
Takeaway: DUID cases are often more defensible because the science is less precise.
7. Refusal Cases
Scenario:
The driver refuses a chemical test after arrest.
Key Legal Issue:
Did the driver knowingly and willfully refuse under California’s implied consent law?
Possible Defenses:
- Confusion or misunderstanding: The admonition must be clear.
- Language barriers: Miscommunication can invalidate a refusal.
- Medical inability: Some individuals physically cannot complete a breath test.
- Officer error: Failure to properly advise consequences can defeat the allegation.
Takeaway: Refusal enhances penalties, but it also creates opportunities to challenge the officer’s conduct.
8. Accident-Related DUIs
Scenario:
A DUI arrest follows a collision, sometimes involving injury.
Key Legal Issue:
Was impairment actually the cause of the accident?
Possible Defenses:
- Causation challenge: The prosecution must link impairment to the crash—not just show drinking.
- Third-party fault: Another driver, road hazard, or mechanical failure may be responsible.
- Post-accident drinking: In rare cases, alcohol consumption occurs after the incident.
Takeaway: Juries often assume guilt when there’s an accident—but causation is a powerful defense angle.
9. Under-21 DUI (Zero Tolerance)
Scenario:
Drivers under 21 are charged with having a BAC of 0.01% or higher.
Key Legal Issue:
Accuracy of the test and legality of the stop.
Possible Defenses:
- Same chemical test challenges as adult cases.
- Unlawful stop: Still the first line of defense.
- Procedural violations: These cases often rely heavily on administrative processes.
Takeaway: These cases can be beaten on technical and constitutional grounds.
10. Prior DUI Enhancements
Scenario:
A defendant faces increased penalties due to prior convictions.
Key Legal Issue:
Validity of prior convictions.
Possible Defenses:
- Invalid prior plea: Lack of proper advisements in earlier cases.
- Out-of-state priors: Not all qualify under California law.
- Timing issues: Priors must fall within the statutory lookback period.
Takeaway: Challenging priors can dramatically reduce exposure.
Strategic Themes Across All DUI Cases
No matter the scenario, strong DUI defenses usually revolve around a few core principles:
1. Attack the Stop
If the officer lacked reasonable suspicion, the case can collapse early.
2. Undermine the Investigation
From FSTs to officer observations, much of the case is subjective.
3. Challenge the Science
Breath and blood testing are technical—and technical evidence is where mistakes happen.
4. Focus on Timing
BAC at the time of driving—not testing—is what matters.
5. Humanize the Defendant
Jurors relate to explanations like fatigue, stress, or normal behavior misinterpreted as impairment.
Final Thought
DUI cases in California are rarely as straightforward as they appear in a police report. What looks like a strong case on paper often falls apart under careful legal scrutiny. The difference between a conviction and a dismissal—or a significant reduction—usually comes down to identifying the weak link early and pressing it hard.
If you approach these cases methodically—challenging the stop, the procedures, and the science—you give yourself the best chance to change the outcome. Call Irvine, Newport Beach, Santa Ana, Fullerton Westminster attorney William M. Weinberg for a confidential consultation at 949.474.8008 or at bill@williamweinberg.com