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DUI Driving Cues

California police officers must have probable cause or reasonable suspicion to make a traffic stop to investigate a possible DUI. Probable Cause is established if a law (such as a Vehicle Code violation) has been broken. Reasonable Suspicion requires the officer to suspect criminal activity (such as a person driving driving under the influence) has occurred or is occurring.

The officer may observe (or claim to observe) irregular driving patterns, such as weaving or lane straddling. Weaving within a lane may provide a law enforcement officer reasonable suspicion to stop and investigate whether criminal activity (such as driving under the influence) is the reason for the weaving. In 1985, the Appellate Department of the Superior Court, San Diego, determined that pronounced weaving within the lane of travel for about three-quarters of a mile provided the officer with reasonable suspicion to stop the vehicle to conduct an investigation for driving under the influence. (People v. Perez (1985) 175 Cal.App.3d Supp. p. 8.)

Weaving outside of the lane, lane straddling or changing lanes without signaling may provide a law enforcement with probable cause to make the traffic stop because the officer may be able to justify issuing a citation to the driver having violated California Vehicle Code section 21658. The National Highway Traffic and Safety Administration (NHTSA) has reported that there are 24 driving cues which may be used by law enforcement officers to predict that a driver's BAC is .08 percent or greater.

This list is not exhaustive, but those cues were divided into four categories:

Problems in Maintaining Proper Lane Position

  • Weaving
  • Weaving Across Lane Lines
  • Straddling a Lane Line
  • Drifting
  • Swerving
  • Almost Striking a Vehicle or Other Object
  • Turning With a Wide Radius, or Drifting During a Curve

Speed and Braking Problems

  • Stopping Problems (Too Far, Too Short, Too Jerky)
  • Accelerating for no Reason
  • Varying Speed
  • Slow Speed

Vigilance Problems

  • Driving Without Headlights at Night
  • Failure to Signal a Turn or Lane Change, or Signaling Inconsistently With Actions
  • Driving in Opposing Lanes or the Wrong Way on a One-Way Street
  • Slow Response to Traffic Signals
  • Slow or Failure to Repsond to Officer's Signals
  • Stopping in the Lane for No Apparent Reason

Judgment Problems

  • Following Too Closely
  • Improper or Unsafe Lane Change
  • Illegal or Improper Turn (too fast, jerky, sharp, etc.)
  • Driving on Other than the Designated Roadway
  • Stopping Inappropriately in Response to an Officer
  • Inappropriate or Unusual Behavior
  • Appearing to Be Impaired

After the Stop. After the officer has stopped the suspected drunk driver, the following cues help him to determine if a DUI arrest should be made:

  • Difficulty with Motor Vehicle Controls
  • Difficulty Exiting the Vehicle
  • Fumbling with Driver's License or Registration
  • Repeating Questions or Comments
  • Swaying, Unsteady, or Balance Problems
  • Leaning on the Vehicle or Other Object
  • Slurred Speech
  • Slow to Respond to Officer/Officer Must Repeat Questions
  • Provides Incorrect Information or Changes Answers
  • Odor of Alcoholic Beverage from the Driver

In addition to the list of DUI driving cues presented by the National Highway Traffic and Safety Administration (NHTSA), there are other bases for law enforcement conducting a DUI investigation. These include an accident or a report by a person reporting a driver may be under the influence. It is not uncommon for law enforcement officers to receive a report of an accident involving a hit and run or the report of a person driving under the influence and going to the address where the car is registered, knocking on the door and arresting the person who answers.

Contact The Office

Mr. Tayac and the DUI investigators and experts working with him stand ready to help you or your family member. A member of the office is available to speak with you regarding the case any day of the week between the hours of 8:00 a.m. and 8:00 p.m. Pacific Standard Time at 415-552-6000.

If you hire the Law Office of Robert Tayac, you will know that you have retained the services of the most knowledgeable and experienced DUI defense team.

Why Choose Our Firm?

Attorney Robert Tayac Puts a Long, Decorated Career to Work for You
  • Puts Over 20 Years of Experience Toward Your Case

  • Specialized Education in DUI Defense

  • Has Trained Other Attorneys in San Francisco

  • Former San Francisco Police Officer & Police Inspector

  • Certified by the SFPD on the Intoxilyzer 5000 Testing Device

  • Co-Authored the 4th Edition of California Drunk Driving Defense

  • Boasts a Successful Record Achieving the Best Result for His Clients

  • Takes the Time to Understand You & Your Case

Client Testimonials

  • “Without Mr Tayac's knowledge and drive to succeed, I most likely would not be able to write this review today.”


  • “I did have to pay a fine and attend a 3 month school but I was able to maintain my license.”


  • “...thank you for walking me through this process and making me feel at ease.”


  • “Don't go it alone - you will get a very different (better) result with Robert's lead.”


  • “I am very happy with his professional expertise that he provided during this stressful time.”


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