DUI Science: How To Read The Correlation Studies in the NHTSA Manual

Researchers at the National Highway Traffic Safety Administration (NHTSA) have created a booklet for law enforcement called “Guide for Detecting Drunk Drivers at Night.”  This guide sets forth some of the most common and reliable indicators of drunk driving.  The list divides driving behaviors into four areas of clues that officers are trained to look for: Maintaining Lane Position, Speed and Braking, Vigilance, and Judgment.  The following is a list of symptoms in descending order of probability that the person observed is at or above a .10% BAC, thus statutorily driving while intoxicated.

  1. Turning with a wide radius
  2. Straddling center of lane marker
  3. “Appearing to be drunk”
  4. Almost striking object or vehicle
  5. Weaving
  6. Driving on other than designated highway
  7. Swerving
  8. Speed more than 10 mph below limit
  9. Stopping without cause in traffic lane
  10. Following too closely
  11. Drifting
  12. Tires on center or lane marker
  13. Braking erratically
  14. Driving into opposing or crossing traffic
  15. Signaling inconsistent with driving actions
  16. Slow response to traffic signals
  17. Stopping inappropriately (other than in lane)
  18. Turning abruptly or illegally
  19. Accelerating or decelerating rapidly
  20. Headlights off
What’s more, they have assigned a probability of intoxication to each of the indicators.  For example, a person who turns with a wide radius will have a blood-alcohol concentration of .10 or higher 65 out of 100 times.  A person who  appears drunk will have a blood-alcohol concentration of .10 or higher 60 times out of 100.  There is also a procedure for calculating multiple factors, “When two or more cues are seen, add 5% to the highest value among the cues observed.”  If we see turning with a wide radius and a suspect who appears drunk, we take the higher number and add 10 (65 + 5 = 70).   Thus, 30 people out of 100 who appear drunk and turn with a wide radius are not at or above the .10 BAC threshold.

Another example: drifting at night had a 45% correlation to a .10 BAC or more and braking erratically  has a correlation of  35% to a BAC of .10 or more.  Thus if we have a driver who was breaking erratically (35%) and drifting (45%) we add 5% to the highest clue to conclude that the driver would have a correlation of 50% to a BAC of .10 or more (only if he or she were driving at night, of course).  Let’s throw in another clue.  Say our suspect was also turning with a wide radius which is correlated to a 60% chance the driver is above a .10 BAC.  When three or more clues are present we add 10% to the highest clue total (in this case the 60% turning with a wide radius) for a total correlation of 70%.  The individual clues have numbers written beside them in the manual which gives the correlation for the clue alone and in combination.  For instance “Problem Maintaining Proper Lane Position” has a correlation of 50% when indicated alone and a 75% correlation when combined with any other clue.  You can visit the NHTSA website at http://www.nhtsa.gov/people/injury/alcohol/dwidwihtml/index.htm for more on the studies and the driving clues or read How to Beat a DUI by James Nesci, pp. 13-15.

DUI attorney Charles M. Rowland II dedicates his practice to defending the accused drunk driver in Fairborn, Dayton, Springfield, Kettering, Vandalia, Xenia, Miamisburg, Springboro, Huber Heights, Oakwood, Beavercreek, Centerville and throughout Ohio.  He has the credentials and the experience to win your case and has made himself the Miami Valley’s choice for DUI defense.  Contact Charles Rowland by phone at 937-318-1DUI (937-318-1384), 937-879-9542, or toll-free at 1-888-ROWLAND (888-769-5263).  For after-hours help contact our 24/7 DUI HOTLINE at 937-776-2671.  For information about Dayton DUI sent directly to your mobile device, text DaytonDUI (one word) to 50500.  Follow DaytonDUI on Twitter @DaytonDUI or Get Twitter updates via SMS by texting DaytonDUI to 40404. DaytonDUI is also available on Facebook and on the DaytonDUI channel on YouTube.  You can also email Charles Rowland at: CharlesRowland@DaytonDUI.com or write to us at 2190 Gateway Dr., Fairborn, Ohio 45324. “All I do is DUI”