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Scientific studies correlate traffic accidents with alcohol use

Studies statistically correlate traffic accidents/fatalities or events with alcohol use. For example, a 1978 Department of Transportation (DOT) report reviewed four U.S. studies dating back to 1938 and concluded that 9-13% of drivers in injury crashes and about 5% of drivers in property damage crashes had a blood alcohol concentration (BAC) of greater than .10%.

Also, about 30% of the fatal crashes involved at least one driver or non-occupant (i.e., pedestrian etc.) with a blood alcohol concentration (BAC) of 0.10% or greater.

Statistics do not prove that alcohol caused the traffic accidents

The statistics that correlate traffic accidents with alcohol use do not prove that alcohol caused the crashes in which drinking was involved. As the Department of Transportation (DOT) has noted: “Traffic accidents are probabilistic, with many factors entering into the probability equation. The most that can be said on the basis of epidemiologic evidence is that, on the average, alcohol beyond a certain amount, is associated with increased crash risk.”

Correlation of driving behaviors with alcohol level

Accurately determining alcohol level based on driving behavior may be difficult. One study associating blood alcohol concentration with some behaviors typically associated with driving impairment provided the following results:

Driving Behavior Average Blood Alcohol Concentration (BAC) Percentage
Equipment Violation 0.015% 10.2
Speed (high or low) 0.036% 28.6
Running Stop Sign/Failure to Yield etc. 0.038% 32.7
Drifting/Weaving 0.035% 20.4
Failure to Maintain a Single Lane 0.040% 8.2

Another study provides a list of driving behaviors and their related probability of discriminating “nighttime drunk drivers” with sober drivers. The probability statistic for each cue refers to drivers with a blood alcohol concentration (BAC) of 0.10% or greater.

Cue Probability
Turning with a wide radius: the distance between the turning vehicle and the center of the turn is greater than normal. 65
Straddling center or lane marker: vehicle is moving straight ahead with the center or lane marker between the left and right wheels. 65
Appearing to be drunk: eye fixation, tightly griping wheel, slouching in seat, erratic or obscene gestures, face close to windshield, drinking in the vehicle, driver’s head protruding from the vehicle. 60
Almost striking object or vehicle: passing abnormally close to an object or vehicle, causing another vehicle to maneuver to avoid collision. 60
Weaving: moving from one side of the roadway to the other in a zig-zag course. 60
Driving on other than designated roadway: driving at the edge of roadway, on the shoulder, off the roadway, straight through turn-only lanes. 55
Swerving: an abrupt turn from a straight course. 55
Speed slower than 10 m.p.h. below limit 50
Stopping without cause in traffic lane; stopping without observable justification. 50
Following too closely; flowing another car without maintaining minimum legal separation. 50
Drifting: driving in a straight line but at an angle to the roadway. 50
Tires on center or lane marker; the left hand set of tires is “consistently” on the center line, or either set is “consistently” on the lane marker. 45
Braking Erratically; braking in an uneven/jerky manner, unnecessarily maintaining pressure on the brake peddle “riding the brakes.” 45
Driving into opposing or crossing traffic: driving into opposing lane, backing into traffic, failing to yield the right of way, driving the wrong way on a one-way street. 45
Signaling inconsistent with actions: such as failing to signal a lane change, signaling opposite to the action, driving with hazard flashers etc. 40
Slow response to traffic signals: a longer than normal driver response to a change in the traffic signal. 40
Stopping inappropriately: vehicle stops at an inappropriate location or under inappropriate conditions other than in the traffic lane (flashing yellow light, green light, in a crosswalk etc.). 35
Turning abruptly or illegally: turning with excessive speed, turning sharply from the wrong lane, illegal U-turn, turning outside a designated turn lane. 35
Accelerating or decelerating rapidly: abrupt stop, breaking traction, acceleration or deceleration more rapid than required by traffic conditions. 30
Headlights off: driving with the headlights off at a time of day when headlights are required. 30

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Trial Strategy
Client Testimony
Cross-Examination of the Arresting Officer on Field Sobriety Tests
Closing Arguments
Frequently Asked Questions