The Mellanby Effect: Why Impaired Individuals Should Not Be Allowed to Be Behind the Wheel.

AuthorNorman, Miriam

IN AN IMPAIRED DRIVING CASE, a prosecutor typically must prove a defendant was operating or driving a motor vehicle while impaired. Alternative to showing the defendant was driving, a prosecutor must prove he or she was in physical control of the vehicle. The usual facts of a "physical control" case include the police finding an individual "asleep" in the driver's seat of a non-running car, either on the side of the road or in a parking lot. This type of case can present challenges for the prosecutor because jurors may agree with the defendant's argument that he or she was being responsible by not driving and, therefore, find him or her not guilty. The Mellanby Effect explains why an impaired individual in physical control of a vehicle cannot be left to stay in the vehicle to just "sleep it off," and the danger posed by such a situation. It is well known that alcohol impairs judgment and the ability of thought process; alcohol is a Central Nervous System Depressant.' "Alcohol in small doses may cause performance of driving-related skills to fall off; in moderation to high amounts, alcohol diminishes performance across the board with general impairment of nervous function." (2) Several studies observed a marked decrease in the ability to divide one's attention safely, ability to track, ability to react, ability to maintain lane position, ability to appropriately apply the brakes, and ability to control the steering of the vehicle. (3) Alcohol's ability to impair higher level cognitive processing, coupled with the Mellanby Effect, is exactly why it is dangerous to allow an impaired individual to be left behind the wheel: he or she will feel better, still be above the per se level, still be appreciably affected, and yet may still choose to drive.

The Mellanby Effect is a scientific principle first discovered by Sir Edward Mellanby in 1919. (4) Mellanby found that perceived behavioral impairment at a specific blood alcohol concentration was greater when the blood alcohol concentration (BAC) was rising than when it was falling. (5) "Subjects feel less drunk during the descending limb of the BAC-time curve than at the same concentration of alcohol on the ascending limb. However, objective measures of impairment... were generally worse during the descending limb for the same BAC." (6) In easier to understand terms, the Mellanby Effect can be likened to the "highway effect."

For example, imagine an individual who drives on a feeder road to the...

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