Effective prosecution for "drunken driving" requires a definition of impairment acceptable in all jurisdictions. This is particularly important today because, even by conservative estimates, ethyl alcohol plays a role in at least half of all fatal automobile accidents (eg, Ross, HL: Deterring the Drinking Driver, Lexington, Mass, Lexington Books, 1984; and Henry [ed]: Todd, Sanford, Davidsohn Clinical Diagnosis and Management by Laboratory Methods, ed 17, Philadelphia, WB Saunders Co, 1984, p 368).
The need for an objective, enforceable, and well-defined test for ethanol concentration in a body fluid therefore seems straightforward enough. But as the countless books, pamphlets, and policy documents on defending or deterring the "drunken driver" suggest, there is a tremendous amount of confusion—among those outside the field—about what is the best test to measure blood alcohol concentrations and even about the units in which to report these concentrations.
To convict a driver of "driving under the influence," prosecutors must show that the driver's behavior has