Here in Massachusetts a defendant can be convicted of operating under the influence of alcohol (OUI) if he drives a vehicle on a public way while impaired.
Impairment can be shown with circumstantial evidence and/or breath test results of .08% blood alcohol content (BAC).
A breath test result of .o8% or higher–without more–is sufficient for a jury to conclude that an OUI defendant was impairment.
(Of course, the defendant may still challenge the validity of the breath test result at trial. For more, see my earlier post Challenging Breathalyzer Results in Massachusetts.)
But what happens when a defendant’s BAC is less than .08?
If the BAC is between .06% and .07% the prosecution is not entitled to an inference that the OUI defendant was impaired.
The .06-.07 result can be introduced to show that the defendant consumed alcohol.
But “impairment” must be established with circumstantial evidence (e.g., admissions, open containers, police observations, etc.)
See Model Jury Instruction 5.310(5) and G.L. c. 90, Section 24(1)(e).
If the defendant’s BAC is .05 or lower, there is a statutory inference that the defendant was not impaired at the time of the test. See Model Jury Instruction 5.310(4).
Usually prosecutors will not go to trial when the BAC is less than .08%.
However, if the defendant is allegedly impaired due to a combination of drugs and alcohol, the prosecutor may likely press forward despite to the low breath test reading.