Retrograde Extrapolation can be a Powerful DUI Defense Tool
Melanie’s Law now permits a jury to convict a person of drunk driving in Massachusetts when the person is found operating a motor vehicle with a blood alcohol percentage of .08 or higher, which is the legal limit in Massachusetts. What is relevant is the defendant’s blood alcohol level at the time he or she was driving and not, necessarily, at the time he or she took the breathalyzer test, which may have been given a long time after the DUI traffic stop.
When a defendant takes a post-arrest chemical breath or blood test, that test provides a snapshot of the blood alcohol concentration (BAC) at the time the test is administered. That is not necessarily an accurate reflection of the person’s BAC at the time of his or her arrest.
The more time that goes by between the driving and the breathalyzer, the less accurate the breath test results are. It is for this reason that as soon as a person arrested for DUI agrees to take a breathalyzer test, “he or she, as soon as reasonably possible, shall be taken to a facility with certified breath testing devices.” An undue delay may result in an acquittal.
As drinking diminishes or ceases, the BAC begins to decrease as alcohol is eliminated from the body. The body eliminates alcohol through the liver at a slow but consistent rate. Because of this rise and fall (known as the blood-alcohol curve), a person’s BAC at the time of the breathalyzer could either be higher or lower than at the time of driving.
A driver’s blood alcohol content at the time of his or her arrest can be established using a process called retrograde extrapolation. Results achieved through this process are admissible in Massachusetts DUI trials to show what a defendant’s BAC was at time of driving, prior to the breathalyzer or blood test. It can be an effective tool which Massachusetts DUI lawyers can use to achieve not guilty verdicts and dismissals of drunk driving charges.
The best Massachusetts DUI attorneys thoroughly understand how retrograde extrapolation, along with expert opinion evidence as to what a defendant’s blood-alcohol content actually was at the time of driving can save a client’s license, livelihood, and life.
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