Articles Tagged with DWI Evidence Rules

In North Carolina impaired driving cases where retrograde extrapolation becomes relevant, chemical testing is often separated from the driving event by significant delay. This is most commonly seen in serious vehicular prosecutions where impaired driving serves as a predicate offense, including collision investigations involving injury or death, where scene management, medical transport, search warrant procedures, and hospital blood draws may delay specimen collection for three or more hours.

This timing gap can create an evidentiary question that prosecutors sometimes attempt to address using a technique known as retrograde extrapolation, a calculation intended to estimate a prior blood alcohol concentration based on a later chemical test.

Retrograde extrapolation relies not on statutory fiat but on biology. Whether it carries scientifically reliable, relevant evidentiary value in any individual case depends on the science of alcohol absorption, distribution, and elimination. Put simply, contrary to the assertions of some, it’s neither clear-cut nor fait accompli.