Necessity in a DUI-DWI case is where you admittedly drove while impaired, but that you had a good (emergency) reason for doing so.
An example is if you were at home drinking, with no intention to drive, when your wife cut her arm very badly. Ten minutes after your “911” call for emergency help, an ambulance has still not arrived at the scene to help save your wife from bleeding to death. Rather than let your wife die, you drive her to the hospital, despite knowing that you have had too much to drink before driving. You acted upon this serious emergency and drove while intoxicated since you had “no other choice” if you wanted to save her. Whether or not society would consider this justified is a question for the jury to decide.
To raise this “affirmative defense,” most states require that you notify the State that this will be part of your case. Some states require that the defense admit being impaired to be allowed to assert this “affirmative defense” or another type of affirmative defense. That way, the burden of proof typically shifts to the State to DISPROVE your assertion that “necessity” excuses you from being legally responsible for DUI-DWI.
Does DUI Necessity Defense Work?
Raising such a defense may put the State to a nearly impossible task of disproving the “affirmative defense.” You may get a reduction in charges offered, to avoid trial on the more serious charge of DUI-DWI. One possible “negotiated” reduction of the DUI-DWI charge might be reckless driving where no loss of driving privileges is involved. Furthermore, even if you lose this trial, the judge’s punishment will typically be less severe than in a normal case, due to your honest perception that you needed to act to address whatever the “necessity” was that prompted you to drive.
In other states (e.g., California), raising an affirmative defense merely shifts the burden of proof to the defendant to PROVE that defense. Therefore, due to the rule in that state putting the burden of proof on the defense, no pre-trial notice is required to be given to the prosecution.