Under most DUI-DWI statutes, it is illegal to drive a vehicle while “under the influence” of alcohol or other intoxicants. However, the degree of physical or mental impairment required for a person to be “under the influence” varies considerably from state to state. Impairment “in any degree,” “in some degree,” and “to an appreciable extent” have each been held sufficient to render a person “under the influence.”
Other courts have held that the degree of impairment necessary for a person to be deemed “under the influence” is measured by the person’s ability to operate a vehicle safely. In such cases, the standard is whether the defendant’s consumption of alcohol diminished his or her ability or capacity to operate a vehicle safely.
Impairment of one’s ability or capacity to operate a vehicle is usually linked to an impairment of the person’s senses, judgment and motor skills, although proof of actual erratic or unsafe driving is not normally required. Thus, a person is “under the influence” when that person does not possess the clearness of intellect and control that he or she would otherwise have.
It should be noted that some courts distinguish between the terms “intoxicated” and “under the influence,” while other courts use the terms interchangeably. The courts that distinguish between the terms usually find “intoxicated” to be the stronger term and that it requires a greater degree of functional impairment. Thus, it has been held that an intoxicated person is necessarily under the influence of alcohol, but one does not have to be intoxicated to be under the influence of alcohol.
The degree of mental or physical impairment required for a person to be deemed “under the influence” or “intoxicated” varies not only from state to state, but often among the various drunk or impaired driving offenses within a state. It is obviously important to ascertain the degree of impairment required for conviction under each offense. Often the required degree of impairment is found in the pattern jury instructions approved for use in a particular state. In some states, the degree of impairment required for conviction is set forth statutorily. Otherwise, the required degree of impairment must be ascertained from the local case law. Generally speaking, your level of intoxication will initially be noted by field sobriety tests but must be legally established using more comprehensive blood alcohol content tests.