Perceived Impairment vs B.A.C. in DWI in North Carolina

Silva, Kiernan & Associates, Pllc

“I blew a .12 but I felt fine to drive.” Or, “I drank two glasses of wine and I felt really drunk.” Both statements are examples of the difference between Blood Alcohol Concentration (B.A.C.) and perceived impairment.

When discussing DWI it is important to understand the different ways the state can prove impairment in a Driving While Impaired (DWI) case. The two standards are B.A.C or “appreciable impairment.”

The legislature has determined that a B.A.C. of .08 on a breath alcohol test is legal proof of impairment. However, the state can also prove impairment by showing the driver’s faculties were “appreciably impaired” by an intoxicating substance. The substance can be alcohol, illegal and legal drugs, inhalants, etc. A driver can also be convicted of DWI when their BAC is lower than .08.

Many people are shocked to hear they could be convicted with DWI when they blow under the legal limit. They assume that the number is the only way to convict them, and they are wrong. Perceived impairment can be described as how drunk you feel. Those who drink regularly develop a tolerance for higher levels of alcohol and feel less drunk than the occasional drinker with the same amount of alcohol.

A high tolerance results in the ability to function with a higher B.A.C. For example, a man and a woman go to dinner and each have the same amount to drink. The man will have a lower B.A.C. on average due to physical sex differences. However, if the woman drinks regularly and the man does not, the woman will have a lower level of perceived impairment. This lower level of perceived impairment will tend to result in better performance on the Field Sobriety Tests (FST).

FST’s are called divided attention tests at they require the taker to listen to complicated instructions and then perform physical tests. The higher the impairment the harder the test. So the lower tolerance drinker is risking being convicted of DWI due to inability to properly complete the tests. The driver may do terribly on the tests, and then blow under .08.

The FST performance may be enough to convict the low tolerance driver of DWI. The only good news in this situation is that a good defense attorney could make a defense from these facts. Remember, drinking and driving is not illegal, DWI is.