Drinking Drivers in North Carolina

Although crash data give an indication of the extent to which drinking drivers crash, they are a poor measure of the amount of driving after drinking. DWI arrrest data are an even poorer indicator of the extent of drinking driving; they reflect the amount of time that law enforcement devotes to this issue rather than the underlying phenomenon itself. Self-report surveys can provide some indication of the amount of drinking driving, because they cover a representative sample of the driving population. However, self-reports of drinking are subject to many errors as well as to deliberate distortions. By far the best way to measure the nature and extent of drinking driving is to conduct interviews with drivers sampled from the roads and to measure their alcohol levels directly. That approach, generally referred to a “roadside survey,” has been used by researchers in the U.S., Canada, several European countries and Australia to carefully study drinking drivers and to evaluate programs designed to discourage driving after drinking. HSRC research scientists have been extensively involved in developing, refining and using this research technique for two decades. This has involved studies in Minnesota, North Carolina, Ohio, South Carolina, Vermont and the Canadian provinces of Alberta, British Columbia and Ontario.

The 1994 - 1995 North Carolina Roadside Survey of Nighttime Drivers

From September 1994 to February 1995 (excluding December), interview teams from the University of North Carolina Highway Safety Research Center conducted interviews with drivers passing through sobriety checkpoints in 15 North Carolina counties. In addition, drivers were asked to provide a breath sample that was used to determine their Blood Alcohol Concentration (BAC). Combining this information with BAC information on drivers arrested at the checkpoints, it was possible to estimate the proportion of drivers throughout the state who drive while legally intoxicated.

Noteworthy findings

  • On a typical night, about 11 percent of drivers passing through checkpoints had some alcohol in their system, and 2.4 percent had an illegal BAC (> 0.08%). These indicate that drinking-driving was lower in North Carolina than in the U.S. as a whole.
  • Male drivers (2.5 percent) were just over four times as likely as females (0.6 percent) to have an illegal BAC.
  • Most impaired drivers had been drinking beer; 80 percent of drivers whose BAC was 0.05% or higher had been drinking beer rather than distilled alcohol (“mixed drinks”) or wine.
  • About 3.7 percent had BACs above 0.05%. Many individuals with BACs this high may be somewhat impaired. Individuals with BACs this high can be arrested for impaired driving if they appear, based on their behavior, to be impaired.
  • Impaired driving is more common after midnight. Between the hours of midnight and 3 A.M., about 4.6 percent of drivers had BACs above the legal limit, compared with 1.5 percent between 10 P.M. and midnight.
  • The proportion of drivers with illegal BACs was similar on weeknights and weekend nights.

Enforcement difficulties

Contrary to popular belief, it is quite difficult to know whether a person has been drinking based on his or her behavior. Until individuals reach a very high BAC (e.g., 0.1%2 – 0.15% or higher) the signs typically associated with alcohol impairment are not readily observable. The dangers in driving result from cognitive impairment – which cannot easily be observed – rather than impairment of gross motor skills or vision, which are normally affected only at high BACs. In addition, drinkers are not generally able to recognize their own cognitive impairment, making it difficult for them to know when they have had “too much” to drive safely.

Because alcohol is difficult to detect in individuals who are not seriously impaired, enforcing the BAC limit of 0.08% is extremely difficult. Unless a person is seriously impaired, officers often have no obvious behavioral cues that an individual has been drinking. This difficulty is reflected in the fact that among those drivers with an illegal BAC who were stopped at an enforcement checkpoint during the NC roadside survey, 59 percent were not identified as drinkers and detained or arrested.

View Full Article:

Wells JK, Greene MA, Foss RD, Ferguson SA, Williams AF. Drinking drivers missed at sobriety checkpoints. Journal of Studies on Alcohol. 1997 Sep; 58(5):513-7.

DWI system problems

There are numerous other serioius obstacles involved in effectively enforcing DWI laws and, more generally, in reducing alcohol-impaired driving in North Carolina. In 2005, the North Carolina Governor’s Task Force on Driving While Impaired, which included a representative from HSRC, released a comprehensive set of recommendations to address the many weaknesses, loopholes and inconsistencies in the North Carolina system to address impaired driving.