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University of North Carolina
"2 out of 3 .00 BAC"

Project Description

The University of North Carolina at Chapel Hill (UNC) is a public, four-year university with a total student enrollment of 24,180 (15,400 undergraduate and 8,780 graduate and professional students).

In the fall of 1997 and 1999, teams from the North Carolina Highway Safety Research Center collected breathalyzer data from University of North Carolina students who were returning home to fraternities, sororities, residence halls and apartment complexes. Data were collected between the hours of 10 p.m. and 3 a.m. on every night of the week for 6 weeks. Two-thirds of the interviews took place on Thursday, Friday and Saturday. A total of 4,381 students participated in the two studies: 1,846 in 1997, and 2,535 in 1999.

Project Funding Sources

Funding for this project has been provided by:

  • The National Highway Traffic Safety Administration
  • The North Carolina Governor's Highway Safety Program
  • The U.S. Department of Education
  • The University of North Carolina's Division of Student Affairs

Project Objective

To develop a more complete understanding of student alcohol use on the UNC campus in preparation for a program to reduce excessive or dangerous drinking.

Baseline Data

Interview Procedure

Data were collected on 20 nights between October 2, 1997 and November 14, 1997, between 10 p.m. and 3 a.m. on all nights of the week. Randomly selected groups of individuals were approached by a single member of a four person interview team and asked if they would participate. Once consent was obtained, all members of two- and three-person groups were interviewed. For larger groups, three individuals were randomly selected for interview. The interview took approximately 4 minutes and requested information about activities during the night, drinking (where, when, what, how much), perceptions about alcohol use among students, mode of transportation and ways used to avoid drinking and driving. Drinkers were asked whether they felt any effects and to estimate their blood alcohol concentration (BAC)


The sampling procedure was designed to obtain a representative sample of students at a large public university who were returning home in the evening. The campus was divided into five geographically distinct routes along which interview teams walked. These routes passed every dormitory, fraternity, sorority and private dormitory on or near campus. The sampling plan was developed such that every residential location was visited at least six times: once before and after midnight on week nights (Sunday through Wednesday), Thursdays and weekends (Friday and Saturday). On each night that data were collected, three interview teams worked, covering separate routes. Respondents were sampled in the vicinity of student residences. To avoid attracting too much attention, interview team moved continuously between residences, typically collecting data at a single location for no more than 10 minutes.

Approximately half the undergraduate student body lives on campus. In order to obtain information about those who live in private residences interviews were also conducted at five large apartment complexes that, according to university records, house a large concentration of university students. At these locations, the interview procedure resembled that typically used in roadside surveys (Foss, Beirness & Sprattler, 1993). Individuals were interviewed at entrances to the apartment complex while they remained in their vehicles. An initial screening was used to avoid interviewing non-students.


Of the 2,530 persons contacted, 2,186 (86.4%) cooperated, and 2,023 (80%) completed the interview and provided a breath measurement; 109 (4.3%) declined the interview, but did provide a breath sample, and 54 (2.1%) did the interview but would not provide a breath sample.

Although persons sampled on campus were interviewed regardless of their student status, results presented here represent only those 1,846 individuals explicitly identified as students enrolled at UNC. A breath alcohol measurement was obtained for 1,790 (96.9%) of these individuals. Data presented here are not weighted to account for differential probability of selection. Accordingly, estimates of overall use for the campus must be considered tentative. Subgroup comparisons are likely to be less sensitive to varying likelihood of selection. The table below shows the full BAC distribution for the three times of the week studied.

Blood Alcohol Concentration by Time of Week
BAC mg/dL*
Week night
Thursday night
Weekend night
Total n

* Results are reported here in mg/dL, which is the preferred measure in international forums. A BAC measure of 20-49 mg/dL is equivalent to our BAC measure of .02-.049; a BAC measure of 50-79 mg/dL is equivalent to our BAC measure .05-.079, and so on.

Follow-up Study

A follow-up study was conducted in 1999 (n = 2,535). A comparison of survey results obtained in 1997 with those obtained in 1999 revealed:

  • A 9% increase in the number of students who returned home with a .00 BAC on Thursday, Friday and Saturday. (65% of students were found to have .00 BAC in 1997, while 71% had a .00 BAC in 1999: a six percentage point increase, equaling a 9% increase overall.)
  • A 30% decline in the percentage of students who returned home with a high BAC (over .08%). (13% of students were found to have a high BAC in 1997, whereas only 9% did in 1999: a four percentage point drop equaling a 30% decline overall.)

Note: The "2 out of 3 .00 BAC" campaign had only begun about one month before the follow-up survey conducted in 1999. Therefore, the reductions noted above cannot clearly be attributed to the social norms campaign only recently underway.

The combined data (years 1997 and 1999, n = 3,953) indicate that 49% of respondents would be classified as "binge drinkers," where that is defined as those (both men and women) who self-report the consumption of 5 or more drinks at an occasion at least once within the last two weeks. Interestingly:

  • Although they reported consuming 5 or more drinks on an occasion at least once during the last two weeks, nearly 50% of these so-called "binge drinkers" had zero BACs on the night they were interviewed.

Furthermore, for those who self-reported "bingeing" (defined here as the consumption of 5 or more drinks for men/4 or more drinks for women) on the night of the interview:

Another BAC study will be conducted in the fall of 2002.

Marketing Methods Employed and Primary Normative Messages
Note: The "2 out of 3 .00 BAC" social norms campaign was begun in 1999.

Primary Normative Messages

Marketing Methods Employed

Posters and zipper pulls with the message "2 out of 3 .00 BAC." In addition, numerous cash incentives are offered as a way to encourage students to know and retain the normative message, and to spread the word about it. For example, every week the "prize team" randomly selects student residence hall rooms, awarding $50 to those students with a poster hanging somewhere inside their room. In addition, every campus resident received a zipper pull with the normative message on it at the beginning of the fall 2001 semester. Ever week the "prize team" randomly stops students on campus and awards $5 to those who display this pull on something they are carrying. (The award is doubled if a pair of zipper pulls is worn as matching earrings!)

Project Co-Directors

Robert D. Foss, Ph.D.
University of North Carolina Highway Safety Research Center
CB# 3430, Chapel Hill, NC 27599
Tel 919/962-8702
Fax 919-962-8710

Sara Latta
University of North Carolina Highway Safety Research Center
CB# 3430, Chapel Hill, NC 27599
Tel 919/962-7419
Fax 919-962-8710

Further Information

"Development and Evaluation of a Comprehensive Program to Reduce Drinking and Impaired Driving Among College Students: Final Report."
Written by Robert Foss, L. Marchetti, and K. Holladay, the full text of the final report of this project published in October 2000 by the National Highway Traffic Safety Administration provides extensive information about the the BAC/social norms study conducted at UNC.

UNC's 2 Out of 3 .00 BAC Campaign
The web site of the UNC 2 out of 3 .00 BAC campaign. Contents of this site include:

  • Details of the 1997 and 1999 breathalyzer study conducted at UNC
  • Online Social Norms Trivia Contest with cash giveaway incentive
  • Social Norms Poster with cash giveaway incentive

See also:
"BACs of University Students Returning Home at Night." by R.D. Foss, K.S. Holladay, C.L. Bartley, and L.M. Marchetti. A paper presented at the proceedings of the 15th International Conference on Alcohol, Drugs, and Traffic Safety. Borlänge, Sweden: Swedish National Road Administration, 2000.
This paper reports the methods and results of the initial, 1997 breathalyzer study conducted at the University of North Carolina. Of particular interest are the data for actual student BACs by time of week and the BACs of students by mode of arrival back home.¹

See also:
Foss, R. et al. Social norms program reduces measured and self-reported drinking at UNC-CH [University of North Carolina-Chapel Hill]. The Report on Social Norms: Working Paper #14. Little Falls, NJ, PaperClip Communications, 2004.

Research: Blood Alcohol Concentration (BAC) and Breathalyzer Studies
Additional information regarding BAC and breathalyzer studies is available in this section of our web site devoted specifically to research in this area.

¹Note: Much of the text of this project description was drawn from this paper, with additional information kindly provided by Dr. Robert Foss.

**Portions of the information presented on this page were originally prepared by Michael Haines and Richard Rice and are printed here with their permission.