There is a bit of media buzz about a new study on drinking and driving authored by researchers at UCSD (Phillips & Brewer, 2011). In short, the researchers analyzed the Fatality Analysis Reporting System (FARS) data to find a relationship between BAC and vehicle crash injury and death. What was unique about their study was that instead of analyzing BAC categories (typically 0.0, .01-.09, .10+), the researchers left the BACs in units of .01. That meant that they could look for crash-risk increases even at very low levels… even .01 BAC.

And what did they find? Well, in fact risk goes up at levels as low as .01. Perhaps this should not be surprising because laboratory studies have long found measurable impairments at any BAC above zero. However some have argued that low-level effects were minimal enough that with proper motivation, these minimal impairments could be overcome. It is certainly the case that standard field sobriety tests are very poor at detecting impairments at such low levels (McKnight, Langston, McKnight, & Lange, 2002).

So at the population level increased crash and injury risk from low levels can be detected. The authors note that there is also a relationship between these low levels of alcohol and speeding and failure to wear seatbelts. These factors along with BAC were associated with more severe crashes.

There are always questions raised by research, especially correlational studies such as this one. For instance, we cannot be sure that certain risk-taking personality traits may account for all the relationships observed: speeding, BAC elevation, seatbelt non-use, and crashes. Thus, there may be no causal connection between low BAC levels and risk. Further the authors did not control for other drugs that may be more prevalent within those with positive BACs.

While the authors called for lowering the per se alcohol limit from the current .08, given current DUI enforcement practices, it is unlikely that enforcement would adequately detect the subtle impairments that are manifest by BACs much lower than .05.

So this means a driver should not drink at all. Our education programs should emphasize complete abstinence from alcohol for those planning on driving. We can always quibble about policy, enforcement and personal freedom. But the lab studies and epidemiological data converge to show impairments at BACs much lower than the current .08 BAC legal limit. Also, we must remember to consider the growing research on drivers who are mixing drugs and alcohol; their risk may be especially elevated even when alcohol levels are low.

References

McKnight, A. J., Langston, E. A., McKnight, A. S., & Lange, J. E. (2002). Sobriety tests for low blood alcohol concentrations. Accident; Analysis and Prevention, 34(3), 305-311.

Phillips, D. P., & Brewer, K. M. (2011). The relationship between serious injury and blood alcohol concentration (BAC) in fatal motor vehicle accidents: BAC = 0.01% is associated with significantly more dangerous accidents than BAC = 0.00%. Addiction, no. doi:10.1111/j.1360-0443.2011.03472.x