NTSB Chairwoman Deborah Hersman (Ann Heisenfelt/AP)

Time to close your tab: The National Transportation Safety Board (NTSB) wants to reduce the amount of booze you have to drink to count as a "drunk driver."

Currently, the threshold is set at a blood alcohol content of 0.08 percent, as a result of a transportation bill signed into law by President Clinton in 2000, which stated that states had to adopt the 0.08 threshold by 2004 or else have their highway funding revoked.

But in a new report, the NTSB argues that this threshold is too high, and that it should be reduced further to 0.05. For reference, the average woman weighing 165 pounds would have to consume three beers to top 0.05, four to top 0.08, and five to top 0.10 (change that to four, five and six for the average man weighing 195 pounds).

It's unlikely that this change will happen any time soon. The NTSB first recommended lowering the threshold from 0.10 to 0.08 in 1982. Utah, which has a large Mormon teetotaling population, adopted the new standard the next year, but by the time the federal government adopted the standard in 2000, only 18 states and the District of Columbia had followed suit. Passing the federal standard took some political heavy lifting on Clinton's part, and that was after decades of lobbying from Mothers Against Drunk Driving and other groups for the new standard. So don't expect the 0.05 standard to get by too easily.

But leaving political plausibility to the side, is the 0.05 standard a good idea? There's some evidence to suggest that reducing the threshold for drunk driving can save lives:

The 0.08 switch worked

 (Tracy A. Woodward/The Washington Post)

One way to evaluate that would be to see whether the national switch to the 0.08 standard made a difference in terms of traffic deaths and injuries. There was considerable research before the bill was passed predicting that it would. Perhaps the most notable study, a 1996 paper in the American Journal of Public Health by Boston University's Ralph Hingson, Timothy Heeren and Michael Winter, compared states that had voluntarily adopted the 0.08 limit to nearby states that had not.

They found that states that had adopted the limit experienced a 16 percent decline in the share of fatal car crashes that involved a fatally injured driver whose BAC was 0.08 or above, relative to states that hadn't adopted the limit. They concluded that the lower standard would, if adopted nationally, probably prevent 500 to 600 fatal crashes a year. A 2000 study by the same authors found similar effects for states that had recently adopted the new standard, estimating that national adoption would save 400 to 500 lives a year (a lower number because more states were already on board).

A 2001 study by National Highway Traffic Safety Administration researchers investigating the 1997 implementation of the 0.08 standard in Illinois found similar results. They built a model to predict the share of fatalities where drivers had positive BACs, and compared its predictions to what actually happened in 1997, 1998 and 1999. They found that the new limit caused a sudden break with previous patterns:

They estimate that the change probably saved about 60 lives in Illinois in 1998. And these are just the tip of the iceberg. Numerous other pre-federal change studies found that states that had adopted the 0.08 standard had lower rates of alcohol involvement in crashes. Just about the only one that didn't concerned North Carolina's law, where no statistically significant effect was found.

And studies since the bill's adoption back that up. A 2005 meta-analysis analyzing 19 jurisdictions with the 0.08 limit found an average decline in the share of fatal crashes involving drinking drivers of 14.8 percent, and concluded that national adoption would have saved 947 lives in 2000. A 2007 retrospective study, looking at deaths through 2002, after the national standard law was passed, estimated that the standard saves about 360 lives a year.

Would going lower help?

If you drank all these, you definitely wouldn't be allowed to drive in Germany. (Michael Dalder/Reuters)

That last study extrapolates out to estimate that a 0.05 standard would save another 538 lives a year. We actually don't have to extrapolate from U.S. experience, though, as 0.05 is, by far, the most common international threshold. France, Germany, Australia, Italy, Spain and Israel all set their thresholds at 0.05. Some countries set them lower still. Norway and Sweden use a 0.02 threshold, while Japan uses 0.03.

In countries that reduced to 0.05, research suggests that fatalities fell. The University of Barcelona's Daniel Albalate found that European countries such as France and Germany that adopted the lower standard in the 1990s saw reductions in road fatalities relative to ones like the UK that didn't lower their standards, amounting to a 6.1 percent reduction in the fatality rate per kilometer driven. Australian researchers in 1997 found that New South Wales and Queensland, which had adopted the lower 0.05 standard, experienced substantial reductions in serious injuries and fatalities as a result. A 2000 evaluation of Austria's adoption of the lower limit found a significant decline in accidents, and a truly dramatic one (over 30 percent) for novice drivers.

All told, one literature review found eight studies on transitioning to a 0.05 threshold, all of which found positive effects.

What else could we do?

Ignition interlocks! (Tracy A. Woodward/The Washington Post)

Of course, lowering the legal limit isn't the only way to crack down on drunk driving, though the evidence suggests it would help. South Dakota, for example, has experimented with a program called the 24/7 Sobriety Project, wherein offenders were required to either wear a constant alcohol monitoring device or else go in for breathalyzer tests twice a day. A RAND evaluation found the program led to a 12 percent reduction in a repeat DUI arrests and a 9 percent reduction in domestic violence arrests.

A program called Saving Lives in Massachusetts, which involved a variety of approaches,  from setting up peer education programs in schools to awareness days to police training, was found in a quasi-experimental study to reduce alcohol-related fatal crashes by 42 percent, and all fatal crashes by 25 percent. A randomized evaluation of a program that involved counseling problem drinkers during emergency room visits also found good results.

A checkpoint system in Tennessee was found to reduce fatal accidents by 20.4 percent, and two randomized studies found that a Maryland policy requiring "ignition interlock" systems, wherein offenders with alcohol-related traffic violations have to pass a breathalyzer test before their cars will start, reduced recidivism considerably. One study found a 64 percent reduction in new traffic violations in the first year as a result of the interlock, and another found a 36 percent reduction when the interlock is in effect, and a 26 percent reduction for the two years afterward. Non-randomized studies have also found ignition interlocks significantly reduce re-offense.

Almost all of those programs had more significant effects than reducing the threshold was found to in the studies reviewed above. That suggests that even if reducing the threshold helped, other, less controversial policies could do the trick with less political resistance.