One local government in southwest Ireland voted in January to allow certain people living in isolated areas to drive after a few drinks. The measure was proposed by local politician Danny Healy-Rae, who argued that older rural residents were not likely to cause traffic accidents on little-used country roads, and that getting out to the pub could help prevent mental illness, according to the Guardian. Healy-Rae also owns a pub in the county, incidentally.

Whether or not you think the suggestion that drunk driving is sometimes okay is ridiculous, never mind dangerous, the story does provoke the question: How does the government decide just how many drinks is too much to drive?

In most countries with laws concerning drunk driving, the standard is set by a person’s blood alcohol content (also called blood alcohol concentration). This corresponds to the percentage of alcohol in a person’s blood. Numerous headlines have been claiming that County Kerry "legalized drunk driving," when in fact, the legal limit proposed is lower than the BAC standard in the U.S. The Kerry proposal would allow certain residents to apply for permits that allow them to drive on rural roads with a BAC of up to .07, as opposed to Ireland's current standard of .05, according to the car news site LeftLane. As of July 2004, all 50 U.S. states and the District of Columbia have criminalized driving with a BAC above .08 percent (the last holdout was Delaware). 

Blood alcohol level is obviously tied to how many drinks a person has, but is also influenced by individual traits – women process alcohol differently from men, so each drink is more likely to make a lady stumble. There are other factors that come into play, too, like weight and ethnicity. (For example, some people of Asian descent are missing an enzyme that allows them to properly digest alchohol, and therefore have a lower tolerance.)

For decades, many U.S. states set the legal BAC limit for driving somewhere between .10 and .15, but that changed starting in the late 1970s, thanks to pressure from groups like Mothers Against Drunk Driving and scientific studies showing that drinking causes loss of certain critical functions related to driving, even before someone is visibly intoxicated. At .08 BAC, the average person likely isn't falling down drunk, but probably has slightly impaired vision, hearing and reaction time, among other things.

“The risk of being in a crash gradually increases at each BAC level, but rises very rapidly after a driver reaches or exceeds .08 BAC compared to drivers with no alcohol in their blood systems,” National Highway Traffic Safety Administration researchers Delmas Johnson and James Fell wrote in a 1995 report.

Johnson and Fell examined the data on alcohol-related car crashes in five U.S. states before and after .08 BAC legislation was enacted. Their analysis showed that lowering the BAC limit to .08 generally reduced driver involvement in alcohol-related fatal crashes, ranging from a 4 percent dip in California to a 40 percent drop in Vermont.    

Plus, to reach a BAC of .08, an average 170-pound male would have to down more than four drinks within one hour on an empty stomach, while an average 137-pound female would need to take in at least three drinks in an hour on an empty stomach, according to the pair. If that number of drinks seems smaller or larger than you expected, remember that standard drink sizes may be smaller or larger than what you're served at the bar: for beer, it's 12 fluid ounces; for wine, it's five ounces; for hard liquor, it's 1.5 ounces.

“A .08 BAC is not reached with a couple of beers after work or a glass or two of wine with dinner,” Johnson and Fell wrote.

To get drunker than the old .05 BAC standard in Kerry, the average Irish farmer would probably have to tuck away more than a couple pints of Guinness. According to one online BAC calculator, an average 180-pound man could put away two pints of Guinness (about 4.2 percent alcohol by volume) within an hour and rack up a BAC of just .038, well under the old standard. Under the new standard, he can drink three pints in an hour and be legally safe to drive.

But there is a slight wrinkle to the Kerry bill: It might not actually have any force, according to the Christian Science Monitor.

"As a county council motion, the proposal has no legal status," Dublin-based Monitor correspondent Jason Walsh wrote.