Drinking and Driving: the Real Limits

Most states define a blood-alcohol concentration of 0.10% as intoxicated, but that standard is under attack from some who say that legal driving is not necessarily good driving.

California, Oregon, Utah, Maine and Vermont already have reduced their legal limits to 0.08%; put another way, that’s a concentration of eight parts per 10,000. Groups such as Mothers Against Drunk Driving are urging that other states follow suit.

The mothers’ organization would like to make the legal standard 0.0% for drivers under age 21.

The activists cite studies showing that driving can be impaired after just one drink. That amount raises alcohol concentration in the blood to about 0.02% in a 150-pound person.

With two or more drinks, judgment and the ability to gauge distances start diminishing, just as an alcohol-induced feeling of confidence kicks in.

Most states already observe 0.04% as the legal limit for drivers of buses, trucks and other commercial vehicles.

Nationwide, accident records show that by the time a driver’s alcohol level is 0.06%, he is twice as likely as a sober driver to cause a collision. A 100-pound person can reach this level with two drinks; a 160-pound person with about three drinks; a 200-pound person with about four drinks.

Drivers with a reading of 0.08% are four times as likely to crash as sober drivers. A 100-pound person can reach this level with three drinks; a 160-pound person with four or five drinks; and a 200-pound person with six drinks.

Only time--not coffee or anything else--can reduce the amount of alcohol in the blood.

Once drinking stops, the alcohol level drops at the rate of about 0.015% an hour. For example, someone with a reading of 0.13% needs about two hours to reach 0.10%, and about five hours to reach 0.05%.