Austin Police Chief Art Acevedo wants to create a new criminal offense: "driving while ability impaired." The problem with the current Texas law prohibiting "driving while intoxicated" (DWI), Acevedo explained to the Austin-American Statesman in October, is that it doesn't allow him to arrest a driver whose blood-alcohol content (BAC) is below 0.08 percent unless there's additional evidence of impairment.

"People sometimes focus on how many drinks they can have before they'll go to jail," Acevedo explains. "It varies.…A person may be intoxicated at 0.05, and you don't want them out driving." Acevedo wants to be able to arrest people with BAC levels as low as 0.05 percent, and he may have support for that idea in the state legislature. John Whitmire (D-Houston), chairman of the state Senate's Criminal Justice Committee, likes his idea.

Acevedo and Whitmire are right, though probably not in the way they intended. People do react to alcohol differently. For many people one drink may well be too many. Experienced drinkers, by contrast, can function relatively normally with a BAC at or above the legal threshold. A person's impairment may also depend on variables such as the medications he is taking and the amount of sleep he got the night before.

Acevedo's objections to the legal definition of intoxication highlight the absurdity of drawing an arbitrary, breathalyzer-based line between sobriety and criminal intoxication. But the right solution is not to push the artificial line back farther. Instead we should get rid of it entirely by repealing drunk driving laws.

Consider the 2000 federal law that pressured states to lower their BAC standards to 0.08 from 0.10. At the time, the average BAC in alcohol-related fatal accidents was 0.17. Two-thirds of such accidents involved drivers with BACs of 0.14 or higher. (The federal government classifies a fatal accident as "alcohol-related" if it involved a driver, a biker, or a pedestrian who had consumed alcohol, whether or not drinking actually contributed to the accident.) In 1995 the National Highway Traffic Safety Administration studied traffic data in 30 safety categories from the first five states to adopt the new DWI standard. In 21 of the 30 categories, those states were either no different from or less safe than the rest of the country. Once the 0.08 standard took effect nationwide in 2000, alcohol-related traffic fatalities increased, following a 20-year decline.

Critics of the 0.08 standard predicted this would happen. The problem is that most people with a BAC between 0.08 and 0.10 don't drive erratically enough to be noticed by police officers in patrol cars. So police began setting up roadblocks to catch them. But every cop manning a sobriety checkpoint aimed at catching motorists violating the new law is a cop not on the highways looking for more seriously impaired motorists. By 2004 alcohol-related fatalities went down again, but only because the decrease in states that don't use roadblocks compensated for a slight but continuing increase in the states that use them.

These constitutionally dubious checkpoints have become little more than revenue generators for local governments. When local newspapers inquire about specific roadblocks after the fact, they inevitably find lots of fines for minor infractions but few drunk drivers. In 2009, according to a story at the investigative journalism site California Watch and data from the University of California at Berkeley, 1,600 sobriety checkpoints in California generated $40 million in fines, $30 million in overtime pay for cops, 24,000 vehicle confiscations, and just 3,200 arrests for drunk driving. A typical nightly checkpoint would divert 20 or more cops from other tasks while yielding a dozen or more vehicle confiscations but only about three drunk driving arrests.

In addition to the Fourth Amendment issues raised by roadblocks, the Fifth Amendment right against self-incrimination has been turned upside down by state laws that instantly suspend the licenses of drivers who refuse to take roadside breath tests. Most manufacturers of breath test machines have refused to turn over their source code, meaning DWI defendants can't assess the machines' margin of error—a significant factor in a case where the difference between 0.80 and 0.79 for a first offense can mean $1,000 or more in fines, mandatory alcohol awareness classes, and loss of driving privileges for up to a year.

Blood tests are far more accurate, but by the time a driver is pulled over, questioned, taken to the nearest hospital, and had his blood drawn, his BAC may be significantly different from what it was when he was driving. Perversely, the time lapse can have the effect of protecting guiltier motorists. Imagine a driver pulled over or stopped at a checkpoint after having "one for the road," knowing his house is a short drive away and the last drink won't kick in until he's sitting on his couch. At the time he is stopped, he is under the legal limit. But his BAC is rising, and it tops 0.08 by the time his blood is drawn at the hospital. By contrast, a driver who is impaired when he's pulled over, but who stopped drinking an hour or so before, benefits from the delay, since his BAC is falling by the time he arrives at the hospital.

Many states have tried to solve this problem by claiming another alarming power: They now allow police to forcibly take a blood sample on the side of the road.

These ever-expanding enforcement powers miss the point: The threat posed by drunk driving comes not from drinking per se but from the impairment drinking can cause. That fact has been lost in the rush to demonize people who have even a single drink before getting behind the wheel (exemplified by the shift in the government's message from "Don't Drive Drunk" to "Don't Drink and Drive"). Several studies, such as a 2005 paper in the British Medical Journal, have found that talking on a cell phone, even with a hands-free device, causes more driver impairment than a 0.08 BAC. A 2001 American Automobile Association study found several other in-car distractions that also caused more impairment, including eating, adjusting a radio or CD player, and having kids in the backseat.

If our ultimate goals are to reduce driver impairment and maximize highway safety, we should be punishing reckless driving more consistently. It shouldn't matter if it's caused by alcohol, sleep deprivation, prescription medication, text messaging, or road rage. If lawmakers want to stick it to dangerous drivers who threaten everyone else on the road, they can dial up the civil and criminal liability for reckless driving, especially in cases that result in injury or property damage.

Doing away with the specific charge of drunk driving sounds radical at first blush, but it would put the focus back on behavior, where it belongs. The punishable act should be violating road rules or causing an accident, not the factors that led to those offenses. Singling out alcohol impairment for extra punishment isn't about making the roads safer. It's about a lingering hostility toward demon rum.

Radley Balko is a senior editor at reason.