Hugh Pickens writes writes: "AP reports that with Pot soon legal under state laws in Washington and Colorado, officials in both states are trying to figure out how to keep stoned drivers off the road as law enforcement officials wonder about whether the ability to buy or possess marijuana legally will bring about an increase of marijuana users on the roads. "We've had decades of studies and experience with alcohol," says Washington State Patrol spokesman Dan Coon. "Marijuana is new, so it's going to take some time to figure out how the courts and prosecutors are going to handle it. But the key is impairment: We will arrest drivers who drive impaired, whether it be drugs or alcohol." Marijuana can cause dizziness and slowed reaction time, and drivers are more likely to drift and swerve while they're high and Marijuana legalization activists agree people shouldn't smoke and drive. But setting a standard comparable to blood-alcohol limits has sparked intense disagreement because unlike portable breath tests for alcohol, there's no easily available way to determine whether someone is impaired from recent pot use. If scientists can't tell someone how much marijuana it will take for him or her to test over the threshold, how is the average pot user supposed to know? "A lot of effort has gone into the study of drugged driving and marijuana, because that is the most prevalent drug, but we are not nearly to the point where we are with alcohol," says Jeffrey P. Michael, the National Highway Traffic Safety Administration's impaired-driving director. "We don't know what level of marijuana impairs a driver.""