This story is a couple weeks old but in case you missed it: An Arizona appeals court has ruled that motorists don't actually have to be under the influence to be prosecuted for driving under the influence.

Via the Associated Press:

An appeals court has issued a ruling that upholds the right of authorities to prosecute pot smokers in Arizona for driving under the influence even when there is no evidence that they are actually high. …The ruling overturns a decision by a lower court judge who said it didn't make sense to prosecute a person with no evidence they're under the influence. …The case stems from a 2010 traffic stop in Maricopa County. The motorist's blood test revealed only a chemical compound that is found in the blood after another compound produced from ingesting marijuana breaks down. According to testimony by a prosecution criminalist, the compound found in the man's blood doesn't impair the ability to drive but can remain detectable for four weeks. …However, the Court of Appeals sided with prosecutors who appealed, saying that allowing the testing for marijuana's active compound would unduly restrict law enforcement.

The ruling does not apply to the state's 35,000 medical marijuana patients, who are permitted to drive with pot in their systems if they can pass a (flawed) test for impairment. Of course, as Reason senior editor Jacob Sullum notes, early reports indicate pot may not actually impair drivers all that much.

The case will be appealed to the Arizona Supreme Court.