Now that marijuana is legal for recreational use in Colorado and Washington State, authorities need some way of deciding when a person is too stoned to drive. Law enforcement has set legal limits, but are they too low? Washington TV station KIRO got a bunch of people high and set them loose on a police road course, but they actually didn't do all that bad.

So how do police figure a person is stoned or cracked out rather than drunk? Enter the Drug Recognition Experts (DREs). If someone has been drinking, the signs of impairment are usually pretty straightforward. It doesn't take a rocket scientist to pick up on slurred speech and booze fumes. But ferreting out drug impairment can be a bit more tricky, particularly because drugs come in various strengths and affect people in differnt ways.

Based upon the amount of marijuana in KIRO's test recipients' blood, they were well over the legal limit while driving the course. But both the DRE observing the test and the driving instructor in the car with them said all three of them did pretty well initially. Naturally, as they got more and more baked, they started doing all those things you've seen Cheech and Chong do in the movies: driving too slow, swinging the wheel wildly and cackling like a 10-year-old at an arcade, etc.

Photo credit: KIRO