Police Try to Prove Marijuana Causes Driving Impairment

After a DUI arrest, police administer a breath test. (It's significant that, in Oregon, a breath test is not administered before a DUI arrest.)

If the result of the breath test is below the presumptive limit of .08 percent breath alcohol, police are trained to interpret this information to mean that the level of alcohol is "inconsistent with the level of impairment observed." Their training also has them call in another police officer, known as a "drug recognition evaluator," or DRE. (Occasionally, an officer prefers to be called a drug recognition "expert.")

These police officers are not medically trained or certified. They are police officers who have received special police training in gathering evidence in a DUI case.

A DRE will take a driver who has been arrested for DUI through a long examination referred to as a "12-Step" protocol.

If a police suspect a driver has used marijuana (which frequently happens, because drivers who have used marijuana generally admit it), the DRE will administer a series of tests. These are supposed to prove that the person who admitted to using cannabis is somehow impaired by it.

At the end of the DRE testing, the police officer asks for a urine sample, which is sent to the Oregon State Police crime lab for analysis.