When marijuana was legalized in Colorado in January, it was predicted by a number of authorities that stoned driving would become a rampant problem throughout the state. After 6 months of legalization, that prediction has not come to fruition. DUI arrests related to marijuana have increased slightly in Colorado, but alcohol is still the principal cause of a DUI arrest by far. One of the reasons for this is that marijuana consumption is harder to detect than alcohol consumption.

It is generally harder for police officers to determine if a person is under the influence of marijuana than alcohol because the indicators that a person is high are less obvious than a person who is drunk. While a blood test can eventually confirm whether a person is high or not, a police officer needs probable cause to arrest the person before a blood test can be administered, and therein lays the problem. A drunk is easy to spot. Indicators like slurred speech, bloodshot eyes, odor of alcohol, unsteady balance and bad driving are well-documented signs of impairment. Also, since the late 1970’s, law enforcement agencies throughout the country utilize standard field sobriety tests (SFST’s) that are sanctioned by the National Highway Traffic Safety Administration. These roadside tests are a routine investigative tool used by the police to detect alcohol impairment.

These SFST’s were NOT designed, however, to detect marijuana impairment. For example, one of the three standard SFST’s is called the horizontal gaze nystagmus test (HGN). Police officers observe the subject’s eyes to determine whether they jerk involuntarily, which can be an indicator of alcohol consumption. This test is not useful at all for detection of marijuana. In fact, there aren’t any specific roadside tests that specifically detect only marijuana usage.

Police agencies are working on this issue. They provide training to many of their officers to become qualified as Drug Recognition Experts (DRE’s). These officers are trained to determine whether a person is under the influence of a drug, and to determine what the drug is based upon existing field sobriety tests and other observations. While agencies are getting more DRE’s out into the field however, the majority of patrol and traffic officers who conduct traffic stops are not trained in these techniques. Also, the signs of a stoned driver are generally more subtle than a drunk driver. There have also been case studies that show that a person under the influence of marijuana is safer than a drunk driver, making detection more difficult.

Without the discovery of marijuana in the car, odor of marijuana in the car, or an admission by a driver that he recently smoked, police can have a difficult time evaluating if a person is stoned or not, and this could keep DUI-marijuana arrests and convictions lower than people originally predicted.