Ever since marijuana was legalized in Colorado, there have been loud voices of prohibitionists who say that the result of legalizing will be roads filled with stoned drivers who pose a threat to everyone on the road. So far, the numbers do not add up to the claims of the anti-drug warriors.Lara Herzog

Opponents point out that when Colorado legalized medical marijuana in 2001, there was a large increase in the number of drivers found to have smoked marijuana. There are also the studies which show that in other states that have legalized marijuana for medical purposes, there has been an increase in the number of drivers testing positive for marijuana who were involved in fatal car crashes. SAM, the anti-pot group, recently pointed out that even before Washington opened it’s first legal marijuana store, the number of drivers who tested positive for marijuana use increased by a third.

The major problem with these types of criticisms is that there is no way to accurately test how high someone is in the same way that the police can use a breathalyzer to determine how much alcohol is in a person’s body. For the roadside tests, they only detect the presence of marijuana metabolites, not for inebriation. However if a blood test is taken at a hospital, it can measure THC, the psychoactive ingredient in marijuana. There are problems with this type of testing as well, because a regular user of marijuana can still have remnant THC in their blood far after the effects have worn off. Regular users can also have levels above the legal limit, but still be able to drive just fine.

The law in Colorado says that a THC level of 5 nanograms or more results in a presumptive DUI charge. When studies cite “marijuana related” accidents, it could refer to any measure or trace of the drug. Since the roadside tests can only detect metabolites, it can only inform the police if the person has smoked within the past few days or weeks. It is because of this that it makes sense that a loosening of restrictions on marijuana would result in the higher percentages of drivers involved in fatal accidents having smoked marijuana at some point in the past few weeks or days. This kind of rise in percentage could also be expected to happen when you have any large sampling of people tested to have marijuana in their system. So the numbers do not necessarily mean that marijuana has been the cause of more accidents.


Since testing the drivers does not give a good idea of what effect legalization is actually having, it is better to look at the traffic stats since legalization took place, which is since January of this year. So far, traffic fatalities have generally declined since legalization went into effect.

The decline is continuing, with the number of traffic fatalities at 258 this year, down from only 263 last year(during the same period). It could even be considered evidence that legalization may increase road safety, as more people will choose to consume marijuana instead of alcohol. Legalization has already been shown to correlate with reduced violent crime rates. Complete prohibition also hinders science into curing cancer, with 123 studies still showing the effective use of THC and CBD against cancer.