Texas residents may be aware that several states voted in November to legalize marijuana. As the criminal restrictions on marijuana use are lifted around the country, some people worry that there could be more and more stoned drivers on the roads. After Washington legalized recreational marijuana, the rate of fatal car accidents involving marijuana intoxication doubled, according to a study by the AAA Foundation for Traffic Safety.
The same AAA study that found the fatal crash statistic also found that there is no reliable method for measuring marijuana intoxication. The organization believes that there is no scientific evidence to back up a theory that drivers become impaired after ingesting a specific quantity of THC. States that have imposed legal limits for THC on drivers may have chosen them arbitrarily.
The reason marijuana tests cannot measure intoxication reliably is that the substance affects every person differently. A specific amount of marijuana could be okay for one driver but cause another driver to become severely impaired. Another problem with roadside marijuana tests is that they can detect marijuana long after a person used the drug. The THC metabolites that are measured during drug tests could still be found in a person's blood and urine weeks after the person smoked marijuana.
There is much less dispute over the blood-alcohol limit for drivers, as specific quantities of alcohol affect people more reliably than specific quantities of marijuana. However, the tests for alcohol impairment can be faulty, and people may still argue that they were not intoxicated by alcohol after failing a breath or blood test. One drunk driving defense that attorneys often use is that a test result is unreliable because it was within a margin of error.