Tag Archives: marijuana

Appropriate testing for marijuana-impaired drivers

Methods for testing the level of a driver’s possible impairment from marijuana is more complex than a simple blood level of the substance. Some states in which marijuana is legal are apparently using tests which could produce flawed results. Other states are set to follow their example.

The foundation recommends replacing the laws with ones that rely on specially trained police officers to determine if a driver is impaired, backed up by a test for the presence of THC rather than a specific threshold. The officers are supposed to screen for dozens of indicators of drug use, from pupil dilation and tongue color to behavior. Study: No scientific basis for laws on marijuana and driving

Here is yet another example of a traffic safety problem which could be addressed more effectively through a White House Vision Zero Task Force. Then, once such a Task Force were to recommend an appropriate law and testing technique, all states could be required to follow suit–without having to reinvent the wheel 50 time over.

Why on earth don’t we establish National Traffic Safety Standards & require them to be adopted by States?

Vision Zero Goal


Marijuana Impairs Judgment, Reaction Times, & Awareness

What will be the impact of increased use of marijuana on road safety?

NHTSA recently commented on this question ( http://ht.ly/IDHau )  :

“. . . even as drinking and driving continues to fall, use of illegal drugs or medicines that can affect road safety is climbing. The number of weekend nighttime drivers with evidence of drugs in their system climbed from 16.3 percent in 2007 to 20 percent in 2014. The number of drivers with marijuana in their system grew by nearly 50 percent.

A second survey, the largest of its kind ever conducted, assessed whether marijuana use by drivers is associated with greater risk of crashes. The survey found that marijuana users are more likely to be involved in accidents, but that the increased risk may be due in part because marijuana users are more likely to be in groups at higher risk of crashes. In particular, marijuana users are more likely to be young men – a group already at high risk.

This was the most precisely controlled study of its kind yet conducted, but it measured the risk associated with marijuana at the levels found among drivers in a large community. Other studies using driving simulators and test tracks have found that marijuana at sufficient dosage levels will affect driver risk.

Drivers should never get behind the wheel impaired, and we know that marijuana impairs judgment, reaction times and awareness,’ said Jeff Michael, NHTSA’s associate administrator for research and program development. ‘These findings highlight the importance of research to better understand how marijuana use affects drivers so states and communities can craft the best safety policies.’

The study, conducted in Virginia Beach, Va., gathered data over a 20-month period from more than 3,000 drivers who were involved in crashes, as well as a comparison group of 6,000 drivers who did not crash. The study found that drivers who had been drinking above the 0.08 percent legal limit had about 4 times the risk of crashing as sober drivers and those with blood alcohol levels at 0.15 percent or higher had 12 times the risk.

NHTSA plans a series of additional studies to further understand the risk of drugged driving, including the Washington State Roadside Survey, which will assess risk in a state where marijuana has recently been legalized, and a simulator study with the National Institute on Drug Abuse to assess how drivers under the influence of drugs behave behind the wheel.”

More sources:



(Photo is of our car hit by a truck and pushed under another truck; marijuana was not cited as a cause, but truck driver fatigue might have been a factor which also impairs driving reaction times.)