Usage of marijuana doubles chances of severe motor vehicle accidents

Forget about the joys of pot: driving within three hours after smoking marijuana increases your likelihood of causing a severe car crash.
Thanks to observational studies done by researchers in Canada, the world's most popular illegal substance could join sleep deprivation and alcohol consumption as a widely-acknowledged contributor to driver impairment.
A research team from Dalhousie University recently pioneered a meta-analysis of drivers who were killed or seriously injured in a motor vehicle accident.
After reviewing a total of nine studies and 49,411 drivers, they determined that cannabis consumption nearly doubled the risk of a motor vehicle collision.
Unlike previous studies, the analysis avoided mixed results by examining drivers who took cannabis prior to driving but were not under the influence of alcohol and other substances.
The study obtained its results through blood samples and self-report. It focused on accidents that occurred on public roads and involved one or more moving vehicles, such as cars, vans, buses and motorcycles.
While the researchers did not explore the effects of dosage on the risk and severity of collisions, the fatally-injured drivers they examined had high levels of tetrahydrocannabionol (THC), an active compound in marijuana, in their blood. This indicated that the drivers either consumed marijuana shortly before driving, or smoked a large quantity of it. Of the three studies that measured for THC levels in blood, all of them revealed a positive correlation between the risk of a car crash and elevated blood THC concentrations.
However, the researchers maintain that more evidence is needed to confirm what levels of THC are needed to cause driving impairment, as well as whether cannabis contributes to minor collisions.
Marijuana use has been increasing in recent years, and a greater number of drivers are driving under its influence. In 2004, a Canadian study found that four percent of adults reported driving within an hour of using pot. A roadside survey in 2007 indicated that 15 percent of Scotland drivers aged 17-39 admitted to consuming cannabis within 12 hours of driving.
According to professor Wayne Hall from the University of Queensland Centre for Clinical Research, although the level of impairment from smoking pot is not as severe as alcohol intoxication, a public health response is warranted.
However, Hall also claims that it is unclear whether roadside drug testing is effective. Most states and territories in Australia implement a drug-testing policy, but, as of now, no one has attempted to assess its effectiveness toward detecting drivers under the influence of cannabis.
The problem arises from the fact that roadside drug testing relies on the success of random breath testing. While it is easy to measure blood alcohol levels using a breath test, it is difficult to gauge impairment using concentrations of THC in saliva.
As a result, governments have often ignored the problem of defining boundaries for driving impairment by adopting a zero-tolerance policy.
In addition, roadside testing has not been as widely implemented or as well-publicized as random breath testing. To supplement their findings, Hall believes that the researchers need to know the extent to which cannabis users are deterred from driving when they use cannabis.
This, in turn, can help determine whether the roadside tests will successfully deter people from driving while drugged.
Finally, the researchers found that drivers under the age of 35 have the greatest risk of getting involved in a vehicle collision after smoking marijuana.
This reinforces Hall's belief that cannabis-detection protocols should be oriented toward younger drivers, since cannabis use is the highest in that population.
The researchers hope that these findings will encourage countries to introduce better drug-testing protocols to better ensure safety on the roads.
These findings support previous evidence that cannabis impairs motor skills needed for safe driving, suggesting that the general driving population will have lower incidences of severe collisions in comparison to those driving under the influence of cannabis.