According to the biggest meta-study to date, driving under the influence of cannabis (and no other drug) increases risk about 1.8 times.
Drivers with a blood alcohol level of 0.02 BAC have a risk of fatal collision ~4 times greater than sober drivers.
A blood alcohol level of 0.08 BAC increases risk of fatality ~13 times, driving with a BAC of 0.12 increases risk by ~25 times, and a BAC of 0.16 increases risk ~35 times.
Cannabis plus alcohol increases risk by ~23 times.
http://www.wigmoreonalcohol.com/meta-analysis-of-fmvc-risk-at-low-bac/
You've proabbly seen stuff recently in the media, about a significant increase in the number of drivers detected with cannabis in their system in Washington State in the last year, (since cannabis use was legalised).
The data from Washington led to articles like this one-
http://www.csmonitor.com/USA/Latest...-arrested-for-DUI-A-record-high-in-Washington
But, as usual, the devil is in the details-
<<< In the past two years, the annual total each year for positive marijuana blood tests in Washington is about 1,000. In 2011, there were 506 tests >5ng. In 2012, there were 609 tests >5ng. Overall impaired driving cases, however, are on pace to hit the annual average of about 20,000.
Based on those data, we find the Christian Science Monitor proclaiming “Pot smokers arrested for DUI: A record high in Washington”. Well, that’s not exactly true. To get a blood test, cops must make a DUI arrest and get a warrant, and in years past, about 1,000 tested positive for THC. But before legalization, all those positive tests – at any amount, not just over 5ng – were evidence used to convict on DUI charges. Now, any test below 5ng is proof a driver was below the legal limit. The 420 tests above the 5ng limit work out to 840 DUIs for the year, below the 1,000 any-amount DUIs of the past. >>> (see third link below for more discussion).
Medical Daily led with similar headlines to CSM,
http://www.medicaldaily.com/more-wa...e-pot-following-marijuana-legalization-263633 dramatically misreading the data and falsely describing an increase of x 1.49 (from 1,000 THC positives in a year, to 745 THC positives in six months) as a “threefold increase”.
Neither article mentions that according to Washington State’s Traffic Safety Commission “Target Zero” data for 2013, the fatality rate from incidents involving drunk and/or drug-affected drivers is actually the LOWEST that has been recorded in more than seven years.
Download the quarterly data here;
http://www.wtsc.wa.gov/statistics-reports/crash-data/
So far, the 2013 fatality rate is down 22% for alcohol-related road deaths, and down 30% for other-drug-related road deaths, compared to 2012.
If more people really are driving whilst seriously impaired, why is there no spike in road fatalities?
Well, the most probable reason is that there hasn't been a significant increase in the number of stoned drivers, the data is a product of the fact that police in Washington State have conducted significantly more drug tests in 2013 than in previous years.
But don’t take my word for it- that last piece of information comes from Bob Caulkins, the Media & Community Relations Officer for the Washington State Patrol;
<<< However, the number of tests being ordered has increased, on pace for 180 more than the prior year. It can also be true that cops are more likely to order a blood test in a pot case now. As Caulkins told Huffington Post, “We’re testing blood we didn’t test before.” So do we actually have more stoned drivers on the road or are cops now just better trained and incentivized to go after them? Just because you’re catching more fish doesn’t mean there are more fish; you may just be using a bigger net, fishing longer hours, and picking a better spot to fish.
The real concern isn’t whether there are more drivers caught with THC in their system; that’s not terribly surprising given the state has legalized marijuana. The concern is whether harm has increased. On that front, we see in the various reports that the Washington State Patrol is on pace for their average 20,000 impaired driver stops, so it doesn’t seem like their seeing more impairment on the roads than before. The “on pace” suggests that they’re at about 10,000 stops over six months. So, out of 10,000 stops, cops only felt the need to order a blood test about a quarter of the time and found 420 people over the legal THC limit.
According to Washington State’s Traffic Safety Commission “Target Zero” data for 2013, the state is on pace to record 88 alcohol-related traffic fatalities and 80 drug-related fatalities for the year. Those would be the lowest figures for both for the last five years and a decline of 22% for alcohol and 30% for drugs from 2012. Could it be that greater access to marijuana equals less abuse of alcohol, leading to lower traffic deaths from both?
It is certainly the case that stoned drivers are far better drivers than drunk drivers, but they are also far better than drivers using certain legal prescription medications. According to research published this year in the journal Accident Analysis and Prevention, drivers who tested positive for marijuana had an odds ratio of 1.81:1 of being in a fatal crash compared to a sober (1:1) driver. Those odds were 3.03:1 for narcotics like Vicodin, 3.57:1 for stimulants like Adderall, and 4.83:1 for depressants like Ativan, but each carries a warning on the bottle instructing users not to drive until they know how the medication affects them. None of those drugs carries any per se threshold in a blood test indicating automatic proof of impairment like cannabis and alcohol do. Alcohol comes in with an astounding 13.64:1 odds ratio for a fatal crash, so if some of those drivers are switching to the drug with the 1.81:1 risk, we should all be celebrating… >>>
Click here for some more informed discussion;
http://www.theweedblog.com/washington-cops-find-420-stoned-drivers-really/
Of course the same argument was levelled at “medical marijuana” laws, and appears to have been refuted;
<<< States that legalize medical marijuana see fewer fatal car accidents, according to a new study, in part because people may be substituting marijuana smoking for drinking alcohol.
Sixteen states and the District of Columbia, have legalized medical marijuana since the mid-1990s. For the new study, economists looked at 1990-2009 government data on marijuana use and traffic deaths in the 13 states that had passed legalization laws during that time period. The data were from the National Household Survey on Drug Use and Health and the National Highway Traffic Safety Administration.
Comparing traffic deaths over time in states with and without medical marijuana law changes, the researchers found that fatal car wrecks dropped by 9% in states that legalized medical use — which was largely attributable to a decline in drunk driving. The researchers controlled for other factors like changes in driving laws and the number of miles driven that could affect the results.
Medical marijuana laws were not significantly linked with changes in daytime crash rates or those that didn’t involve alcohol. But the rate of fatal crashes in which a driver had consumed any alcohol dropped 12% after medical marijuana was legalized, and crashes involving high levels of alcohol consumption fell 14%.
Read more: Why Medical Marijuana Laws Reduce Traffic Deaths | TIME.com
http://healthland.time.com/2011/12/...ana-laws-reduce-traffic-deaths/#ixzz2nh80k53i >>>
Here’s the study that last article is referencing;
http://www.ucdenver.edu/academics/c...conomics/research/Documents/Rees_WP_11-05.pdf
<<< Specifically, we find that traffic fatalities fall by nearly 9 percent after the legalization of medical marijuana. >>>
RE: relative risks, alcohol, other drugs, and driving;
Drug use and fatal motor vehicle crashes:
A case-control study.
Guohua Li et al
Accident Analysis and Prevention Sept 2013
<<< ABSTRACT Drugged driving is a serious safety concern, but its role in motor vehicle crashes has not been adequately studied. Using a case-control design, the authors assessed the association between drug use and fatal crash risk. Cases (n=737) were drivers who were involved in fatal motor vehicle crashes in the continental United States during specific time periods in 2007, and controls (n=7719) were participants of the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers. Overall, 31.9% of the cases and 13.7% of the controls tested positive for at least one non-alcohol drug. The estimated odds ratios of fatal crash involvement associated with specific drug categories were 1.83 [95% confidence interval (CI): 1.39, 2.39] for marijuana, 3.03 (95% CI: 2.00, 4.48) for narcotics, 3.57 (95% CI: 2.63, 4.76) for stimulants, and 4.83 (95% CI: 3.18, 7.21) for depressants. Drivers who tested positive for both alcohol and drugs were at substantially heightened risk relative to those using neither alcohol nor drugs (Odds Ratio=23.24; 95% CI: 17.79, 30.28). These results indicate that drug use is associated with a significantly increased risk of fatal crash involvement, particularly when used in combination with alcohol. >>>
Full text available;
http://www.uniad.org.br/desenvolvimento/images/Drug_Use_and_Fatal_MVC_CaseControlStudy.pdf
Drivers who tested positive for cannabis (detected either as actual THC in blood or THC-COOH metabolites in saliva) were found to have a 1.81:1 odds ratio – this equates to roughly an 81% greater chance of a fatal accident. Another way to express this is that a driver’s current cannabis intoxication increases the risk of road fatality by 1.8 times.
The study also examined prescribed pharmaceuticals and illicit drugs in the following classes;
Opioids such as morphine, oxycodone and hydrocodone were found to have an odds ratio of 3.03:1, ( or three times the risk) of fatal crash.
Stimulants such as methamphetamine, dexamphetamine, methylphenidate and phentermine have a 3.57:1 odds ratio, ( >three and a half times the risk)
Benzodiazepines such as valium or alprazolam registered a 4.83:1 risk, (nearly five times the risk).
The study compared these risk levels to alcohol, alone and in combination with other substances;
Alcohol, absent any other drug in the driver’s system, had an odds ratio of 13.64:1 (more than thirteen and a half times the risk of a sober driver).
This risk was even worse in drivers with alcohol and other drugs in their system- averaged over all it was 3.41:1.
Cannabis plus alcohol recorded the highest risk of all- this combination had an odds ratio of 23.24:1.
Just to put these figures into perspective, cannabis alone increased the risk of a fatal collision by 1.8 times.
Drivers with a blood alcohol level of 0.02 BAC have a risk of fatal collision 4 times greater than sober drivers.
(Of course, in Australia we let people with a BAC of up to 0.05 drive on our roads every day).
A blood alcohol level of 0.08 BAC increases risk of fatality 13 times.
(In many US states this is still the legal limit).
A BAC of 0.12 increases risk by 25 times.
A BAC of 0.16 increases risk 35 times.
http://www.wigmoreonalcohol.com/meta-analysis-of-fmvc-risk-at-low-bac/
Alcohol intoxication is responsible for approximately ¼ of all motor vehicle fatalities.
There is an excellent discussion of cannabis, alcohol, and motor vehicle fatalities, including some of the confounders, (such as age and gender), and the uncertainties (eg serum levels of THC are a less effective measure of impairment than blood alcohol levels), here;
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2722956/
Please be aware that I do not endorse driving under the influence of any psychoactive drug. Except perhaps coffee.
Please be aware that I do endorse and advocate for evidence-based policy.
Regards,
Outrigger.
