How Does Driving Under the Marijuana Affect Your Driving Skills

Marijuana is the most commonly abused drug throughout the world. In 2009, results showed that 125-203 million people had used it in the previous year across the globe.

Bringing the matter closer home, the number of weed users in the USA might surprise you. In 2017, a survey by Marist showed that 33 million adult Americans were regular weed users.

us marijuana use by age

What’s more, the National Highway Traffic Safety Administration reports that 12.6% of weekend drivers tested positive for tetrahydrocannabinol (THC) in a 2013-2014 survey.

This is definitely a public traffic safety concern especially when driving on the roads today. As such, it’s right to get concerned about whether or not smoking weed has an influence on driving capability.

And that’s what this post will be all about.

How Does Marijuana Affect Driving

There are tons of studies that have been done around this issue, and they are mixed. Some claim that weed has the ability to impair certain abilities that are critical to safe driving including attention, cognitive actions, and reaction time.

On the other hand, some extensive studies claim to have found no direct association between the level of THC in the blood and a higher risk of crashing.

We’ll get back to these studies in a few minutes. But first, let us understand some facts about how THC (the main active ingredient in weed) affects your brain.

Some basics on how the brain works

The brain is made up of a system of communication known as the endocannabinoid system (EC). The EC system comprises of brain cells (scientifically known as neurons) that pass communication between each other in the form of chemical messages.

The neurons that release and send the message are known as presynaptic neurons, while those that receive the message are called postsynaptic neurons.

The messages are in the form of chemicals called cannabinoids and are carried by neurotransmitters through the gap between neighboring neurons.

The postsynaptic neurons, on the other hand, have a set of cannabinoid receptors onto which the cannabinoids bind thereby making the communication a success.

Now, the cannabinoid receptors regulate different functions of the brain depending on exactly where they are in the brain.

For instance, the receptors in the cerebellum are responsible for regulating motor coordination and balance, while those in the neocortex regulate complex thinking including making judgments and movements.

The receptors in the Basal Ganglia part of the brain, on the other hand, are responsible for planning and starting movements.

What weed does in the brain

When you eat or smoke weed, THC (Tetrahydrocannabinol – the main active ingredient in weed) is eventually absorbed into the blood system where it is circulated all around the body organs including the brain.

In the brain, THC acts specifically on the cannabinoid receptors that are intrinsically meant to respond to THC-like chemicals.

When THC over activates the sections of the brain with the most cannabinoid receptors, what follows is the ‘High’ effect that weed causes.

Binding to the cannabinoid receptors also means that THC interferes with the natural interplay between the neurons. As such, the strength of the signals is altered by causing ineffective communication in the entire endocannabinoid system.

This is what causes the short-term effects of weed including an altered sense of time, impaired memory, changes in mood, and difficulties with solving problems.

Marijuana and Driving – Scientific Findings

Studies on the effects of marijuana on driving skills are generally categorized into cognitive studies and experimental studies.

Cognitive studies – as the name suggests, these studies mainly focus on the effects of THC on the cognitive processes that are generally considered vital for safe driving. These include attentiveness, vigilance, perception of time and speed, and employing acquired knowledge.

A meta-analysis of lots of studies on this subject including this study and this one conclude that pot causes significant impairment in virtually all the brain functions that are known to be necessary for safe driving.

In the latter study, 10 weed users smoked a marijuana cigarette containing 0% and 3.97% THC concentration and then started a 60-minute simulated driving test after 2 minutes. The researchers found out that the high dose caused a significant increase in body sway. They also noted an increase in brake latency which was comparable to stopping at 5 ft at 60 mph.

Experimental research studies – in these studies, the researchers measure the probability of causing an accident when driving under the influence of marijuana using either a driving course or a simulator.

Most of these studies tend to offer conflicting findings.

In this study conducted by Maastricht University, the results did not show any significant functional impairment. The researchers suggested that the reason why there is minimal risk of causing a crash when driving under the influence of marijuana is that the drivers tend to overestimate their impairment and as a result employ compensatory techniques including driving at a lower speed, overtaking fewer times, and increasing following distance.

While the behavioral responses mentioned above seem a convincing strategy to minimize the risk of crashes, other researchers opine that there are some deficits that these compensatory mechanisms might not cater to.

In one study, the researchers noted that marijuana users did not succeed in compensating for darting from lane to lane.

Another study recorded poor speedometer monitoring, while others show that the drivers under marijuana influence were not able to react to changing light and sudden obstacles on time.

Bottom line: Marijuana and Driving don’t mix

One thing that stands out from most of the studies done around this issue is that cannabis does impair certain driving skills such as tracking albeit at lower concentrations (6.25mg).

Other complex functions are only altered at higher doses but users have the ability to compensate for these deficits by driving slowly and maintaining a longer-than-normal following distance. However, there are still several functions that are hard to compensate for and which could prove disastrous.

Another important finding that most of these studies bring out is that combining alcohol and marijuana tends to double or even triple the impairment and nullify any compensatory attempts.

Unpacking Statistics on Pot Use

How many people die in car crashes related to marijuana use?

In an age where most states have legalized recreational marijuana, it’s not surprising that an increasing number of drivers after a crash often test positive for THC.

Research studies in states that have legalized recreational use of weed show a 6% increase in crashes. Although researchers are yet to settle the science on whether or not marijuana can be directly linked to the cause of the crashes, most studies have enough proof that there exists a correlation between crashes and legalization of marijuana.

Speaking to NBC News, David Harkey, president of IIHS (Insurance Institute for Highway Safety’s Highway Loss Data Institute) says that studies from police statements and insurance claims show that crashes rose by 5.2-6% in states that have legalized recreational use of marijuana compared to those that don’t.

car crashes statistics

A 2016 report by the Governor’s Highway Safety Association tends to cement these findings and shows that 38% of all the fatally-injured drivers in 2016 tested positive for marijuana only (no opioids or other drugs).

Going by a report by the National Transportation Highway Safety Administration of the same year, more than 37,000 people lost their lives to car crashes.

Of these, only 54% were tested for alcohol and drugs. And of the group that was tested, 38% of the drivers tested positive for marijuana only according to the GHSA report above. This translates to around 7,592 deaths.

marijuana positive drivers

Keep in mind that this number could have been higher since not all the fatally-injured drivers were tested for drugs and alcohol.

How many people are arrested for driving under the influence of cannabis (DUIC) in the USA?

Currently, 33 states allow the use of medical marijuana while 10 states have so far legalized its recreational use.

All in all, in Washington alone, it is estimated that about 20,000 drivers are arrested annually by State Patrol for suspicion of impaired driving.

Generally, about 1 million people are arrested all around the USA for driving under the influence of marijuana.

The number of people arrested for DUIC varies from state to state depending on what the state’s law deems as impaired driving.

Several states have so-called Per Se laws that specify a THC limit above which the driver may be considered impaired. These limits vary from state to state and can anywhere between 1 ng/ml and 5 ng/ml.

Washington, Illinois, and Montana currently have the highest limit of up to 5 nanograms per milliliter of blood, followed by West Virginia (3 ng/ml), Nevada (2 ng/ml), and Pennsylvania (1 ng/ml).

Most states such as Oregon, Idaho, Texas, and Kansas have no marijuana-specific driving law. These states have an impairment-based statute that requires the particular law enforcement agency to prove that the driver was impaired. This requires documented behavioral evidence and proof of recent use.

Several states offer no wiggle room and have zero tolerance for THC and its metabolites. These include Arizona, Utah, Oklahoma, and Georgia. Check your state’s statistics regarding marijuana-impaired driving here.

How do roadside cops test for driving impairment/driving under the influence of Marijuana?

Although most states have now legalized the use of medical and recreational marijuana, it is still an offense to drive under its influence. And this means that the cops need to device a way to determine driving impairment due to marijuana use.

Unfortunately, the law enforcers currently don’t have a breathalyzer-equivalent for cannabis impairment.

If the cops suspect that you might be impaired, they will typically require you to take a roadside sobriety test. This is a 3-part test that- among other things- requires you to stand on one leg for around 30 seconds and count aloud from 1000 as the officer looks for certain impairment indicators including swaying and overly use of arms to maintain balance.

roadside sobriety test

In most states, the law empowers the cops to demand a roadside saliva test. This is usually fast and should tell whether you are positive or negative in about 4 minutes.

If it shows positive, then the chances are that you are over the 25-ng limit that saliva tests use. However, failing the saliva test does not mean that you are impaired since it does not indicate the actual level of THC.

At this point, the cops may demand a blood test to determine the exact THC level in your blood. You also have a right to request legal counsel at this time.

It will take anywhere between 2 and 4 hours before the blood test is done. The good or bad news is that the level of THC concentration drops by 90% within the first 2 hours.

Keep in mind, however, that if the results are over 5/3/2/1 ng (depending on your state’s per se laws), it is generally argued that the concentration was higher when the police pulled you over.

Consequences of driving under the influence; Jail Term, Fine, and License Suspension

If you are convicted for being behind the wheel while under the influence of cannabis, here is a summary of the possible penalties including license suspension period;

DUIC Offense Possible Penalty
1st offense Jail term: 6 months or

Fine: $390-$1,000 or

DUI school: 9 months

License suspension: 6-10 months (convertible to license restriction)

2nd offense Jail term: 96 hours- 1 year or

Fine: $390-$1,000 or

DUI school: 2 years

License suspension: 2 years (convertible to license restriction after 12 months)

3rd offense Jail term: 120 days- 1 year

Fine: $390-$1,000

DUI school: 30 months

License suspension: 3 years (convertible to license restriction after 18 months)

Misdemeanor DUI offense with injuries Jail term: 5 days- 1 year

Fine: $390- $5,000 plus compensation to injured parties

DUI school: 3-18 months

License revoked- 1-3 years

Felony DUI Jail term: 16 months, or 2 or 3 years

Fine: $390-$1,000

DUI school: 18-30 months

License revoked: 4 years

Felony DUI with injuries Jail term: 16 months – 16 years

Fine: $1,015- $5,000 plus compensation to injured parties

DUI school: 18-30 months

License revoked: 5 years

Impact of driving under marijuana influence on insurance

Insurance companies are always on the lookout for new ways to mitigate risk and possible losses.

Considering the surge in fatalities due to marijuana-impaired driving, the legalization of weed is definitely one of the factors that most insurance companies are considering when determining your premiums.

Actually, most insurance companies seem to have already implemented this. Case in point: Colorado. A study conducted by The Denver Post shows that there were 47 fatalities only in 2013.

Come 2016, this number had shot up by 147% to a total of 115 fatalities. The study notes that of the percentage of drivers who tested positive for THC had shot from 10% to 20%.

The Post also states that insurance premiums rose by 50% in the last 6 years following the legalization of weed.

It’s quite unfair that these rates apply for everyone including those who don’t consume marijuana. If you are among these, you might want to scour a little bit harder for a fairer insurance quote especially because all companies have a different perspective on the factors that determine your premium.

How long after smoking weed can you drive?

You’ll come across lots of suggestions on this issue – most sources suggest a minimum of 2 hours. Unfortunately, the existing scientific evidence doesn’t draw a clear line on how long one would need to wait after smoking to drive.

A recent study by McGill University researchers seems to have a critical insight, though. This study comprised of 45 cannabis consumers who inhaled 100mg of weed before being put into a driving test after the 1st, 3rd, and 5th hour after toking.

This study first affirmed that THC has a significant impairment on the most important driving-related skills. But it also noted that the effects could be felt up to 5 hours after smoking.

Basically, this study suggests that you should avoid the wheel for at least 6 hours after getting stoned. Other external studies, however, claim that the effects can be felt up to 24 hours after smoking.

These contradicting suggestions all tend to mean that there is no magical number that will work for everyone. This emanates from the fact that weed affects its users differently depending on a number of factors including weight, experience, how long one has smoked, how much one has consumed, as well as the concentration of the strain.

Mike Serr, Chief Constable, Abbotsford Police Department and chair of the Canadian Association of Chiefs of Police Drug Advisory Committee advises seeking another way of getting home after consuming marijuana.

Parent’s Liability

What if your son is caught driving while high on marijuana, what’s your fate as the parent?

Well, in such an occurrence, whether or not you are going to face criminal liability depends on the situation. Generally, if there’s enough evidence that you either knew of the child’s drug use, supplied, or exposed the child to the drugs, you can be arrested and made to face criminal charges.

On the other hand, you don’t need to worry about a thing as long as you didn’t provide the drugs or didn’t know about the child’s drug usage.

When a child is arrested for pretty much any criminal act, it’s naturally hard for the parent to accept that the child is guilty. Understand, however, that not all minors who are arrested for a certain crime are always innocent.

Therefore, the best thing would be to remain calm and seek legal counsel immediately. Never allow the child to talk to the police without a lawyer.

Importantly, never allow the law enforcers to search your house or vehicle without a warrant even if you are pretty sure that you are clean. Otherwise, you could lose your property or car in court proceedings that ensue in case drugs are uncovered.

Parental responsibility laws for delinquent youth vary from state to state. Some states such as Texas, Kansas, and Michigan have less stringent laws and only require the parent to attend the child’s court hearings or face contempt charges.

If you live in Alabama, Kentucky, Kansas, and West Virginia, the law requires you to pay for all the court costs associated with your child’s proceedings.

Other states including Indiana, Virginia, Idaho, Florida, and North Carolina require you to reimburse the state for all the costs incurred in the detention, treatment, support, and care of the youth.


What if the cops claim that they smell weed in your car but you’ve never smoked marijuana, what do you do to prove your innocence?

While the fourth amendment protects us from unwarranted governmental searches in our homes and in public, an overt smell of marijuana from your vehicle is enough reason for the police to carry out a search even without a warrant.

Now, smell alone is not enough to put you in trouble; the law enforcement will need to have solid evidence to incriminate you. But the cops often mention weed just as a trick to see your reactions more so if you look suspicious and draw their attention.

That being said, the best thing is to remain calm and avoid looking nervous. You could also tell the police that you have nothing to hide, but you won’t consent for a search. If they insist, though, you might want to step aside and let them do their thing. However, if they find something, arrange for an attorney immediately to help you out with the charges.

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