Clear Rule

The rules around marijuana use can be confusing. But when it comes to marijuana use and driving, all you need to remember is one clear rule:

Driving impaired is illegal everywhere.

Driving impaired is illegal everywhere.

Everything else can get kind of hazy.

When you feel different, you drive different. Everything else can get kind of hazy. So, if you want to think through some of the things experts and leading researchers are learning about marijuana’s effect on your driving, you can do that here.
Index
Issue
5
Slowed Reaction Time
Subject

Studies show marijuana use slows both driver reaction time and responses to road emergencies.

Why it matters?

In driving simulator studies, drivers under the influence of marijuana were not able to successfully stay within their lanes, an effect that increased with higher doses of THC (the psychoactive ingredient in marijuana). This is a measure that is not subject to conscious compensatory mechanisms in the way that other aspects of driving can be.

Some studies have found, when compared to a sober control group, poorer monitoring of the speedometer under the influence of marijuana, increased decision time when passing, increased time needed to brake when a light suddenly changes, and increased time to respond to a changing light or sudden sound. Drivers also crashed more frequently into a sudden obstacle on a high dose of marijuana.

Related Issues: Increased Crash Risk2 Severity of Impairment6 THC and Impairment3

Clarity Level
High
Abstract
This study reviews the scientific evidence on the effects on driving while intoxicated with marijuana and contrast this with the effects of alcohol intoxication.
Abstract
This study reviews the scientific evidence on the effects on driving while intoxicated with marijuana and contrast this with the effects of alcohol intoxication.
This ranking indicates how “settled” we feel an issue is. Issues that are clear-cut, fully-researched, and conclusive have a “High” clarity level. Issues that are involved in ongoing research, or focus on matters that require additional study, have “Medium” or “Low” clarity levels — depending on the amount and strength of supporting research.