Every year, lives are lost on roads that did not have to be. Public conversation around road safety has long centred on alcohol. Now, a growing body of research is turning attention to driving after cannabis use and the dangers it creates for everyone on the road.

New findings from the Colorado School of Public Health (CSPH) are difficult to ignore. Researchers used a sophisticated driving simulator to measure how cannabis affects vehicle control. The results are sobering.

Driving After Cannabis Use: What the Statistics Show

Colorado has allowed recreational cannabis since 2012. It offers a revealing snapshot of what widespread use means for road safety. According to 2024 data from the Colorado Department of Public Health:

• 16.3% of cannabis users reported driving within two to three hours of consuming it
• 45 people died in crashes involving an at-fault driver impaired by cannabis in a single year
• Combined drug and alcohol fatalities have climbed from 26% to 32% since 2017

About one in five Coloradans used cannabis in the past 30 days. Half of those do so daily. That scale of use makes the road safety picture hard to overlook.

Cannabis Use Behind the Wheel Is Not Like Drink Driving

It would be wrong to assume driving after cannabis use looks the same as drink driving. Associate Professor Ashley Brooks-Russell leads the driving research at CSPH. She says the behavioural patterns differ considerably.

“Alcohol-impaired drivers tend to be aggressive,” she noted. “We don’t see that same pattern with cannabis drivers, but even so, cannabis use can still increase risk.”

Cannabis users may not feel obviously impaired. Not in the way someone heavily intoxicated with alcohol might. Yet the research shows driving performance still deteriorates in measurable ways.

Edibles and Cannabis Use Behind the Wheel: A Hidden Danger

The CSPH study looked at both inhaled cannabis and edibles. The difference matters a great deal when it comes to road safety.

Inhaled cannabis takes effect almost immediately. Edibles work differently. They are processed through the digestive system. Onset can be delayed by an hour or more. Effects also last considerably longer.

This creates a dangerous gap. A person who has eaten a cannabis edible may feel fine when they sit behind the wheel. Then the effects intensify once they are already moving. Impairment from edibles can last several hours.

“Edibles are processed through the digestive system, so the onset is slower, and the effects last longer,” Brooks-Russell explained. “When people don’t feel impaired right away, they may consume more than intended.”

What the Simulator Revealed About Driving After Cannabis Use

Researchers placed participants in a highly realistic driving simulator. It had a steering wheel, pedals, a dashboard and a large touchscreen for music and messages. Three widescreen monitors created a 180-degree field of view.

Each participant completed a sober baseline drive. Then two further drives after consuming cannabis. The team measured lane weaving, lane departures and how steadily drivers held their position.

The edible group showed the most concerning results. They drove at reduced speed. They also showed more lane weaving and more frequent departures from their lane.

“At those higher speeds, we tend to see more pronounced differences,” Brooks-Russell said.

Occasional users showed more impairment than daily users. That points to the role tolerance plays. But tolerance is not a safety guarantee.

Tolerance Does Not Make Cannabis Use Behind the Wheel Safe

Daily users showed less measurable impairment in some areas. That sounds reassuring. It is not.

Tolerance does not eliminate the effects of cannabis. It masks them. The risks of driving after cannabis use remain for regular users too. A lapse in judgement on the road can still be fatal.

Researchers caution strongly against using tolerance as a reason to drive.

Older Drivers and Driving After Cannabis Use

A separate ongoing study at CSPH is examining drivers aged 65 and over. Professor Carolyn DiGuiseppi is leading the research. It focuses on older adults who may have some mild cognitive decline. That is a common part of ageing, not a clinical diagnosis.

Cannabis use among older adults has grown in recent years. Many turn to it for pain relief or other perceived health benefits. The risks of driving after cannabis use do not shrink with age. In some cases they may grow.

“Whether they are using cannabis medicinally or recreationally, we need to know the risks,” DiGuiseppi said.

No Roadside Test for Cannabis Use Behind the Wheel

One of the biggest challenges is the lack of a reliable roadside test. There is nothing equivalent to the breathalyser for alcohol. Cannabis can stay in the bloodstream long after the psychoactive effects have faded. That makes it very hard to confirm impairment at any given moment.

Legal guidelines remain unclear in many places. That ambiguity can give drivers a false sense of security. If impairment is hard to measure, some assume it must not be there. The research says otherwise.

The Bottom Line

The evidence is consistent. It points one way. Driving after cannabis use is a genuine and growing road safety concern. That is true whether you use occasionally or daily, whether you inhale or eat it.

“We each have a responsibility to drive safely,” Brooks-Russell said. “If you feel impaired, you shouldn’t drive.”

The choice is straightforward. Roads are safer when people make better decisions before they turn the key.

Source: dbrecoveryresources