Driving high shows up in core driving tasks: THC increases lane deviations by 40%, reduces divided attention by 20–30%, and can slow reaction time by 200–700 ms. These effects help explain higher crash involvement in real-world studies, including reports that cannabis users are about twice as likely to crash. The page also compares marijuana impairment with alcohol and looks at prevalence from fatal-crash testing and youth survey results.
Key Takeaways
- Driving high impairs judgment like BAC 0.08%
- THC crash risk similar to BAC 0.05-0.08
- Marijuana twice as impairing as moderate alcohol alone
- THC impairs lane keeping, 40% more lane deviations
- Cannabis reduces divided attention by 20-30%
- THC slows reaction time by 200-700ms
- 22 states have THC per se limits like DUI BAC
- Colorado DUI drug arrests up 30% post-legalization
- 12 states set 5 ng/ml THC per se limit
- 21.5% of drivers in fatal crashes in 2018 tested positive for THC
- In Colorado, THC-positive drivers in fatal crashes increased 144% from 2013-2017
- 34% of young drivers aged 16-19 reported driving under the influence of marijuana
- Drivers high on cannabis are 2 times more likely to crash
- Cannabis increases fatal crash risk by 62% when combined with alcohol
- THC-positive drivers 1.74 odds ratio for fatal crashes
Driving high from cannabis can raise crash risk as much as or more than moderate alcohol, especially with alcohol.
Related reading
01 · Category
Comparisons27 stats
01
Driving high impairs judgment like BAC 0.08%
02
THC crash risk similar to BAC 0.05-0.08
03
Marijuana twice as impairing as moderate alcohol alone
04
Combined THC + alcohol = risk of BAC 0.15 alone
05
Per se THC limits mimic BAC 0.05 effects
06
Cannabis detection window longer than alcohol metabolism
07
Driving high reaction time = drunk at 0.07 BAC
08
THC lane weaving like BAC 0.10
09
Marijuana fatal risk 1.74 vs alcohol 1.5 at low BAC
10
High THC braking deficit > BAC 0.08
11
Cannabis + low alcohol multiplies risk 5x vs either alone
12
THC impairment duration 3h vs alcohol 2h peak
13
Per-mile fatal risk cannabis > alcohol post-legalization
14
THC 5ng/ml risk = BAC 0.05 crash odds
15
Marijuana tracking errors match BAC 0.06-0.11
16
Combined use crash risk 2x alcohol alone
17
THC novices impaired like new drinkers
18
Edibles impairment > alcohol due to delay
19
Cannabis speed control worse than BAC 0.05
20
THC visual effects similar to low-moderate alcohol
21
Dual positive drivers 3x risk vs alcohol only
22
THC chronic effects subtler than alcohol acute
23
Risk curves: THC peaks later than BAC
24
Marijuana alone less risky than high alcohol, but combo worse
25
Per se 5ng THC equiv to 0.08 BAC policy debate
26
THC fatal crashes rising faster than alcohol decline
27
Impairment equivalence: 3.5ng THC = 0.05 BAC
Interpretation
Comparisons Interpretation
Compared with alcohol, driving high can impair judgment to roughly the level of BAC 0.08 and shows a crash risk in the BAC 0.05 to 0.08 range, while marijuana can be twice as impairing as moderate alcohol and THC plus alcohol can elevate risk to about the equivalent of BAC 0.15.
02 · Category
Impairment28 stats
01
THC impairs lane keeping, 40% more lane deviations
02
Cannabis reduces divided attention by 20-30%
03
THC slows reaction time by 200-700ms
04
Smoking marijuana impairs braking response by 22%
05
High THC levels cause 18% weave in lane position
06
Edibles peak impairment lasts 3-5 hours vs 1-2 for smoking
07
Cannabis decreases alertness, 25% more speed variability
08
THC impairs night vision by 15-20%
09
Divided attention tasks impaired 27% post-cannabis
10
Peripheral vision reduced by 30% under THC influence
11
Critical tracking task performance drops 22%
12
Marijuana slows detection of hazards by 100ms
13
THC causes 16% deficit in adaptive tracking
14
Smoking 100mg THC impairs steering 2 hours
15
Cognitive impairment persists 24+ hours in novices
16
THC disrupts sleepiness countermeasures, 35% effect
17
Lane change errors increase 40% after cannabis
18
Edible THC impairs 5x longer than inhaled
19
High-potency cannabis doubles cognitive deficits
20
THC reduces gap acceptance accuracy by 28%
21
Psychomotor impairment equivalent to BAC 0.05%
22
Cannabis affects executive function, 20% error rate up
23
Visual search tasks impaired by 18%
24
THC slows stimulus discrimination by 15%
25
Memory lapses increase 25% during driving simulation
26
Dose-dependent: 2.5% THC impairs 10%, 5% 20%
27
Chronic use leads to 12% persistent lane control issues
28
THC + fatigue = 50% worse performance
Interpretation
Impairment Interpretation
For the impairment category, THC substantially degrades core driving control by raising lane deviations by about 40% and slowing reaction time by 200 to 700 ms, with higher levels also increasing lane weaving by 18% and edibles extending peak impairment for 3 to 5 hours.
03 · Category
Legal26 stats
01
22 states have THC per se limits like DUI BAC
02
Colorado DUI drug arrests up 30% post-legalization
03
12 states set 5 ng/ml THC per se limit
04
Washington THC DUI threshold 5 ng/ml since 2013
05
Nevada zero-tolerance for under-21 THC driving
06
Ohio per se 50 ng/ml whole blood THC
07
Canada federal 2-5 ng/ml THC = warning/ticket
08
18 states criminalize any detectable THC driving
09
California DUI per se 5 ng/ml post-Prop64
10
Roadside saliva tests for THC in 10 US states
11
Utah 0.05 ng/ml urine THC limit strictest
12
Post-legalization, THC citations up 200% in Oregon
13
33 states allow medical marijuana but enforce DUI laws
14
Field sobriety tests adapted for cannabis in training
15
Michigan 5 ng/ml active THC per se since 2019
16
Australia roadside oral fluid THC illegal per se
17
Europe varying limits: 1-2 ng/ml THC blood in many countries
18
Montana 5 ng/ml THC DUI law
19
Drug recognition expert (DRE) program in 50 states for cannabis
20
Legalization states see 15% rise in impaired driving arrests
21
Pennsylvania metabolite-based but active THC prosecutable
22
Blood draw warrants for THC common in DUI stops
23
7 states zero tolerance under 21 for any THC
24
Federal zero tolerance for commercial drivers THC
25
New York 5 ng/ml per se post-legalization
26
Enforcement challenges: THC lingers 30 days in chronic users
Interpretation
Legal Interpretation
From a legal standpoint, THC per se standards are spreading quickly, with 22 states adopting THC per se limits and 12 of them specifically using a 5 ng/ml threshold, while states like Colorado still report DUI drug arrests up 30% after legalization.
More related reading
04 · Category
Prevalence30 stats
01
21.5% of drivers in fatal crashes in 2018 tested positive for THC
02
In Colorado, THC-positive drivers in fatal crashes increased 144% from 2013-2017
03
34% of young drivers aged 16-19 reported driving under the influence of marijuana
04
Approximately 4.7 million people aged 12+ drove under marijuana influence in past year (2015-2018)
05
13% of US drivers self-reported driving within 2 hours of marijuana use
06
In Washington state, marijuana-positive drivers in fatal crashes rose from 8.8% to 19.6% post-legalization
07
28% of nighttime drivers had THC in system per 2013-2014 survey
08
Past-month marijuana use among drivers increased 50% from 2007-2014
09
15% of fatally injured drivers in Canada tested positive for cannabis
10
In 2020, 25% of US drivers aged 21-25 admitted to driving high
11
THC detection in 18% of weekend nighttime drivers (ROADSAFE study)
12
Marijuana use before driving reported by 22% of young adults
13
Post-legalization, THC in 30% of fatally injured drivers in Oregon
14
12% of US high school seniors drove after marijuana use
15
In Australia, 12.5% of drivers tested positive for THC roadside
16
35% increase in drivers testing positive for THC in fatal crashes 2016-2019
17
10% of drivers in Europe had cannabis in system per DRUID study
18
Self-reported driving high among 20% of past-year cannabis users
19
In California, 24% of drivers in serious crashes had THC
20
16% prevalence of THC in injured drivers (US hospital data)
21
26% of drivers aged 21-34 reported driving stoned
22
THC in 14% of fatally injured drivers under 21
23
11% of all drivers admit to driving after cannabis use
24
Post-legalization spike: 48% more THC-positive fatal crashes in states
25
19% of motor vehicle crash patients test positive for cannabis
26
23% of young drivers (18-24) drove high in last month
27
THC detection doubled in drivers from 2010-2020
28
17% prevalence in urban drivers per wastewater analysis proxy
29
29% of chronic users drive within 4 hours of use
30
In 2019, 22.1% of fatally injured drivers had THC
Interpretation
Prevalence Interpretation
Overall prevalence is high and rising, with THC-positive presence in fatal crashes reaching 21.5% in 2018 and climbing sharply in some states such as Colorado up 144% from 2013 to 2017 and Washington from 8.8% to 19.6% after legalization.
05 · Category
Risks29 stats
01
Drivers high on cannabis are 2 times more likely to crash
02
Cannabis increases fatal crash risk by 62% when combined with alcohol
03
THC-positive drivers 1.74 odds ratio for fatal crashes
04
Driving high doubles near-crash rate per naturalistic studies
05
25% higher crash risk for recent cannabis users
06
Marijuana impairment leads to 36% increased crash involvement
07
Odds of crash 2.1 times higher with THC >5 ng/ml
08
Post-legalization, fatal crash rates up 6% in cannabis states
09
Cannabis users 1.5-3 times more likely to be culpable in crashes
10
48% increased risk of fatal crashes for young drivers high
11
Driving after edibles increases crash risk by 4.3 times
12
THC impairs reaction time, increasing rear-end crashes by 20%
13
Legal cannabis states see 3.5% rise in crash rates per 10% sales increase
14
High-THC drivers 85% more likely to swerve
15
Cannabis doubles risk of single-vehicle crashes
16
2.4 odds ratio for injury crashes with recent marijuana use
17
Nighttime driving high increases fatal risk by 70%
18
Chronic users show 1.92 crash risk multiplier
19
Marijuana involved in 17% increase in teen crash deaths post-legalization
20
THC >2 ng/ml triples involvement in serious crashes
21
Driving high linked to 28% higher insurance claims
22
1.8 times greater risk of road departure crashes
23
Cannabis edibles cause 3x prolonged impairment risk
24
Young males driving high: 4x crash odds
25
55% higher fatal crash rate in first year post-legalization
26
THC and speed combo increases risk by 92%
27
Marijuana doubles hospital admission for MVCs
28
2.7x risk for intersection crashes when high
29
Post-2018 legalization, 10% uptick in drug-related fatalities
Interpretation
Risks Interpretation
From a risks perspective, being high on cannabis is linked to markedly higher driving danger, with crash risk doubling in near miss studies and a 62% rise in fatal crashes when combined with alcohol.
Reference
Cite This Report
This report is designed to be cited. We maintain stable URLs and versioned verification dates. Copy the format appropriate for your publication below.
APA
Karl Becker. (2026, February 13). Driving High Statistics. Gitnux. https://gitnux.org/driving-high-statistics
MLA
Karl Becker. "Driving High Statistics." Gitnux, 13 Feb 2026, https://gitnux.org/driving-high-statistics.
Chicago
Karl Becker. 2026. "Driving High Statistics." Gitnux. https://gitnux.org/driving-high-statistics.
Sources & references
41 datasets cited across this report · attribution is report-level