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Figure 1.
Relative Risk of Traffic Crash on April 20
Relative Risk of Traffic Crash on April 20

Forest plot showing relative increase in risk of a traffic crash on April 20 compared with control days exactly 1 week earlier and later. Solid squares indicate point estimate; relative dimensions, sample size; and horizontal lines, 95% CIs. Vertical columns show total counts between 4:20 PM and 11:59 PM on April 20 and control days. Main findings show an increase in relative risk on April 20, no significant contrary findings, and an accentuated effect for younger individuals. State-level estimates of the prevalence of marijuana use among adults from the 2002-2003 National Surveys on Drug Use and Health (near the midpoint of our study) were used to categorize states as "Higher use" (median and above) and "Less high use" (below the median).

Figure 2.
National Variation in Relative Risk of Traffic Crash On April 20
National Variation in Relative Risk of Traffic Crash On April 20

The map displays the United States for all contiguous states and offset images for noncontiguous states. Colors denote relative increase in traffic risks on April 20 compared with control days exactly 1 week earlier and later. Green corresponds to increased relative risk, yellow to neutral relative risk, and brown to decreased relative risk (spectrum scaled by logarithm transformation). Findings show that 30 states had a relative risk point estimate greater than unity (eg, Hawaii), while only 18 states had an estimate less than unity (eg, Minnesota), and 2 states had an estimate of exactly unity (eg, Montana).

1.
Burke  K. Marijuana sales on 4/20 hit record highs. MarketWatch. June 14, 2016. http://www.marketwatch.com/story/marijuana-sales-on-420-hit-record-highs-2016-06-14. Accessed September 14, 2017.
2.
Bravo  AJ, Pearson  MR, Conner  BT, Parnes  JE.  Is 4/20 an event-specific marijuana holiday? a daily diary investigation of marijuana use and consequences among college students.  J Stud Alcohol Drugs. 2017;78(1):134-139.PubMedGoogle ScholarCrossref
3.
Record crowds of 80,000 descend upon Denver to mark historic 4/20 celebration of marijuana becoming legal in Colorado. Mail Online. April 20, 2014. http://www.dailymail.co.uk/news/article-2608727/Record-crowds-80-000-descend-Denver-mark-historic-4-20-celebration-marijuana-legal-Colorado-against-law-smoke-public.html. August 9, 2017.
4.
Hartman  RL, Brown  TL, Milavetz  G,  et al.  Cannabis effects on driving lateral control with and without alcohol.  Drug Alcohol Depend. 2015;154:25-37.PubMedGoogle ScholarCrossref
5.
Whitehill  JM, Rivara  FP, Moreno  MA.  Marijuana-using drivers, alcohol-using drivers, and their passengers: prevalence and risk factors among underage college students.  JAMA Pediatr. 2014;168(7):618-624.PubMedGoogle ScholarCrossref
6.
Redelmeier  DA, Stewart  CL.  Driving fatalities on Super Bowl Sunday.  N Engl J Med. 2003;348(4):368-369.PubMedGoogle ScholarCrossref
Research Letter
April 2018

The April 20 Cannabis Celebration and Fatal Traffic Crashes in the United States

Author Affiliations
  • 1Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
  • 2Centre for Clinical Epidemiology & Evaluation, Vancouver, British Columbia, Canada
  • 3Centre for Health Evaluation & Outcome Sciences (CHÉOS), Vancouver, British Columbia, Canada
  • 4Department of Medicine, University of Toronto, Toronto, Ontario, Canada
  • 5Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada
  • 6Division of General Internal Medicine, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
JAMA Intern Med. 2018;178(4):569-572. doi:10.1001/jamainternmed.2017.8298

On April 20 each year, thousands of Americans celebrate the intoxicating properties of marijuana on a popular counterculture holiday known as “4/20.” Legal marijuana sales surge in anticipation of the “High Holiday,” and college students report increased cannabis consumption on 4/20 itself.1,2 In many cities, activists and enthusiasts gather at public celebrations that feature synchronized mass consumption of cannabis at 4:20 pm.3

Driving simulation studies indicate that higher blood Δ9-tetrahydrocannabinol concentrations decrease reaction times and increase variability in speed and lane position, while some epidemiologic studies suggest that acute cannabis intoxication increases crash risk.4 Despite this evidence, driving after cannabis consumption is surprisingly common.5 We hypothesized that the April 20 cannabis celebration might be associated with a population-level increase in the risk of fatal traffic crash involvement.

Methods

This study used publicly available statistical data with a waiver of approval from the University of British Columbia research ethics board. We obtained fatal motor vehicle crash data from the United States National Highway Traffic Safety Administration’s Fatality Analysis Reporting System (FARS). FARS includes data on all crashes involving a motor vehicle traveling on public roadways in which at least 1 participant died within 30 days of the event. The study interval began the first full year after popularization of 4/20 in High Times magazine and extended to include the most recent year with data available, thereby reflecting 25 consecutive years (January 1992 to December 2016).

The primary analysis compared the number of drivers involved in fatal traffic crashes between 4:20 pm and 11:59 pm on April 20 each year to the number in fatal traffic crashes during the same time intervals on control days 1 week earlier and 1 week later (ie, April 13 and April 27). This design controlled for weekday, season, and year while minimizing bias from changes in vehicle design, travel distances, medical care and other confounders. We tested for differences between case and control dates using exact binomial tests and performed prespecified stratified analyses to examine individual factors and geographic variation.

Results

The 25-year study interval identified 1.3 million drivers involved in 882 483 crashes causing 978 328 fatalities. In total, 1369 drivers were involved in fatal crashes after 4:20 pm on April 20 whereas 2453 drivers were in fatal crashes on control days during the same time intervals (corresponding to 7.1 and 6.4 drivers in fatal crashes per hour, respectively). The risk of a fatal crash was significantly higher on April 20 (relative risk, 1.12; 95% CI, 1.05-1.19; P = .001).

Subgroup analysis suggested the relative risk increase on April 20 was particularly pronounced for younger drivers (Figure 1). No subgroup suggested April 20 conferred a contrary protective effect. Geographic analysis suggested the absolute risk increases were greatest in New York (excess of 36), Texas (excess of 32), and Georgia (excess of 29). Relative risk was significantly reduced only for Minnesota (Figure 2). Sensitivity analyses supported the results of the primary analysis, including evaluations of all crash-involved persons (rather than only drivers) and extended time intervals (4:20 pm to 5:00 am the following day). As expected, the number of drivers involved in crashes earlier than 4:20 pm or on nearby dates (April 18 and April 22) was no different than corresponding controls.

Discussion

We examined a quarter-century of national data and found a 12% increase in the relative risk of a fatal traffic crash after 4:20 pm on April 20 compared with identical time intervals on control days. Although the vast majority of Americans do not celebrate 4/20, the observed association was comparable in magnitude to the increase in traffic risks observed on Superbowl Sunday.6 Policy makers may wish to consider these risks when liberalizing marijuana laws, paying particular attention to regulatory and enforcement strategies to curtail drugged driving.

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Article Information

Corresponding Author: John A. Staples, MD, MPH, St Paul’s Hospital, 1081 Burrard St, Burrard Bldg, Rm 5910, Vancouver, BC V6Z 1Y6, Canada (jstaples1@providencehealth.bc.ca).

Accepted for Publication: December 2, 2017.

Published Online: February 12, 2018. doi:10.1001/jamainternmed.2017.8298

Author Contributions: Dr Staples had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: All authors.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: All authors.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: All authors.

Administrative, technical, or material support: All authors.

Study supervision: Redelmeier.

Conflict of Interest Disclosures: None reported.

Funding/Support:This work was supported by the Vancouver Coastal Health Research Institute, the Canadian Institutes of Health Research, and the Canada Research Chair in Medical Decision Science.

Role of the Funder/Sponsor: The funders/sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: We thank Clinton Pecenka, MPP, PhD, and Mark Staples, PhD, (Massachusetts Institute of Technology, Cambridge) for insightful comments on an earlier draft of this work. No compensation was provided for their contributions.

References
1.
Burke  K. Marijuana sales on 4/20 hit record highs. MarketWatch. June 14, 2016. http://www.marketwatch.com/story/marijuana-sales-on-420-hit-record-highs-2016-06-14. Accessed September 14, 2017.
2.
Bravo  AJ, Pearson  MR, Conner  BT, Parnes  JE.  Is 4/20 an event-specific marijuana holiday? a daily diary investigation of marijuana use and consequences among college students.  J Stud Alcohol Drugs. 2017;78(1):134-139.PubMedGoogle ScholarCrossref
3.
Record crowds of 80,000 descend upon Denver to mark historic 4/20 celebration of marijuana becoming legal in Colorado. Mail Online. April 20, 2014. http://www.dailymail.co.uk/news/article-2608727/Record-crowds-80-000-descend-Denver-mark-historic-4-20-celebration-marijuana-legal-Colorado-against-law-smoke-public.html. August 9, 2017.
4.
Hartman  RL, Brown  TL, Milavetz  G,  et al.  Cannabis effects on driving lateral control with and without alcohol.  Drug Alcohol Depend. 2015;154:25-37.PubMedGoogle ScholarCrossref
5.
Whitehill  JM, Rivara  FP, Moreno  MA.  Marijuana-using drivers, alcohol-using drivers, and their passengers: prevalence and risk factors among underage college students.  JAMA Pediatr. 2014;168(7):618-624.PubMedGoogle ScholarCrossref
6.
Redelmeier  DA, Stewart  CL.  Driving fatalities on Super Bowl Sunday.  N Engl J Med. 2003;348(4):368-369.PubMedGoogle ScholarCrossref
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