In March 2019 researchers from the UK and the USA published the results of their study to assess whether there is an increase in UK road traffic accidents on cannabis celebration day which is held on 20 April at 4.20 pm, also known as “420 day”. Information on UK car accidents resulting in death or injury was collected from 51 local police forces covering the period 2011-2015. A comparison was then made between the number of car accidents occurring from 4.20 pm onwards on April 20 and the number of car accidents occurring during the same time period on the same day of the week in the preceding and succeeding two weeks. Results showed that on average there was an additional 23 police-reported car accidents on cannabis celebration day compared to other days, which corresponded to an 18% increase in the risk of collision.
Vandoros S, Kawachi I. The relative risk of motor vehicle collision on cannabis celebration day in Great Britain. Accid Anal Prev. 2019 Mar 8. [Epub ahead of print]