Assessment of Traffic Accidents in Japan during the COVID-19 Pandemic vs. Previous Years: A Preliminary Report.

Beginning in April 2020, social distancing measures were implemented to mitigate the COVID-19 pandemic in Japan. We assessed whether traffic accident rates had decreased from April 2020 to December 2021 as compared with previous years. The analysis included 2,934,477 traffic accidents, and the trend of decreasing rates of traffic accidents in recent years and seasonal fluctuations in traffic accidents were considered. The yearly change in the traffic accident rate between 2015 and 2019 was estimated, and the traffic accident rate in 2020 and 2021 was predicted. This was followed by the comparison of observed vs. predicted traffic accident rate. In 2020, the observed vs. expected rates of traffic accidents were lower in April to December 2020, and the rate of traffic accidents in Japan was 30-40% lower in April-May 2020 than would be expected based on trends from previous years. In 2021, rates of traffic accidents remained lower than expected between January and November, but the magnitude of decrease was not as pronounced. These findings could be explained by social distancing policies, including the declaration of the state of emergency, and the relaxation of public health and social measures over time.