Assessing the Effects of COVID-19 Policies on Traffic Accident Casualty Rate in Chicago: A Controlled Interrupted Time Series Analysis

This study used a controlled interruption time series to analyze the impact of Chica-go's COVID-19 policies on traffic safety, including stay-home orders, cautious reopening, gradual return, second wave of restrictions, restrictions lifed, and the new normal. The heterogeneity of policy effects among different population groups is also consid-ered. The results showed that: 1) Stay-at-home order and cautious opening policy had adverse effects on the casualty rate, and the effect of cautious opening policy was more significant;The stay-at-home order led to a spike in injury rates only in the first few weeks, while the rate continued to rise during the cautious reopening, suggesting that the policy could have long-term adverse effects. 2) The reduction in mortality rates under the new normal phase was the most significant among all the reopening stages, and by the end of 2021, overall mortality rates returned to levels seen in previous years. 3) Males faced higher risks during lockdowns and initial reopening, whereas females experi-enced increased casualties during commercial or entertainment venue reopenings. 4) Casualty rates for cyclists and pedestrians were less affected by the blockade and initial reopening. However, pedestrian casualty rates increased during the reopening phase, especially after the reopening of the recreational and commercial sectors. 5) Young people had lower casualty rates during the reopening phase, but their rise was more pronounced during the lockdown. In terms of casualty rate, the elderly are less sensi-tive to policy interventions. These findings highlight the need to consider phased changes in travel patterns and demographic differences when formulating traffic management strategies at different stages of a pandemic.