Effects of hourly precipitation and temperature on road traffic casualties in Shenzhen, China (2010-2016): A time-stratified case-crossover study

Background: Although road traffic casualty (RTC) is preventable, it remains the eighth leading cause of death globally, especially in developing countries. Previous studies suggested the association between RTC and monthly or daily weather conditions, while the acute effects of weather conditions on an hourly timescale remains unknown. This study aims to quantify hourly effects of precipitation and temperature on RTC. Methods: Using ambulance records on RTC during 2010-2016 for the whole population in Shenzhen, China, we conducted a time-stratified case-crossover design which can inherently control for hour of the day, day of the week, seasonality, time trends and potential time-invariant confounders. Conditional quasi-Poisson regression with distributed lag nonlinear model was used to determine the effects of hourly precipitation and temperature on RTC. Results: Light and heavy precipitation increased RTC in current and following 2 h by 8.09% (95% CI: 4.20-12.12%) and 11.62% (95% CI: 5.93-17.62%), respectively. A J-shaped temperature-RTC curve revealed that each 1 degrees C increment above 17 degrees C were associated with a 0.87% (0.52-1.22%) increase in RTC. High temperature accounted for 6.44% (95% CI: 3.95-8.91%) of all RTC, with a high fraction of 10.64% (95% CI: 4.33-15.96%) during warm season and 8.30% (95% CI: 4.26-12.66%) in traffic peak hours. Precipitation contributed to 0.68% (95% CI: 0.44-0.92%) of RTC within 3 h. The middle-aged and female suffered more from precipitation-associated RTC, and the younger suffered more from high temperature-associated RTC. Conclusions: High temperature increased substantially hourly RTC. Precipitation was also a risk factor of RTC and the adverse effect lasted for 3 h. The findings would be helpful to guide the development of targeted intervention to accelerate progress in road traffic safety. (C) 2020 Elsevier B.V. All rights reserved.