Effects of urbanisation and seasons on the relationship between frozen road conditions and road traffic injury: a longitudinal study of national emergency medical service data in South Korea.

Background: Frozen road conditions could be a factor in road traffic injuries, and seasonality and urbanisation level are potential influencing factors. However, few studies have considered this relationship. Therefore, we examined the effect of frozen road conditions on road traffic injury rates and the differences across seasons and urbanisation levels.

Methods: We used nationwide data on road traffic injuries and weather from the National Emergency Medical Service Run Sheet and the Korea Meteorological Administration, respectively, from 2018 to 2021. We analysed the relationship between frozen road conditions and road traffic injuries by administrative district and day using a generalised estimating equation with log link function and Poisson distribution, stratified by season and urbanisation level.

Results: After excluding summer, the analysis of 605 254 road traffic injury cases revealed a higher road crash incidence under frozen road conditions, with injuries increasing by 30% (rate ratio (RR): 1.33, 95% CI: 1.30 to 1.37). The relationship between road traffic injury rate and frozen road conditions varied significantly by season and urbanisation level. The stratification analysis showed that the relationship between these two variables was significant in the fall (RR: 2.07, 95% CI: 1.74 to 2.46) and winter (RR: 1.37, 95% CI: 1.34 to 1.40). Furthermore, the road traffic injury rate was higher on frozen road conditions in urban (RR: 1.24, 95% CI: 1.19 to 1.29) and rural areas (RR: 1.47, 95% CI: 1.42 to 1.51), not in metropolitan areas.

Conclusion: The road traffic injury rate increased under frozen road conditions and varied by season and urbanisation level. These findings indicate the need for road safety strategies tailored according to season and urbanisation level.