Association of nighttime heat with road traffic mortality: A time-stratified case-crossover study

• Daily minimum temperature is examined as a new metric for its association with road mortality. • Risk of nighttime road mortality rises with nocturnal heat exposure. • Females are more at risk of nighttime road mortality from temperature extremes than males. • Young adults aged 21–40 face higher risk of nighttime road mortality from heat. • Young (0–21) and elderly (65+) are more at risk of nighttime road mortality from heat and cold. Road traffic incidents pose public health concerns worldwide, particularly during nighttime driving when incidents frequently result in fatalities. These risks are further exacerbated by the effects of global warming, which have heightened awareness of the increased vulnerability to nighttime heat exposure, particularly in densely populated urban areas. Despite previous research emphasizing the heightened risk of road crashes in hot conditions, there remains a significant gap in addressing nighttime scenarios. This study aims to bridge this gap by investigating the relationship between nighttime temperatures and road mortality. Utilizing road mortality records and temperature data from the Taipei metropolitan area, Taiwan, the study employed a time-stratified case-crossover design. Leveraging a distributed lag non-linear model with a conditional quasi-Poisson model, it pioneers the use of daily minimum temperature as a temperature metric. The findings underscore a more pronounced association between temperature and road mortality at night compared to daytime. Moreover, sex- and age-stratified analyses reveal higher vulnerability to nocturnal heat-induced road mortality among females and young adults (21–40 years). To mitigate temperature-induced nighttime road safety risks, policymakers are urged to implement demographic-targeted interventions. This study carries broad implications globally, particularly considering the narrowing diel temperature range attributed to urban heat island effects amid ongoing global warming and rapid urbanization.