Individual and city-level variations in heat-related road traffic deaths in Latin America.

Latin America experiences both high road traffic mortality and extreme heat, which have been shown elsewhere to be interrelated. However, few studies have examined this association in Latin America-one of the world's most urbanized, fastest-motorizing region, with a high share of vulnerable road users-and even fewer have analyzed multiple cities across diverse climates and urban settings. Leveraging ambient temperature and road traffic mortality data (2000-2019) from 272 cities in six Latin American countries, we conducted a time-stratified case-crossover study. Based on over 1.9 million city-days of data, we found that road traffic mortality risk generally increased with temperature in a monotonic pattern, with significantly elevated risks on extremely hot days, defined at the 95th and 99th temperature percentiles. Risks were particularly high among younger individuals (≤19 years), males, motorcyclists, bicyclists, and in cities with hotter climates, longer commutes, and more extended street segments. Cities in the tropical Global South should prioritize protecting vulnerable road users, particularly those in peripheral areas, where many endure long, heat-exposed commutes in informal, non-climate-controlled transport.