Objective To describe temperature change throughout the workday in an enclosed vehicle in Austin, Texas across the calendar year while accounting for heat index.

Methods In this observational study, vehicular temperature was measured 1 day per month during 2012 in Austin, Texas. Data were recorded at 5-min intervals via an EL-USB-1-PRO digital temperature sensor from 8:00 to 16:00. Selected days were primarily cloud-free (with ‘clear’ or ‘few clouds’) with a predicted ambient temperature high within ±20°F of the 30-year normal high. Referent temperature and 30-year normal data were collected via the nearest National Weather Service (NWS) weather station. The NWS heat index and corresponding hazard levels were used as a guideline for this study.

Results Per NWS guidelines, the enclosed vehicle temperature rose to ‘danger’ levels of ≥105°F (41°C) in all months except January and December and to ‘extreme caution’ levels of ≥90°F (32°C) in every month of the year. In June, the vehicle rose to ≥105°F (41°C) by 9:25. The hottest vehicular temperature achieved was 137°F (58°C). In 9 months of the year, the vehicle reached ≥90°F (32°C) by noon. We also found that an ambient temperature as low as 68°F was associated with vehicular temperatures ≥105°F (41°C).

Conclusions Infants and children in states that experience mild winter temperatures face the threat of vehicular hyperthermia disability and death across the calendar year. Prevention efforts that focus on awareness of a childhood heat vulnerability, parental perception of susceptibility to forgetting a child in a vehicle and universal availability of vehicular safety devices may reduce paediatric vehicular hyperthermia death.