Parked cars can turn deadly traps, cabin temperatures touch 64.9°C: Study

The research, published in the Journal of Environmental Management, involved real-time monitoring of thermal comfort and air quality inside three types of cars—sports utility vehicles (SUVs), hatchbacks, and sedans—parked during Chandigarh’s summer to assess the heat-health risks faced by occupants.

Temperature, relative humidity, carbon dioxide, and carbon monoxide levels were measured inside completely closed vehicles to assess thermal comfort. Cabin temperatures ranged from 26.7°C to 64.9°C, while humidity varied from 8.3 per cent to 60.4 per cent.

While speaking to The Indian Express, Dr Ravindra Khaiwal said, “Extreme heat inside parked vehicles is an emerging but under-recognised public health risk. Climate-resilient policies, heat-warning technologies in vehicles, improved car design, and better urban planning are essential to prevent heat-related illnesses and save lives in a warming world.”

Black sedan worst performer

An interesting finding was that a black sedan consistently recorded higher cabin temperatures than a white SUV and a hatchback, indicating that vehicle colour can significantly influence heat absorption and occupant comfort during summer.

Researchers found that the front cabin consistently recorded higher temperatures than the rear and black sedans recorded the highest temperatures and poorest thermal comfort. The study stated that black absorbs more heat than white vehicles. It also observed that temperatures were often higher in the evening than in the afternoon because the vehicles continued to absorb heat throughout the day and did not cool down despite falling ambient temperatures.

Using internationally accepted thermal comfort indices—predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD)—the researchers concluded that every vehicle tested fell into the “hot” category, with 100 per cent predicted occupant dissatisfaction.

Even people standing outside in the summer heat experienced poor thermal comfort, but conditions significantly worsened immediately after entering a parked vehicle. PMV values inside the cars were far beyond acceptable limits, particularly in sedans.

The study warned that exposure to such extreme cabin temperatures can trigger heat stress, heat exhaustion, heat stroke, blood pressure fluctuations, and reduced concentration, increasing the risk of accidents. It also cautioned against immediately switching on the air-conditioner after entering an overheated vehicle, saying sudden exposure to blasts of cold air after intense heat may also adversely affect health.

Besides heat, researchers also monitored in-cabin air quality.

Carbon monoxide concentration increases

Carbon monoxide concentrations in some cases exceeded the most stringent indoor air quality limits, although carbon dioxide levels remained within permissible limits. The study noted that heat stress and air pollution together can amplify health risks for occupants.

As part of nature-based solutions, researchers suggested promoting tree-lined roads, shaded parking lots and green parking infrastructure, which can significantly lower surface and ambient temperatures around vehicles.

The study suggested increasing urban green cover, using pergolas with climbing plants, and integrating green spaces into parking areas can reduce direct solar exposure, making vehicles safer and more comfortable while also helping cities adapt to rising temperatures caused by climate change.

AI thermal comfort sensors and safer vehicle design

Also, to reduce the risks, the study recommended the development of AI-enabled thermal comfort sensors capable of warning occupants through colour-coded alerts before they enter an overheated vehicle. It also urged automobile manufacturers to incorporate thermal comfort into vehicle design by considering factors such as vehicle colour, cabin materials and ventilation.

Practical measures such as roof ventilation fans, partially opening windows, and using sunshades can significantly lower cabin temperatures and improve occupant safety, the study said.

The researchers concluded that as climate change drives more frequent and intense heatwaves, vehicle cabins will increasingly act as hazardous closed microenvironments. They stressed the need for larger studies across different climates and seasons to develop evidence-based policies and safer vehicle designs for tropical countries like India.

The study found that after cabin temperatures exceeded 40°C, they took significant time to cool to acceptable levels.

Researchers noted that since most people enter their vehicles immediately and start driving, they remain exposed to severe heat stress during the initial minutes of the journey.

Researchers cautioned that the findings have serious implications for children, the elderly and people with cardiovascular illnesses, who are more susceptible to heat stress. They warned that extremely high cabin temperatures can quickly become life-threatening, particularly if occupants remain inside a parked vehicle.

Beyond health concerns, the researchers warned that excessive heat can impair concentration, reduce sensory-motor performance, and slow reaction times, increasing the risk of road accidents, especially immediately after entering an overheated vehicle.

Key findings

Maximum cabin temperature: 64.9°C

Maximum predicted occupant dissatisfaction: 100%

Front seats hotter than rear seats.

Black sedans recorded the worst thermal comfort.

Evening cabin temperatures were often higher than afternoon temperatures.