Traffic fatality rates are around 9% higher on hot days compared to mild-temperature days.

Heat can impair driver judgment, slow reaction times, and increase speeding and aggressive driving.

Risk extends to pedestrians and cyclists, who are also affected by heat and less protected.

Over 1 million people die in traffic accidents every year. According to the WHO Global Status Report on Road Safety 2023, the figure was 1.19 million in 2021 alone. The numbers have been declining in recent years, reflecting improvements in road and vehicle safety. But the human toll remains unacceptably high. As of 2019, road traffic crashes were still the leading cause of death among children and young people between 5 and 29 years of age, and the 12th leading cause of death overall.

No matter how much road and vehicle safety improve, the human factor will always be harder to control. And there are reasons to think that this particular dimension may be getting worse.

The reason is the increase in extreme heat events around the world.

In recent posts, we discussed how heat clouds people's thinking, resulting in poor decisions, and lowers impulse control, resulting in more violent crime. Put those two facts together, and the implications for driving become clear. When judgment is impaired and impulses take over, the consequences behind the wheel can be severe.

Sometimes, phrases like "impaired judgment" or "impulsive decision-making" sound too abstract. Consider what they look like in traffic: speeding; turning without signaling; impatient overtaking; ignoring blind spots; road rage; reversing without checking; tailgating; jaywalking. Less abstract now?

Driving Under the Influence of Heat

The effects of extreme heat on driving have been known for decades. Research from the 1970s and 1980s........

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