Anyone who’s taken a summer subway ride in a major city already knows that stepping inside feels like you’re standing at the gates of hell. It feels like it’s suddenly become several degrees hotter, many percentages more humid, and you just know that your commute is going to be miserable. If you’ve been doing it long enough, you’ve probably noticed it’s only gotten worse, and you’ve probably complained about it on some social media platform or another.

Researchers combed the Internet to compile a master list of thousands of subway commuters’ complaints about excessive heat, concluding that you’re the only one feeling it. It’s a sentiment shared by many and backed up by science.

A study published in Nature Cities analyzed more than 85,000 online comments posted by riders in New York, Boston, and London between 2008 and 2024. Researchers from Northwestern University combed through social media posts and Google reviews for heat-related complaints containing words like “hot,” “boiling,” or “scorching.”

After filtering out irrelevant phrases that would just muddy the findings (unfortunately, while a subway hotdog might be delicious, it did not count), they identified more than 22,000 genuine complaints about uncomfortable subway temperatures.

Subways Are Dangerously Hot, and They’re Only Getting Worse

The researchers were able to establish a clear pattern of temperatures rising above ground, generating a series of underground complaints about heat. For every 1-degree Celsius increase above about 10°C (50°F), complaints increased by roughly 10 percent in Boston, 12 percent in New York, and a wild 27 percent in London, a city notorious for not being able to stand a little heat.

The reason for the subway sweltering lies in simple physics and urban design. Underground tunnels are surrounded by soil and rock that trap heat rather than let it dissipate. All the individual elements that make up the classic subway atmosphere—the squeak of braking trains, electrical equipment, harsh lighting systems, and the thousands of human bodies shuffling in and out—all add to this subterranean oven that can meet or exceed surface temperatures.

Those Londoners complaining about how hot it is when temperatures rise may be onto something, as the London Underground has recorded temperatures as high as 47 degrees Celsius (116 degrees Fahrenheit). That is hotter than the city’s highest recorded air temperature above ground.

The complaints generally follow daily routines. Complaints spiked and London’s afternoon hours peaking around midday and again in the evening in Boston and New York. They dropped off over the weekend when the trains weren’t as packed, and commuters weren’t draped in hot and heavy work clothes.

Extreme heat is one of the deadliest climate-related hazards worldwide, and underground environments like subways can amplify it, often to dangerous extremes that not only pose a direct threat to people but also warp rails and accelerate the aging of transit equipment. Monitoring these complaint patterns in real time could help transit agencies respond more effectively by running cooling systems or venting at specific times of day.