In the summer, NYC Subway platforms can reach temperatures exceeding 100°F (38°C), even when it is only in the low 90s at street level. This "furnace effect" is caused by the lack of ventilation and the massive amount of heat generated by the train engines and air conditioning units on the cars themselves, which exhaust hot air onto the platforms. Some stations, like Union Square or Times Square, are notorious for being 10–15 degrees hotter than the outside air. While the train cars themselves are air-conditioned and typically stay around 72-76°F, the wait on the platform can be a genuine health risk for vulnerable individuals during July and August heatwaves.