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Every summer, Seoul's subway system becomes a battleground over air-conditioning complaints. Riders flood the system with grievances ranging from "It's too hot — turn the AC down further" to "The AC is blowing too hard," but cabin temperatures are not something train crews can adjust. Seoul Metro said, "Heating and cooling inside cabins is automatically regulated to a set temperature by individual temperature sensors," adding that it would "strengthen public information and outreach on how the heating and cooling system works."
According to Seoul Metro on the 24th, of roughly 1.01 million complaints filed last year, about 790,000 — or 78.4% of the total — concerned heating and cooling. Of those, some 749,000 were complaints that it was too hot. Such complaints have been rising as climate change intensifies summer heat waves. Heating and cooling complaints stood at about 446,000 in 2021, accounting for 58.7% of the total, before climbing to 570,000 (65.3%) in 2022, 880,000 (76.9%) in 2023, and 930,000 (80.6%) in 2024. Last year's figure of 798,000 (78.4%) was slightly lower than the previous year but remains high.
Under Ministry of Environment guidelines, train heating and cooling systems are set to 24–27 degrees Celsius in summer and 18–21 degrees in winter, operating automatically based on the target temperature. Even when passengers request "power cooling," train crews cannot adjust the temperature at will, the operator said.
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To raise awareness, Seoul Metro is extending heating and cooling notices — already posted on Lines 2 and 8 last year — to Line 6 as well. The operator's official "Ttota" app is also displaying notices warning that excessive heating and cooling complaints are hindering responses to urgent matters such as medical emergencies and crimes. With more than 70% of complaints filed through the Ttota app, the operator expects a meaningful reduction in complaint volume.
Beyond outreach, Seoul Metro is also rolling out measures to make rides more comfortable. Starting next week, it will pilot an "AI-based optimal cabin temperature control system" on one Line 4 train, with plans to expand to 25 trains. The system uses learned congestion-forecast data to allow AI to preemptively adjust cooling before a train enters a crowded section.
Seoul Metro recommends that passengers who feel hot move to the ends of the cabin. Due to airflow patterns inside the train, the middle of the cabin tends to be the warmest, while both ends are comparatively cooler. Passengers who feel cold, on the other hand, can use the weak-cooling cabins, which are kept about 1 degree warmer than regular cabins.
Ma Hae-geun, head of Seoul Metro's Operations Division, said, "Train heating and cooling is an automatically controlled system based on Ministry of Environment standards, and all departments are working together to create a comfortable riding environment." He added, "Since crews cannot adjust cooling at their discretion, we ask for citizens' understanding and cooperation so that urgent complaints such as medical emergencies and crimes can be handled first."
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