Overview

• Senat and BVG have confirmed that neither existing nor autumn 2025 U-Bahn trains will be equipped with air conditioning due to tight tunnel clearances.
• More than 80 percent of Berlin’s U-Bahn tunnels date back over a century and leave only a few centimeters between train roofs and tunnel ceilings, making retrofits impossible.
• Officials warn that heat expelled by air-conditioning systems would exacerbate temperatures in confined tunnels and risk operational safety.
• Discussions with train manufacturers failed to yield a viable design for fitting air conditioning into the constrained tunnel environment.
• Starting in September 2025, 140 new cars will enter service on lines U1 to U4 and 346 cars will follow on U5 to U9 from autumn 2026 as part of a fleet renewal retiring all 1980s and early 1990s trains by the early 2030s.