“While tunnels are probably the most obvious obstacle to achieving line of sight, mobile signals are also blocked by mountains, trees, buildings, etc.,” says Val. Even the train itself can block mobile signals, because they are essentially big metal tubes traveling at incredibly high speeds.

Phone signal on trains is notoriously poor due to a combination of High-Speed Handover and the "Faraday Cage" effect. As a train moves at 100+ mph, your phone must constantly "hand off" its connection from one cell tower to the next; if the handoff isn't perfect, the call drops or data stalls. Additionally, modern train cars are constructed with thick metal shells and windows coated with a metallic film to reduce solar heat and improve air conditioning efficiency. This film effectively shields the interior, blocking the radio waves your phone needs to communicate with towers outside. In 2026, many rail networks are mitigating this by installing "on-train repeaters" or high-speed Wi-Fi, but in rural "dead zones" where tracks often run through deep cuttings or tunnels, even the best technology struggles to penetrate solid rock. A grounded "pro-tip": sit near a door or use the train's Wi-Fi for calling to bypass the metal shielding of the carriage.