Train speed is limited by a complex interplay of infrastructure, physics, and regulatory safety systems. The primary physical limit is the track geometry; tight curves require slower speeds to prevent derailment due to centrifugal force, though "tilting trains" can mitigate this slightly. The track quality (the weight of the rails and the stability of the ballast) also dictates the maximum safe velocity. Beyond physics, the signaling system is a major constraint; older systems rely on visual blocks that require long braking distances, whereas modern "ETCS Level 2" or Maglev systems allow for higher speeds by communicating directly with the train's computer. Power supply is another factor, as high-speed electric trains require massive amounts of voltage from overhead lines. Finally, environmental factors like noise pollution regulations near urban areas and the risk of wildlife or vehicle incursions at "level crossings" force trains to slow down. In 2026, many high-speed lines are "dedicated," meaning they have no crossings and very gradual curves to maximize the 300+ km/h potential of modern rolling stock.