Shinkansen routes are completely separate from conventional rail lines (except Mini-shinkansen which goes through to conventional lines). Consequently, the shinkansen is not affected by slower local or freight trains, and has the capacity to operate many high-speed trains punctually. The lines have been built without road crossings at grade . Tracks are strictly off-limits with penalties against trespassing strictly regulated by law. It uses tunnels and viaducts to go through and over obstacles rather than around them, with a minimum curve radius of 4,000 meters (2,500 meters on the oldest Tōkaidō Shinkansen).