Not entirely true since the 1990s when JR East introduced two 'Mini Shinkansen' branches on former narrow gauge routes that had been converted to standard gauge. Like our UK classic compatibles, the high speed trains that use these are specially constructed with restricted body profiles to fit through structures too small for other 'captive' Shinkansen trains that stay wholly on the high speed network. On the branches concerned, other local stopping services also run using standard gauge variants of typical Japanese low speed emus and there are areas of dual gauge track traversed en route as well. The platform height is very similar on both Shinkansen and metre gauge networks although on high speed lines the edge is set back from the rail a little further so the special trains need extending gap filler steps at doors that deploy at stations on the HS line, as planned in UK. So it is no longer true to say that the Shinkansen network is WHOLLY segregated from other rail traffic in Japan. Hokkaido Shinkansen expresses also share dual gauge track with freight through the undersea Seikan Tunnel.