With its central position in Europe, Germany is a transport hub for the continent. Its road network is among the densest in Europe. The motorway (Autobahn) is widely known for having no federally mandated speed limit for some classes of vehicles. The InterCityExpress or ''ICE'' train network serves major German cities as well as destinations in neighbouring countries with speeds up to . The largest German airports are Frankfurt Airport and Munich Airport. The Port of Hamburg is one of the top twenty largest container ports in the world.