Helsinki Metro in Finland is the world's northernmost metro system. They use professional communications to ensure smooth passage for their 90 million passengers per year.
Régie Autonome des Transport Parisiens (RATP), is the transportation company for the urban areas of Paris, France. The company uses a Airbus TETRA system for their communications over the whole area.
Shenzhen Metro has used TETRA communication since 2004 in line #1. Shenzhen is the first city in China that interconnect TETRA systems between different metro companies and their metro lines.