Abstract
Modern public transport networks need a modern digital communications network. The requirements for such a system are outlined. The creation of the Terrestrial Trunked Radio (TETRA) standard defined by the European Telecommunications Standardisation Institute (ETSI) and the resulting multi-vendor business system with almost 20 independent ratio suppliers producing compatible equipment is described. TETRA is used in underground railways, tram and bus services, railways, airports and harbours in many cities. TETRA features group call, calling by functional numbers and voice coding, wide area coverage, dispatch flexibility and pre-emptive emergency calls. Details are given of the TETRA technology and equipment.