A radio telephone system has a plurality of base stations (3, 4) and a plurality of mobile radios. The position of the mobile radios are determined by combining information at the base stations (3, 4) with information from additional position indicators, such as beacons (16a, 16b, 16c) placed at intervals alongside a railway track (8). This enhanced information on the positions of the mobile radios enables channels to be reused on mobile radios with less physical separation than hitherto, thereby improving the efficiency of channel allocation.