Automobile communications method and system

An automobile communication system which can ensure fast hand-over without putting unnecessary burden on mobile stations and can adequately handle changes in road condition is disclosed. For each of the radio zones (RZ1-RZ5) formed by roadside transceivers (TRX1-TRX5) arranged along a road (10), a plurality of transmission and reception frequencies ft1/fr1 and ft2/fr2 are provided. The in-use transmission/reception frequencies in adjoining radio zones are switched at predetermined timing such that they are not permitted to be overlapped. By switching a time slot allocated to the vehicle-mounted transceiver, the vehicle-mounted transceiver can continuously communicate with the roadside transceivers at the same communication frequency over the radio zones.