The invention concerns a method of determining traffic data from vehicles which are each equipped with at least one decentralized unit having at least one mobile communication function and a function for obtaining time information as well as a storage facility. At least one central unit with control and processing functions is associated with a plurality of decentralized units. During travel, the decentralized unit receives and evaluates data characterizing the cells, and other radio and transmission data. Data characterizing a change of cell are recorded together with time marks.