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The problems of using existing automatic vehicle identification (AVI) systems for detection of vehicles on the busy city roads arise because physical barriers between lanes in the city toll sites are not desirable, while the traffic does not always comply with the lane disciplines. A new AVI system is described in this paper using the randomised time division multiplexing (TDM) technique for detecting several vehicles simultaneously entering the detection zone. Laboratory experiments carried out for up to 8 identification tags at the same time showed that all replies were detected for 900 interrogations. The collision of replying signals did not occur. The high speed transmission of serial data has, however, an error rate of 3 % - 7 %. Under the laboratory conditions, the detection errors were eliminated simply by allowing the tags to reply twice.