Word Origin & History
c.1500, "trade, commerce," from M.Fr. trafique (1441), from It. traffico (1323), from trafficare "carry on trade," of uncertain origin, perhaps from a V.L. *transfricare "to rub across" (from L. trans- "across" + fricare "to rub"), with the original sense of the It. verb being "touch repeatedly, handle."
Or the second element may be an unexplained alteration of L. facere "to make, do." Klein suggests ultimate derivation of the Italian word from Arabic tafriq "distribution." Meaning "people and vehicles coming and going" first recorded 1825. The verb is from 1540s (and preserves the original commercial sense). Traffic jam is 1917, ousting earlier traffic block (1895).