Route 342 is a provincial highway located in the Montérégie region of Quebec west of Montreal. It runs from the Ontario-Quebec border in Pointe-Fortune (at the junctions of Ontario Highway 417 and Autoroute 40 and ends in Vaudreuil-Dorion at the junction of Autoroute 20. Before the construction of Autoroute 40 in 1959 (and its continuation in Ontario as Highway 417) it was the main route between Montreal, Quebec and Ottawa, Ontario (becoming Route 17 in Ontario). It serves as an alternate route to Autoroute 40 and has 4 interchanges with it in Pointe-Fortune, Rigaud and Hudson.