Highway 3 begins as a two-lane continuation of BC Highway 3 in the Canadian Rockies at Crowsnest Pass, winding through the foothills to a junction with Highway 2 west of Fort Macleod. Briefly concurrent with Highway 2, it becomes a divided highway and part of Alberta's Export Highway, a segment of the CANAMEX Corridor that stretches from Alaska to Mexico. In Lethbridge it is an expressway named Crowsnest Trail that crosses the Oldman River and meets the northern termini of Highways 4 and 5; the former is a major route that assumes the designation of the Export Highway, connecting to Interstate 15 in Montana, while the latter branches southwest to Magrath and Cardston. Leaving Lethbridge, Highway 3 passes through Coaldale and Taber before reverting to a two-lane highway that ends at Highway 1 in Medicine Hat.