Alberta Highway 4

A Highway 4 bypass of the town of Milk River was completed in 2009, the final section of the highway to become divided

Like many other main highways in southern Alberta, the alignment of Highway 4 is based on an existing railway.[13] In the late 1890s, a railway was constructed between Lethbridge and Coutts by the Alberta Railway and Coal Company, who then extended the route to Great Falls, Montana.[14] A spur to the southwest from Stirling to Cardston was also built. A trail developed paralleling the railroad, eventually evolving by 1912 into a dirt road known as part of the Sunshine Trail.[15][16] The route was identified as a key corridor connecting Alberta to major cities of the United States for the purposes of trade and tourist travel.[17] Lethbridge mayor W. D. L. Hardie supported proposals for the road to be gravelled, claiming it would be a relatively easy and affordable process and could set precedent for other gravelling projects in the province.[18] In tandem with the Red Trail (now Highway 3) and Highway 1 (now Highway 2), Highway 4 comprised the north portion of the all-weather Sunshine Trail that would eventually run from Los Angeles to Peace River.[19][20]

The alignment of the highway has changed slightly from its inception to the present day. From its northern end in Lethbridge, it originally followed the railway line on a southeasterly heading before turning due east along Township Road 54 at New Dayton.[9] It then followed present-day Highway 36 south through Warner, before turning back east toward the railway north of Milk River, before following it through the town and into Coutts.[9] In 1938, Lethbridge City council lobbied to the provincial government for the entire route to paved.[21] Along with other Lethbridge officials, they hoped the highway would be given priority over other projects in the area as the Coutts border crossing was far and away the busiest in Alberta, carrying more traffic than all the others combined.[22] Work began in 1945 to reconstruct and straighten out the existing alignment of the highway that consisted of the numerous aforementioned 90° turns.[23] The first section to be reconstructed and paved was from Coutts to Craddock.[24] Work continued on the northern half of the highway and was mostly completed by 1947, with the official opening of the new Lethbridge–Coutts highway held in May 1948 in Coutts. [25][26] The road was designated as Highway 4 by the following decade.[15][27]

43 Street in south Lethbridge, the busiest section of Highway 4

Prior to the construction of 43 Street, the former alignment of Highway 4 in Lethbridge was along Mayor Magrath Drive, cosigned with Highway 5 to 3 Avenue in south Lethbridge, which was then Highway 3.[28] It was later signed as 24 Avenue past Highway 5 (Mayor Magrath Drive), becoming Scenic Drive and continuing in a northwest direction to Highway 3 near downtown.[29] In 1992, 43 Street in south Lethbridge was widened from two to four lanes, although it did not carry the Highway 4 designation at this time.[30] Ordinarily, Alberta begins to consider upgrading to a divided highway when traffic levels reach 10,000 vehicles per day.[31] The majority of Highway 4 remains well below this threshold, but it is a component of the CANAMEX Corridor in southern Alberta, to which Alberta had made a commitment to upgrading in the late 1980s. Plans for a divided highway were confirmed by 1989, and reiterated as a priority by annual reports published by Alberta Transportation through the 1990s. The highway was the southernmost component of what was then called the Export Highway, which also included Highways 2 and 3, which were given priority for twinning in the first half of the 1990s.[32][33] In 1993, federal and provincial funding was announced for various twinning projects in Alberta, including the entirety of Highway 4.[34]

By 1996, work had begun on a 13 km (8.1 mi) section north of Coutts, and a $26 million commitment had been made by Alberta to a group of projects that included the widening of Highway 4 in Lethbridge.[35][36] By 1998, a 12 km (7.5 mi) section south of Lethbridge to Highway 845 had been completed.[37] For the majority of the highway, the newly constructed lanes carried northbound traffic and the existing road was converted to carry southbound traffic.[38] Almost all work had been completed before the end of the decade.[39] On September 18, 1999, Highway 4 was renamed the First Special Service Force Memorial Highway.[40][41] The route was travelled between 1942 and 1944 by Canadian volunteers of the force to join their American counterparts for training at Fort William Henry Harrison near Helena in preparation for World War II.[42][43] Several Canadian and American members of the force that came to be known as the "Devil's Brigade" were on hand in Milk River for the dedication of plaques for the route, and signs at both ends of the highway were erected.[43] Interstate 15 between Sweet Grass and Helena had received the same name in 1996.[40]

The section of Highway 4 through Milk River was the last remaining section that was not a divided expressway. Work had been delayed by land acquisition and some uncertainty on the final routing.[39] A bypass east of the town and upgrades to the existing route through the community had been considered, but ultimately a new twinned highway west of the town, and a relocation of the railway, was chosen.[39] The $59 million project included the construction of two bridges over Milk River and was completed in 2009.[44]