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. 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. 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. Ordinarily, Alberta begins to consider upgrading to a divided highway when traffic levels reach 10,000 vehicles per day. 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. In 1993, federal and provincial funding was announced for various twinning projects in Alberta, including the entirety of Highway 4.