In this area (from about half a mile east of junction 5 to two miles west of it) the M8 is essentially an online upgrade of the previous A8, which was a 1930s new build (see A8/History).
The first section of the M8 to open was the Harthill bypass in November 1964. Its original west end was a temporary tie-in about 0.6 miles east of junction 5. The motorway was extended the short distance to junction 5 in November or December 1965. As the motorway was on the same line as the A8, the whole junction was opened at this time. The extension of the M8 westward to the next junction was in August 1967.