The 1923 state route between Bell Station and Pacheco Pass had numerous curves and steep grades. In 1939, a realignment of 2.6 miles of highway was completed eastward from the Pacheco Reservoir area (starting about a mile east of Bell Station). In 1950, the first four-lane expressway segment was constructed from the 1939 alignment to near the Merced County line, a distance of 3.26 miles. The 1939 and 1950 alignments continue to be in use today.