southern interchange with I-475 near Macon. It was open from I-16 to US 23/SR 42 near Forsyth. It was open from Forest Park to its northern interchange with I-285. In 1967, it was under construction from US 80/SR 74 to I-16 in Macon. It was under construction from near Forsyth to the US 19/US 41 interchange west of Morrow. It was open from Forest Park to SR 120 in Marietta. It was under construction from SR 120 to Allgood Road in Marietta. In 1968, the highway was open US 23/SR 42 near Forsyth to SR 20 in McDonough. It was under construction from McDonough to SR 54 in Morrow. It was open from Morrow to Allgood Road in Marietta. It was under construction from US 411/SR 61 near Cartersville to SR 140 in Adairsville. In 1969, the highway was under construction from its southern interchange with I-475 to I-16 in Macon. It was open from I-16 to Allgood Road in Marietta. 1970s In 1971, it was open from the Florida state line to Allgood Road in Marietta. In 1973, it was under construction from Marietta to SR 92 in Acworth. In 1974, the highway was under construction from Emerson to US 411/SR 61 near Cartersville. The last segment of I-75 in Georgia, located between Emerson and Cartersville, opened on December 21, 1977. 1980s Much of the work to widen interstates across Atlanta including I-75 from six to eight lanes and the Downtown Connector to 10 lanes including the elimination of sharp curves and grades, left-hand exits, excessive interchanges, and short acceleration/deceleration lanes, took place in the 1980s. Construction began with widening I-285 first, beginning in 1976, continued to the radiating expressways, and concluded with the depressed sections of the Downtown Connector which were completed in 1988. I-75 widening from I-285 and Aviation Boulevard to the Downtown Connector was completed by late 1984. I-75 widening from the Brookwood Interchange to the Chattahoochee River and Cobb County line was widened in the early 1980s and completed by 1985. Work on the Downtown Connector portion began in 1984, and included redesigning the massive interchange between I-20 and I-75/I-85 and the design and construction of 55 bridges over the connector portion alone. The project was completed in November 1988. After completion In addition to the general-purpose lanes added in the 1980s, provisions for high-occupancy vehicle lanes (HOV lanes) and dedicated onramps at Williams Street,