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30.97 miles ; from I-75 north of Marietta (Atlanta) to GA 5 in Nelson. Construction started in 1979; opened in 1987. Provides access to the northern Georgia mountains, as well as far-flung rapidly growing Atlanta suburbs ("white flight", Jim K. Georges writes). 
I-575 is four lanes throughout; the southern 15 miles were built before the northern half, and drivers will notice the difference in bridge styles. There is talk of widening to 6 lanes near I-75, as well as completing the half-interchange there (no NB <-> SB access).
See also: I-575 (aaroads)