What are the Interstates between Indianapolis and Atlanta
From Indianapolis I-65 goes down to Nashville and then you would take I-24 Chattanooga and then I-64 to Atlanta That's the fastest and is 535 miles plus or minus. It is a little shorter (516 miles) but will take longer to take a non-interstate from north of Bowling Green (Kentucky) down to Chattanooga because I-64 goes west of the straight line. The other option is to get onto I-64 south of Louisville but that is longer in mileage because I-64 goes east before it goes south and it will therefore take longer to drive.
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