North Springs is the furthest you can travel north on MARTA rail. The station is outside the perimeter (I-285) and next to Georgia 400. At the North Springs Station you can transfer to buses that will take you further north to Roswell and Alpharetta. Or use Uber, Lyft, Zipcar or taxi to reach Roswell, Alpharetta and East Cobb within 15 minutes.
To see all your commute options, use Google Maps.