The train was crossing over a switch point when part of the train followed the correct track and another part of the train followed the wrong track, a CTA spokeswoman said.
No injures were reported and CTA power is back on after a Brown Line train "split the tracks" Tuesday morning about a half block north of the Belmont station.
Officials say seven passengers were reportedly on the northbound train, and three EMS crews were on the scene to help walk them off the tracks back to the Belmont station. Everyone was safely evacuated.
A CTA spokeswoman said the train was crossing over a switch point around 8:45 a.m. when part of the train followed the correct track and another part of the train followed the wrong track. Three cars made the turn, but the fourth car kept going straight.
The fourth car has since been moved to the correct track. The Red Line northbound track was checked for any damage.
Passengers also were stuck on trains between Wellington and Belmont as a result of the derailment. Red, Brown and Purple lines were stalled.
The CTA provided shuttle service until 11:45 a.m. in the Belmont area while crews investigated.