The protected north-south bike lane has specialized traffic signals and turn lanes.
Reviews have been mixed: Cyclists are excited to have a designated path through the busy downtown area, but drivers are complaining about losing a lane of traffic.
"It's going to create additional traffic down here and already Chicago traffic is not good," said Tracy Patterson.
"Anytime you put something out there like this there's an adjustment period," said Chicago Department of Transportation's Gabe Klein. "Change is hard, even on a street like Dearborn with not enough cars and too much space."