The street portion of the bridge reopened shortly after 6 a.m.
Chicago Mayor Rahm Emanuel held a news conference Thursday to announce the end of the one-year project.
"It's a fitting testament, literally, almost about 100 years ago to finally rebuild the bridge to serve another century of Chicagoans commuting to and from work," said Chicago Mayor Rahm Emanuel.
Both the northern and the southern elevated train portions of the bridge were already replaced.
Construction workers and engineers removed the big orange barrels and were able to appreciate their finished product. During the process, the respected the architecture and history of the old bridge.
"I'm really honored to be a part of this project in the Loop of Chicago. It's going to be a great thing 30 years from now to bring my family kids down here and say I participated in this great project," engineer Michal Williams said.
Bike messenger Lionel Floyd was the first person to cross the bridge since November 5, 2012.
"It's a nice ride, smooth, nice concrete," Floyd said. "Everybody will be excited that the bridge is open today."
Moments after, the cars started coming - like the bridge had never been closed. Drivers and pedestrians are saying goodbye to delays.
"Does it affect you? It will cut 10 to 15 minutes off my commute," said Lisa Metzler, driver. "Makes it a lot easier to get to work," said pedestrian Pete Levine. "They made it look nice. Lots of lights fancy iron stuff. Nice to have it open."
CTA passengers have been able to ride trains back and forth over the bridge for several months.
It was a massive project. The Chicago Dept. of Transportation and the mayor both say it was done on time and on budget, costing $50 million. Giant pieces of the bridge were snapped in two like Lego pieces.
The old bridge was 92 years old. The new structure is now operational and freshly painted.