Workers have been on site around the clock for over a week trying to finish the job on time. The work was nearly complete Sunday night and the track was ready to get back open for business.
At 4 a.m. Brown and Purple Line trains once again crossed the Wells Street Bridge into and out of the Loop.
"Definitely relieved. It made late to work like six times," said Dillon Perry.
The reopening marks the end of nine days of work to replace the bridge's 500,000 pound southern half, as well as the tracks just south of the bridge.
"I'm a patient guy. I'm like, whatever needs to be done," said Jeff Brown.
Not everyone is so tolerant though. For a week and a half, CTA Brown Line users have had to take shuttle buses to get in and out of the loop, as trains have only gone as far as the Merchandise Mart, Chicago Avenue on the weekends.
The Purple Line express has not run at all during that time.
"Not too bad. I don't work in the Loop but I have appointments downtown. It was slow last week," said Robert Meyers.
The work is not done yet. The bridge will close again to Brown and Purple Line trains when the northern half of the bridge is replaced. That work will start on April 26.