Crews completed bridge work on the busy 405 freeway nearly a full day ahead of schedule Sunday, allowing officials to reopen all lines along the 10-mile stretch of the Los Angeles roadway.
Traffic started moving just after noon, for the first time since being shut down at midnight Friday.
There were no major problems since the freeway was closed, despite warnings of a "Carmageddon" of traffic jams.
Mayor Antonio Villaraigosa thanked residents for heeding calls to stay away during the closure.
"I'm proud of this effort, I'm proud of what the people have been able to do, because without them and without their cooperation I would not be able to make this announcement today, and that is mission accomplished," said Villaraigosa.
The Metropolitan Transportation Authority says project contractor Kiewit Infrastructure West could have been fined a $72,000 an hour for delay in getting the freeway reopened. Instead Kiewit will receive an extra $300,000 for finishing early. The project will save $400,000, even with the Kiewit bonus, since paying workers for an additional 12 hour shift would have cost $700,000.