Updated

The busiest border crossing in the United States reopened ahead of schedule Monday after a weekend shutdown for work on a $741 million expansion project.

Traffic began flowing again just after midnight on southbound Interstate 5 and connecting freeways at the San Ysidro Port of Entry connecting San Diego to Tijuana, said California Department of Transportation spokeswoman Caridad Sanchez.

The crossing shut down at 3 a.m. Saturday and the closure had been scheduled to last until noon on Monday.

The expansion was believed to be the largest renovation of a crossing along the nearly 2,000-mile (3,200-kilometer) U.S.-Mexico border. It has been in the works for years to ease congestion and boost cross-border commerce.

There were no significant delays during the closure of all Mexico-bound car traffic at the San Ysidro border crossing, where about 50,000 cars and 20,000 pedestrians go back and forth on weekdays.

Motorists were directed east to the much-smaller Otay Mesa crossing.

U.S. officials repeatedly warned travelers to avoid driving to Tijuana from San Diego during the shutdown.