SAN DIEGO — As a 57-hour-long closure of southbound lanes at the San Ysidro border crossing got underway Saturday, officials said it seemed to be running smoothly and asked the public to continue to avoid the area.

From 3 a.m. Saturday morning to noon Monday, all southbound traffic on the two parallel interstates are being rerouted onto SR-905 as part of a modernization and expansion project at San Ysidro Port of Entry, according to the U.S. General Services Administration.

Drivers traveling to Mexico through San Diego over the period are advised to use Otay Mesa Port of Entry, about nine miles east of San Ysidro on Via de la Amistad.

Many anticipated longer than normal wait times at the Otay Mesa crossing, but as of Saturday night, detoured traffic was running smoothly, with no major backups.

“It’s going smooth and we really appreciate that the public really got the message and it seems that the traffic demand for the system is lower than usual,” Mario Orso of Caltrans said.

“It’s a pleasant surprise. I think the public has really heeded the warning and they’re not crossing,” Anthony Kleppe of the U.S. General Services Administration said.

Even northbound traffic from Mexico into the U.S. at the San Ysidro crossing was lighter than usual.

“We can see from here the end of the line of vehicles queuing for northbound entry,” Kleppe said. “Generally, that line is far greater. Generally, at this time of day, we would expect to see 45-minute to hour waits to cross the border. Now we see five or six cars in line so it’s a lot shorter. People are staying away.”

The closures will allow construction crews to disassemble a southbound vehicle-inspection canopy over I-5 at the San Ysidro port, considered the busiest border crossing in the world. Additional road work and installation of underground utilities also will take place as part of around-the-clock operations during the closure.

“At this point, really everything is going according to plan,” Kleppe said. “In the background, you can see that we’ve been able to pull a lot of the infrastructure that was in the roadway out…lane separation, crash barriers, the big 6,000-square-foot steel and canvas canopy are all gone now. Now we’re doing some saw-cutting in the roadway for utility installation and working to get the roadway ready for Monday at noon.”

At the San Ysidro pedestrian border crossing, lines were also shorter than expected.

“I thought it would be like an hour, maybe even like a three- or five-hour pedestrian line, but it was fast,” Norbert Garces said. “It only took me like 30 minutes I think.”

Crews are ahead of schedule, and to ensure everything continues to run smoothly, officials say they need the public’s continued support.

“They’re staying off the road and that’s really critical as we go through today and tomorrow,” Kleppe said. “I think a lot of people are thinking, well gosh, it’s not looking that bad today, maybe I’ll travel tomorrow — we’re really asking people to continue to stay off the roads, keep the area clear.”