Day 1 of Pikeocalypse wasn’t as bad as expected. What does today hold?

Jennifer Pline left her home in Wellesley two hours early on Monday, prepared for the worst. But her drive to her office in downtown Boston took only 50 minutes, about 15 minutes longer than usual, and afforded her a dramatic view of the giant steel beams being hoisted into place on the Commonwealth Avenue bridge.

“I was really expecting carmageddon, so I’m doing all right,” she said.

In fact, the Monday morning commute, the first major test of the Massachusetts Turnpike lane closures caused by the replacement of the Commonwealth Avenue bridge, went so well — with much shorter delays than expected — that officials are now worried about drivers returning to their old routines and flooding the highway on Tuesday.

At a press conference, Jonathan Gulliver, the state’s acting highway administrator, urged drivers not to let Monday’s commute fool them into thinking it will be smooth sailing for the rest of the week while lanes remain closed. Warning that delays of 90 minutes were still possible, he urged drivers to continue using public transit or alternate routes.

“Give yourself plenty of extra time,” Gulliver said. “Make sure you know well in advance what you could be up against.”

The region had been bracing for nightmarish gridlock as traffic was narrowed on the Pike to allow construction crews to replace the crumbling bridge, which was built in 1965 and spans the highway.

The Allston stretch of the Pike has been cut to two lanes in each direction until Aug. 7. During overnight hours, between 7 p.m. and 5 a.m., the highway will have one lane going east and two lanes going west. After Wednesday, the overnight configuration will shift to two lanes east, one lane west. The nearby BU Bridge is closed to non-emergency traffic until Aug. 14.

Construction on the eastbound side of the Comm. Ave. bridge and both directions of the MBTA Green Line B track is expected to last through Aug. 14. The MBTA is running shuttle buses between Babcock and Blandford streets during the construction. The westbound side of the bridge will be replaced in the summer of 2018.

Joe Pesaturo, an MBTA spokesperson, said Monday’s commute on the Green Line “went well.”

“The bus shuttles ran smoothly and all Green Line passengers were accommodated,’’ Pesaturo said.

Inbound traffic was heavy Monday morning on the Massachusetts Turnpike.Pat Greenhouse/Globe Staff

While inbound traffic was slow Monday morning and backed up for several miles, the commute was actually “a little bit better” than expected, Gulliver said.

“That means, I think, a lot of people have taken our advice and have either shifted their travel times or taken a different mode of transportation altogether,” Gulliver said. “But regardless, there is congestion.”

Mondays in the summer are often light travel days, which may have also eased commuter delays.

Joshua Ledwell, a software designer, said the drive from his home in Maynard to his office in South Boston took him 85 minutes on Monday, rather than the usual 60 minutes. The Waze app, he said, directed him to avoid the Pike and take Route 2 and Storrow Drive.

“It was pretty bad,” he said, but “not quite apocalyptic.”

Still, the project has been disruptive, said Marc Berkowitz, owner of Sunset Grill & Tap on Commonwealth Avenue.

Business at the Mexican restaurant has dropped between 20 and 30 percent since last week when the construction started, Berkowitz said. He gave employees the option to take extra vacation time, he said, and about a third of his staff took the offer.

“Everyone’s trying to do the best we can,” said Berkowitz.

Berkowitz commended state transportation officials for the speed of the project and for meeting with business owners in advance of the construction.

“You know it doesn’t give us back the business, but at least they’re organized,” he said.

Sunset sits on the corner of St. Paul Street, which is still open to pedestrians and vehicles, Berkowitz said. But the confusing construction and closures have kept people away. “So far it’s easy enough walking, but people are just being told ‘Stay away,’ ” he said. “Our hope is that people will figure it out.”

Traffic was reduced to two lanes each way on the Pike Monday as construction continued on the Commonwealth Avenue bridge.Keith Bedford/Globe Staff

With construction cranes as a backdrop, a group took part in a circuit training session on the closed Boston University Bridge.Pat Greenhouse/Globe Staff/Globe Staff