Officials are still bracing for the worst of the Sumner Tunnel closure traffic, Gov. Maura Healey and transportation officials said, even as backlogs continue to build up.

“I think this whole week will be a test as we move into tomorrow and Wednesday and Thursday,” Healey said at a press conference at the Sumner Tunnel Command Center. “And all we can promise is that we’re going to continue to monitor the situation here. The command center is staffed. Crews are out there. They’re ready to turn on a dime in terms of adjusting diversions and the like.”

The two-month, full-time Sumner Tunnel closure began last Wednesday, but officials said previously diversion routes and public transportation would really begin to feel the impact as holiday-travelers return this week.

With an estimated 39,000 daily Sumner Tunnel drivers diverted, the full brunt of the closure reportedly may mean multi-mile backlogs along alternate routes.

The governor and others urged commuters again to “ditch the drive” whenever possible for the next two months. During the shutdown, officials have instituted free or reduced prices for the Blue Line, ferries, Commuter Rail, Silver Line and several buses in the area to encourage drivers to utilize public transport.

Healey said everything so far is going “according to expectations.” Highway Administrator Jonathan Gulliver noted Sunday that crews successfully completed the first phase of construction on time, and they anticipate finishing by the planned Aug. 31 reopening date.

In the Command Center, workers from MassDOT, emergency services and others monitored traffic conditions and made real time adjustments.

Gulliver noted Monday that traffic along major routes leading into city from the north was heavier than normal and peaked that morning around 6:30 a.m.

MBTA General Manager Phillip Eng said the Blue Line has had “light to moderate” ridership so far, and the trains had reportedly been running smoothly Monday morning.

Healey called the project a “huge undertaking” but said the nearly 100-year-old tunnel has “long been in need of restoration.”

“We appreciate the public’s patience with this,” Healey said. “We know this never comes at a good time.”

More information on the tunnel shutdown and diversions is available on Mass.gov/sumner-tunnel, and real time traffic information is available on the Mass 511 site and app.