Good news for those girding themselves for another summer-long shutdown of the Sumner Tunnel: It will still be closed, but for just one month instead of the two months originally planned.

Highway Administrator Jonathan Gulliver made the unexpected announcement Tuesday.

“We are absolutely thrilled to announce that we are cutting that time in half and we will now be performing our work during a full closure between July 5 and Aug. 5,” he said.

The work during phase one last summer involved replacing the ceiling and support arches in the tunnel. Phase two this summer involves replacing the road surface inside the tunnel.

Gulliver said data collected this spring during weekend tunnel closures enabled engineers to refine the areas where full road replacement is needed, and they were able to compress the work into four weeks. He says the remaining work will be done during weekend closures later this summer and fall.

The mile-long Sumner Tunnel is a vital link in Boston’s highway network. Built 100 years ago, around 39,000 people use the Sumner Tunnel every day, traveling from Logan Airport and East Boston to the North End and downtown Boston.

The tunnel is in the middle of a two-year, $165 million reconstruction that Gulliver says will ensure its viability for another 50 years. Gulliver called the Sumner Tunnel rebuild the most “impactful” project MassDOT is undertaking this year.

As they did last summer, officials are urging people to find alternate routes or take public transit. MBTA General Manager Phil Eng said there are incentives — including discounted and free MBTA services — that will be provided during the full closure. For example, Eng said the entire Blue Line in both directions will be free to riders.

“The Blue Line is completely restriction-free now and operating at full line speed,” Eng said, noting the track work done last month. “So, sit back, relax and leave the driving to us.”

There will also be reduced fare or free ferry service from East Boston, Lynn, Winthrop and Hingham/Hull along with reduced commuter rail fares for riders on the Newburyport/Rockport Commuter Line.

Gulliver was asked why this year four overheight trucks became stuck in the tunnel, which is an unusual occurrence in the Sumner. Gulliver said they've noticed “a definite uptick in the number of trucks” going through the tunnel in recent months. In response, MassDOT is installing warning signs like those on Storrow Drive, as well as making sure the tunnel closure information is on all truck driver apps and contacting trucking associations to spread the word.

“We’re really trying to increase awareness, really trying to get them to avoid the area before they even get there and have to turn around,” he said.

If all goes according to plan, there will be the one month full closure in July and weekend closures excluding holiday weekends through the fall up to Thanksgiving, if needed, to get the work done.