STATE TRANSPORTATION OFFICIALS said on Monday they plan to install a prefabricated, temporary bridge to minimize traffic delays while the heavily used North Washington Street Bridge between Charlestown and Boston’s North End is being rebuilt.

Jonathan Gulliver, the state’s highway administrator, said the contractor overhauling the structurally deficient bridge came up with the idea as a way to shave about six months off of the five-year construction time. He said the temporary bridge will be located just to the west of the existing bridge and have the same capacity. He said the temporary bridge will not increase the cost of the project.

“This isn’t costing us anything,” Gulliver said, noting that the contractor, J.F. White, also plans to relocate a playground on the Charlestown side of the bridge to accommodate the new temporary bridge replacement. The base cost of the contract is $177 million, but with contingencies and other charges included the total cost is expected to top $200 million.

The temporary bridge will allow the contractor to do all the bridge work, including replacing the supporting piers, without trying to keep half of the span open while working on the other half.

The state had been forecasting moderate to significant delays while the bridge work was being done, particularly when it was cut down to just one lane going in both directions for a brief period next year. Jeffrey Gonneville, deputy general manager of the MBTA, said the replacement bridge will help avoid delays of as long as a half hour for the many buses that use the bridge.

The bridge announcement comes as state transportation officials are facing heavy pressure from Chelsea and other communities about lengthening commutes as repair work is done on a host of projects in the area, including the Tobin Bridge, the Alford Street Bridge, and the Chelsea viaduct, the elevated portion of Route 1 just north of the Tobin.

Chelsea officials, activists, and even one member of the T’s Fiscal and Management Control Board have complained about the transit agency’s lack of focus on the issue. The board member, Brian Lang, said he was concerned the T was ignoring concerns in Chelsea because most of the residents are working class immigrants. He focused most of his ire on the Route 111 bus, which carries roughly 12,000 passengers a day as it travels from Everett through Revere and Chelsea, over the Tobin Bridge, and into Boston via the North Washington Street Bridge.

The anger mobilized T officials. They say their research indicates 80 percent of the Route 111 bus riders transfer to the Green or Orange Lines at the route terminus at Haymarket. The T is offering Chelsea residents a heavily discounted fare to riders who take the commuter rail from Chelsea to North Station and then transfer there to the Green or Orange Lines.

MBTA General Manager Luis Ramirez announced on Monday that he is also launching a Chelsea regional transportation task force to jointly address issues that arise during the upcoming construction. Gonneville said the T has had some success in addressing problems recently, with the 111 bus running on-time 78 percent of the time. He said the 111 has been the second-highest-performing bus of the transit agency’s key bus routes.

Joseph Sullivan, a member of the Department of Transportation board and the mayor of Braintree, said he worried about all the work being done at the same time in such a small geographical area. He noted the Wynn Resorts casino in Everett is scheduled to open in mid-2019, which could add to congestion in the area.

Transportation Secretary Stephanie Pollack acknowledged a lot of repair work is being done at the same time, but she said the timing is being choreographed to minimize traffic disruptions. Gulliver said work on the Alford Street Bridge is scheduled to be completed by April 2019, several months before the casino opening.

Gulliver said the state is doing all the repair work because it is needed. “This is what catching up with your maintenance looks like,” he said.