State officials on Monday approved a $205 million project to replace the century-old North Washington Street Bridge, launching a grueling five-year period of lane closures and construction that will ultimately install a new bridge between Charlestown and the North End.
Work to replace the rusty truss bridge will begin this fall and stretch until August 2023. The existing bridge, which costs more than $1 million a year in maintenance, is considered “structurally deficient,” meaning it’s close to the end of its life though not yet unsafe.
The new Charles River crossing is expected to feature improved infrastructure for pedestrians and bicyclists and two vehicle lanes in each direction, as well as one inbound lane exclusively for buses headed downtown from the north.
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Its skeleton-like design is meant to complement the nearby Zakim Memorial Bridge, which carries Interstate 93 over the Charles.
But getting to the new span’s opening day will be a hassle for the estimated 44,000 drivers who currently cross the bridge each day.
The bridge will be replaced in parts, with traffic shifting as the western and then eastern portions are dismantled.
During most of the project, two lanes will be open toward downtown Boston, with one lane outbound to Charlestown — though during certain periods only one lane will be open each way.
The project adds to a glut of traffic disruptions already scheduled for Charlestown in the coming years, including lane closures on a stretch of the Tobin Bridge starting next month and lasting on and off until 2020.
Meanwhile, the 2019 opening of the Wynn Resorts casino in Everett is expected to add traffic to an already congested Sullivan Square.
The bridge replacement also comes with a hefty price tag. The board of the Massachusetts Department of Transportation on Monday approved a base contract for J.F. White Contracting of $177 million — the low bid even though it was more than 9 percent higher than the state’s estimate.
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Police details, engineering, and a 10 percent contingency for cost overruns could increase the price to $205 million.
“We clearly estimated low on this one,” Transportation Secretary Stephanie Pollack said.
The City of Boston is slated to pay at least $14.9 million for the project, with the remainder coming from a mix of federal and state funds.
The city may pay an additional $7.2 million as an incentive if J.F. White can complete most of the work six months early. The contractor — also behind the long-overdue rebuilding of the Longfellow Bridge between Boston and Cambridge — will face fines of $40,000 a day if the project runs late.
Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter @adamtvaccaro.