ALSTEAD — Work is underway on a many-month, $1.1 million project to replace the Route 123A bridge over Warren Brook in town, the N.H. Department of Transportation announced Friday.

Single-lane, alternating traffic will continue as the bridge is removed and replaced one half at a time, according to a news release from the state agency, which says temporary traffic signals will be used. The bridge is near the intersection of Routes 123 and 123A.

The project is expected to finish in October 2019. The work began this week, according to N.H. Department of Transportation spokesman William H. “Bill” Boynton.

Cold River Bridges LLC of Walpole is the project’s contractor.