The State Department of Transportation intends to start replacement of the Bloomfield Avenue overpass, which spans the NJ Transit tracks near the Bay Street train station, on Oct. 3.

Drivers and mass transit users in the Montclair area can expect some service cancellations and detours.

Single-lane closures on the bridge will happen at night for the duration of the work.

The repair work will result in train service between the Bay Street station and all points east being canceled for safety reasons on 12 weekends. Township communications director Katya Wowk said the weekends may not necessarily be consecutive ones. NJ Transit will provide a shuttle bus service provided between stations to bypass the work zone, she said.

Later in the spring, the sidewalks on the overpass will be closed off. A shuttle service will be provided for pedestrians, including Glenfield Middle School students, needing to cross the bridge from one side to the other.

The overpass was originally built in 1911 and sees on average 23,370 vehicles a day, according to a 2015 report from the nonprofit group Transportation for America. The report gave the bridge a rating of “structurally deficient,” with each of the bridge’s three sections  - deck, superstructure and infrastructure - receiving a rating of four out of 10.