BRIDGEWATER — The southern portion of Route 133, which 3,000 cars traverse daily, will close for construction for four and a half months in March.

Near the the Housatonic River, 5,200 feet of pavement will close to traffic March 13, and two detours are planned so drivers can get into town. One has drivers taking back roads. The other has people driving around the town entirely.

The project calls for more than 3,000 feet of road, near the town boat launch, to be moved and realigned for safety reasons, according to a Department of Transportation press release. The DOT will also build a 750-foot long retaining wall on the west side of the road.

One detour option, for passenger cars only, will push traffic on back roads west of 133. The official detour will have trucks and “hopefully most vehicles” drive around Bridgewater — taking Route 202 until it hits New Milford and intersects with Route 67 northwest of town, said First Selectman Curtis Read.

Town officials and the DOT are working together to make the concrete retaining wall aesthetically pleasing, Read said. Town officials will pick what color to paint the wall in coming weeks.

For the local detour route, along Northrup Street, the town will drop the speed limit by 10 miles an hour (from 35 to 25), install several speed bumps, and step up traffic enforcement, Read said.

Some residents have expressed concern about an uptick in traffic along Northrup and nearby roads, and Read is urging drivers to use the “official bypass” through New Milford instead of the back road route.

Once the route is fully re-opened, area drivers will cross bridge, connecting Brookfield to Bridgewater, and drive Route 133 unencumbered by construction — until Spring 2019.

Then, the state is scheduled to rehabilitate the 851-foot bridge, built in 1955. In 2015, the state found the bridge was structurally deficient and functionally obsolete. Rehabilitation will cost $7.1 million.

Read has said the bridge work won’t be as disruptive as the road project. Several repairs to the deck, joints and parapet along with drainage improvements and a fresh coat of paint will be complete by Spring 2020.

“We’ll have a spanking-new entranceway to Bridgewater by 2020,” Read has said.; 203-731-3411; @bglytton