One of the most popular bus routes in the region is about to change.

The Coastal Link route, which provides service from Milford to Norwalk, will be running every 30 minutes instead of every 20 minutes on weekdays, Greater Bridgeport Transit officials say. The change will take effect on Sunday, Jan. 28.

GBT CEO Doug Holcomb said Wednesday the change was necessitated by increasing congestion along the route, combined with an effort to make the service more reliable. There is no change to the route itself.

“We were having a hard time providing reliable service at a 20-minute frequency,” Holcomb said.

“So we talked to the public and we asked them if we could give it a try — providing a less frequent but more reliable service.”

The Coastal Link route employs buses from three different transit districts — GBT, the Norwalk Transit District (Norwalk Wheels) and the Milford Transit District.

About half of the buses that service the route are from GBT, with MTD and NTD splitting the remaining 50 percent.

Most of the route sits along Route 1.

The Coastal Link was known as Route 2 before 1998.

The portion of it that runs through Stratford, Bridgeport and Fairfield was operated by the former Bridgeport Transit Co. many years ago.

“The original Coastal Link schedule was developed in the late 1990s and much has changed since then,” Holcomb said.

Also, after the change, all of the buses will travel the full length of the route; with the current schedule, a few of the Coastal Link buses didn’t travel the full 18 miles.

There will be no “short turns” at the Dock Shopping Center and at Bulkley Avenue in Westport.

There will be more than 30 departures daily from the Water Street Station in Bridgeport to the Norwalk Wheels Hub and to the Connecticut Post Mall in Milford.

At any given time, seven buses travel the route.

Holcomb said the Coastal Link carries more than 100,000 riders a month. The only route with more riders — Route 8, which runs up and down Main Street between downtown Bridgeport and the Trumbull Mall — has more. In Norwalk, riders can make connections to Stamford bus service and in Milford, riders can make connections to New Haven.