The Green Line’s D Branch trains will be replaced with shuttle buses starting Monday until Dec. 20 as part of the Massachusetts Bay Transportation Authority’s Track Improvement Program, agency officials announced.

The shuttle buses, free to the public and accessible for individuals with disabilities, will travel from Kenmore to Riverside stations all day from the start to the end of service over the 10 days, transit officials announced. The morning rush hour buses will run from Riverside to Woodland to Copley from 6-10 a.m. on weekdays while the evening rush hour ones will run from Copley to Woodland to Riverside from 3-7 p.m. during the week.

Express shuttles will depart from Riverside and Copley on the hour and half hour. The buses will stop at every D Branch station except for Beaconsfield, due to the narrow roads in the area. Officials encouraged those going to Beaconsfield to travel on the Green Line’s C Branch to Dean Road, roughly a four-minute walk to Beaconsfield.

Full schedules will soon be published on the MBTA’s website, according to officials.

Agency officials warned commuters to anticipate longer travel times with the shuttles due to the mixed traffic.

Meanwhile, work to re-gauge the rails on the Medford-Tufts branch of the Green Line extension will not be complete Monday, as originally scheduled.

Riders will be forced to forgo train service, and, instead, hop on shuttle buses each night at 8:45 for at least the next week, with the MBTA granting the contractor an additional seven nights to continue the work, General Manager Phillip Eng announced Friday.

“Repairing our infrastructure is essential to providing a safe and more reliable trip for our riders,” Eng said in a statement. “Equally important is rebuilding public trust in our ability to deliver for them.”

Eng said the agency’s goal is to eliminate all of the speed restrictions by the end of 2024. The initiative also includes a suspension of downtown Green Line service between North Station and Government Center through Dec. 22 as a result of the Government Center Garage demolition.

“Our team is deeply committed to seeing this through and we thank the public for their patience as we move the T forward,” Eng said. “We will have a robust open house schedule to ensure the public has an opportunity to ask questions and learn more about the various projects throughout the year.”