19th-century pieces of wood are forcing a ‘huge’ train shutdown in Boston. MBTA officials explain why

MBTA officials shared more details Thursday on why they are shutting down an extensive section of the Green Line through the heart of Downtown Boston for half of December.

The T needs to replace a 130-year-old piece of the Green Line tunnels that houses the trains’ overhead wires. Described as a wooden “trough,” it has been there since the line was first constructed in the late 1890s.

To complete the work, the agency plans to close the central core of the Green Line from Dec. 8 through Dec. 22.

Completing the work is “vital,” Massachusetts Transportation Secretary and MBTA General Manager Phillip Eng said in an interview Thursday afternoon. The two-week closure, he said, was the most minimally disruptive way to schedule the project.

The trough — installed 20 years before President Jo