THE MBTA announced late Thursday night that it was immediately imposing speed restrictions on all of its subway lines following a recent state safety inspection of the Red Line between Ashmont and Savin Hill.

In a press release issued at 10 p.m., the T said all trains on the Red, Orange, Blue, and Green Lines would be required to travel between 10 and 25 miles per hour.

The T promised more information on Friday.

The system-wide slowdown is another major setback for a transit system struggling to address a slew of safety issues and deal with aging infrastructure.

At virtual subcommittee meetings of the MBTA board on Thursday, there were references to a Department of Public Utilities inspection on the Red Line that uncovered problems and resulted in an employee being disciplined for not wearing a hard hat. But there was no indication that the problems extended across the entire subway system.

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...