BOSTON (SHNS) – MBTA officials announced late Thursday night they would immediately impose speed restrictions across all four subway lines following a Department of Public Utilities site visit, an unprecedented step that will cause immediate disruptions for riders.

“Tonight, the MBTA has announced speed restrictions between 10-25 miles per hour on the Red, Orange, Blue, and Green Lines effective immediately,” the T wrote in a press release published at 10:03 p.m. “The speed restrictions are the result of findings following a recent site visit of the Red Line between Ashmont and Savin Hill by the Department of Public Utilities.”

In a subsequent tweet, the T said the widespread slow zones will be imposed “out of an abundance of caution.”

“The MBTA remains committed to operating the transit system in the safest manner possible. Riders should plan for additional travel time while we work to address these findings,” the agency said. “We apologize for the inconvenience and will provide more information as it becomes available.”

An agency spokesperson declined to offer details about what the DPU found that prompted the immediate slowdowns. Officials scheduled a press conference for 10 a.m. Friday morning at the MBTA’s headquarters in Boston to discuss the developments.

“The Interim GM will provide more information tomorrow morning about these steps being taken out of an abundance of caution,” spokesperson Lisa Battiston said. “The MBTA wanted to provide this information tonight to allow customers to plan their morning commutes accordingly.”

The DPU serves as the designated state agency responsible for safety oversight of the T. When Federal Transit Administration investigators flagged widespread problems at the MBTA last year, they also criticized the DPU for falling short on its oversight responsibilities.

The late-night announcement follows months of intense scrutiny on the T’s safety failures fueled in part by the federal probe, which found staffing shortages, a deferred maintenance backlog and other issues.

MBTA officials late last month began publishing data on subway slow zones — where trains are limited to lower-than-typical speeds due to infrastructure defects — that have frustrated riders for months.

As of Jan. 31, 2023, a total of 8.7 miles of track across the MBTA’s Red, Blue, Orange and Green Lines, representing 6.5 percent of the system, had some kind of restriction in place limiting speeds to anywhere between 25 mph and 3 mph.