The T today finally released a list of all slow zones in the system and it is not pretty.
www.nbcboston.com
MBTA SLOW ZONES REPORT FOR JANUARY 2023 (PDF)

MAPS: Here's Where the T Has to Slow Down, in 1st Look by MBTA
The MBTA has released its list of slow zones on the T, revealing for the first time exactly where its trains have to slow down and by how much. The Orange Line has the highest percentage of track with speed restrictions — there are slow zones on 2.9 miles of its run from Forest Hills in Boston...

MBTA SLOW ZONES REPORT FOR JANUARY 2023 (PDF)