I watched the recording of that board meeting to see if they had any more details about the Lechmere Viaduct speed restriction. Nothing in the slides, but this is what Phil Eng said: "Back to the Lechmere Viaduct, that currently has 2 speed restrictions, one in each direction, 10 miles per hour. By doing that work concurrent with this work would enable us to lift those speed restrictions. The plan would be to do that at the same time, addressing those speed restrictions on the Lechmere Viaduct. That work entails replacing some shims that were made of a material, HDP, it's more of a poly blend material, replacing that with steel, and doing some alignment work to address those speed restrictions during the same period."
Overall, not much detail on the reason for the speed restrictions still being there unfortunately (bad "shims", and some needed alignment work?)