A commuter rail line recently opened between Hartford and Springfield MA.
Some information here:
https://en.wikipedia.org/wiki/Hartford_Line
I thought it was kind of interesting. There are some similarities to a possible Halifax line and some differences.
This project involves restoring two-way track along a route that was previously reduced to one track, so similar to the line through the rail cut. It is quite a bit longer at 100 km and it will run at speeds of up to 180 km/h, which is interesting. High-speed rail gets a lot of attention but it's good to remember that "medium speed" rail is possible too (in comparison to the ultra-slow rail we currently have) and it is much cheaper.