The ROW geometry is exactly the same as before. So it's just the cleanroomed state-of-repair. The corridor hasn't been substantially renovated since 1979 when the most recent signal system was installed and the Somerville Jct.-Lowell trackbed was undercut to swap the Plate F freight clearance route here (replacing the Fitchburg Line + Fitchburg Cutoff when the Cutoff was retired for the Red Line Extension). So the layout of control points was from a different era, and most else was in a state of in-situ maintenance stasis sans any upgrading. Up until the earliest pre-prep work for PTC the line annoyingly still retained an asynchronous south-of-Wilmington speed limit of 70 MPH one direction vs. 60 in the other. It's all evened up to standard-spec Class 4/79 MPH now (individual speed zones below the max will vary by geometry, but at least they're the same in either direction now).^ THere's all kinds of new crossovers, control points, & signals (including ones that have been obsoleted by PTC/Cab Signals), but I wonder how much they've actually been straightened? They've clearly benefitted from new & better drainage, new ties, and clean ballast (and way less scrub and trash trackside). (if we get too deep into CR, I'll move this to the "GLX impact on CR" thread that hasn't seen much action since the initial disruptions, Phase 1 bridge and trackside work, and the announcement of single-tracking and weekend bustitution)
Also the old unused rusting 3rd track scattered throughout the ROW is gone.
For historical purposes, that "third track" was called the Fourth Iron running from Mystic Jct to Somerville Jct (where the abandoned Freight Cutoff came in). After a 12/21/01 derailment of DOBO just
north of Walnut Street, Guilford never fixed it up and it went fallow from Walnut Street to Somerville Jct - never to be used again. This required all Guilford/Pan Am to use the handthrow crossover at
Walnut Street (which only connected the southbound or No.2 Track to the 4th Iron) all year in all kinds of weather instead of coming in and out on signals at Somerville Jct. And of course, this created
single track operations between Somerville Jct and Tower A for passenger trains when freights were active.
I'd guess it'll be topped by a fence whose purpose is to allow the two sides to be treated independently for worker-safety rules (CR won't have to slow if GL is being worked on and vice-versa). Ditto the CR not having to slow if people crossing the GL grades (on the GL side)What's the purpose of the low-rise concrete wall/curb between the commuter rail tracks and the Green Line?
The CR and GL have different requirements for horizontal and vertical curves, as well as clearance under bridges, etc. I'm sure they tried keeping the adjacent lines as close in elevation to each other as possible, but curb walls inevitably were required.. especially considering the need for flat egress/maintenance walkways outside of the clearance envelopes.. so ballast couldn't simply be sloped between CR and GL.What's the purpose of the low-rise concrete wall/curb between the commuter rail tracks and the Green Line?