At least when the major SGR projects are complete you are left with a higher-capacity RR than it has ever been at any time since the atrophy-years NYNH&H in the mid-1960's. It can't be overstated what >50 years of tying one hand behind back on deferred maint has done. The gains are indeed significant from the cruft rollback. The cat replacement project is particularly underrated for service reliability, as summer "wire sag" season used to be torture for all the heat-related speed restrictions that would get slapped all up and down the line. When wire contact reliability faded, it was the multi-pantograph EMU sets that took it on the chin which completely effed up the single-fire express lane for Amtrak. 3+ months of the year you couldn't maintain service reliability commensurate with the other 9 months of the year. That madness is gone now. The segue straight into WALK Bridge replacement off the final completion of the constant-tension cat megaproject puts a few more years of construction staging between having that newly gained full-service capacity, but it's a worthwhile wait because that bridge will likewise be a thinner/sturdier deck with higher clearance, with variable-height raisings that will extremely-rarely need to go to full height (since squat barge traffic is the bulk of Norwalk River's maritime use), and faster-overall raisings with far less glitchy resets. Stamford-Norwalk is the second-busiest segment to New Rochelle-Stamford...so proportionately that bridge is biggest single capacity improvement on Segment #2. Just as SHELL separation + Cos Cob replacement are the biggest on busiest Segment #1.Full disclosure. I worked the Corridor for 42 years. One of the constraints on MNRR is that it has not been at 4 track capacity for just about all of my years working it. There was a time when MNRR contemplated going to three tracks east of Stamford and downgraded the speeds on track 4 because they stopped maintaining it. After some improvements financed by Amtrak, the tracks were upgraded , just in time for a massive catenary project, which has further restricted capacity. All of this work was occurring while the Acela was introduced, and Metro North growth was exploding; all good things. I know for a fact that transit times can be reduced ( with an experienced engineer who knows where to cheat) but speed observance is now much more strict ( as it should be). As the catenary project finally comes to completion, we will have further track restrictions to re-build South Norwalk movable bridge. There was a time when MNRR dispatchers were not kind to Amtrak,especially the Acela. I think we were looked upon as an added burden. One Rail Traffic controller used to routinely chime " ties go to he home team", when we were made to wait for MNRR moves. Also, I do believe Amtrak is better treated on MNRR after the RTC's got to know the Amtrak crews they knew who could make a run and not ball up the works. Further cooperation is sure to increase if and when MNRR runs to Penn Station on the Hellgate Line. Speeds CAN be increased on MNRR,but the tracks will have to be maintained to higher standards than currently employed by MNRR, and civil track restrictions CANNOT be protected with the cab signal system. It treats a 45 MPH curve like a train and unnecessarily slows down traffic for much longer distances than with the PTC system Amtrak uses on tracks it owns.
It's all downhill and wind-at-backs from there. Norwalk-Bridgeport is comparably a much more manageable segment because all the max-density Stamford locals have long since dropped off, the Danbury trains have dropped off, and you haven't yet picked up any Shore Line East, Waterbury, or (future) Hartford Line slots until Bridgeport. Bridgeport-New Haven is the easiest because wetlands and a *little* relaxing of the megalopolis density give it comparatively much lower station density and not quite as much signal-block density, so the moderate service uptick and increased presence of diesel locals does no harm because passing opportunities are comparably much more relaxed. The biggest needs here are mainly extending all platforms to 10 cars commensurate with Stamford-west to minimize dwells through 30 more years of projected growth. The handful of remaining 4-6 car stubby platforms extract their own inefficiencies on EMU sets that routinely run longer than that. The bridge replacements east of Norwalk could even be done as fixed spans if the feds were willing to pump extra into Devon and Sagatuck fixed replacements for changing the approach grades and rebuilding Westport Station on a higher elevation (so far in all plans they've been anti-help and are sacking ConnDOT with majority share, so hope is not as of yet a good thing). If that's done 2 more bona fide speed restrictions (if not exactly consequential number of openings) get zeroed out, and New Haven-Norwalk dispatching more or less zeroes out any bridge opening potential in the schedule since 1998-construction PECK Bridge in Bridgeport is a far-and-away least concern that only opens 2-4 times per month (if that).
The signaling density constraint is real. There is very good reason why this is the last NEC segment of all to have PTC go live; keeping the interplay with the cab signals at "do no harm" baseline took years of additional design work because traffic density was already sitting at technological limits. Survey the world and you won't find a comparable analogue for how tight the packing is on the express tracks of a 4-track RR. In any other application the service pie has a lower proportion of commuter expresses and higher proportion of intercity/HSR than here...and so the terms of the signal layout start with looser blocks that can differentiate a much higher overall express-track speed vs. the local tracks, all else being equal. This is not one of those cases where bureaucratic competency or Jetsons Shit signaling is going to open up a new speed tier that doesn't already exist. Nobody else is forced to 'run against the taillights' on margins this tight, and traffic modelers with world experience will be quick to point out that the New Haven Line is a legit world's-trickiest in service layering that will behave much the same even in perfect laboratory conditions. The delicate balancing act is predicated on well-behaved single-file of all Amtrak and all NHV expresses on those extremely crowded west-of-Stamford center tracks where every train is making no more than one intermediate stop. "Do no harm" was the best you could hope for with PTC interoperability, and now that we more or less have that with the finished PTC install it's now it's up to cueing up changes like SHELL interlocking separation and Cos Cob replacement to carve out any more headroom for 'running up against the taillights' at tightest laboratory margin.
That does model out as for-real good enough for the NEC FUTURE service layer cake, and then with the Stamford-Norwalk, Norwalk-Bridgeport, and Bridgeport-New Haven segments being of comparatively lower-difficulty dispatching makes the backfill work across the rest of the corridor more or less academic. Nothing unique those segments will throw Amtrak's way will ever match the difficulty of maintaining max-tight margins to Stamford. But it was a long time coming to see as much light at the end of the tunnel as we even have now with the new catenary, WALK replacement, and SHELL + Cos Cob graduating to the realm of real nuts-and-bolts funding arguments rather than fantasy/conceptual argument. The solves for readying the New Haven Line for NEC FUTURE are much more concrete and actionable than pretty much everywhere else...including Gateway NYC which the Heritage Foundation zombies populating USDOT leadership are now trying to vainly kill yet again. Stay on-focus and we can settle up the CT megalopolis bucket list in realistic due time.