Jeff Smith wrote:The interlocking at Shell was the same since the days of the NYNH&HRR until MNRR updated the operational alignments so that Shell was basically "halved" as far as I know; Noel can verify. And you don't need to update the alignment just because MNRR or SLE might run trains to Penn, although not in the convoluted way that you described. No one's going to build a flyover there; it was looked at and too expensive if even possible for the benefits gained. The current alignment works pretty well in my non-railroader opinion.
I have ridden through the area many times this summer. From my non-engineer perspective, the area east of Shell and west of New Rochelle station seems pretty constrained. A flyover starting west of New Rochelle station would need a stiff grade to rise high enough before reaching the I-95 overpass. Furthermore, any flyover in that area would involve replacement of the local road overpasses with much taller structures. These rebuilt road bridges likely wouldn't touch down where they presently do in order for their vertical profiles to stay within acceptable limits.
In contrast, the ROW east of the station seems much roomier. From my armchair, this invites an interesting possibility for a reconfigured Shell interlocking and New Rochelle station leading to a flyover in the area between today's New Rochelle and Larchmont stations. In this vision, the New Haven line would narrow to three tracks east of Pelham station. This would open up space for the Hell Gate line to remain at grade parallel with with the New Haven line tracks until New Rochelle station. At New Rochelle station, platforms and tracks would be arranged as follows from north to south:
Westbound side platform
Local track to GCT
Express track to/from GCT
Local track from GCT
Island platform
Hell Gate westward track
Hell Gate eastward track
Side platform
East of New Rochelle station, the Hell Gate tracks would fly over the eastward New Haven line mains then tie in to the New Haven line.
Granted, some ROW widening work in the station area is probably unavoidable no matter where the flyover goes. To that end, the road bridges around the area would have to be redone, and some retaining wall work would be needed around the station area. However, even if rebuilt to widen the rail ROW, the road bridges would probably be able to have not-so-dissimilar vertical profiles, which would save a lot of headache and cost. Obviously, the track curvature in the area would not be much improved. However, this plan would eliminate the crossing moves at the present at-grade junction. Since the diamonds would be eliminated, the New Haven line to/from GCT would now have 3 tracks good for 50 mph, as opposed to 2 today, and moves on the Hell Gate line tracks would be likely able to be sped up too.
I am under no pretense that any Shell flyover is going to happen before East Side Access wraps, but I do envision some sort of flyover in the area being called for by the 2020s or 30s. I am interested to know if something like what I laid out above has ever been studied.