I went looking for ways to straighten out the NEC between New Haven and Rhode Island.
http://goo.gl/maps/xixdE
Won't work:
-- I-84 looks cool on a map, but it would require a tunnel boring machine through some of the hills in Tolland County and lots of superelevation in others. Especially that huge hill between Exit 68 and the Willington rest area...that's going to have to be a 1.5 mile tunnel because there's no way around it that doesn't hit equally steep rise. RR's can't exceed 1% recommended grade, 2% max. Price becomes a killer with I-84 well exceeding the maximum. And you would have trouble keeping equal bi-directional schedules because EB has to so constantly climb hills it would run slower than WB which is almost constantly downhill. I think this one has a lot of unsolvable engineering problems because 2D straight line ≠ 3D straight line.
Will work:
-- Definitely the NYNE out of Hartford is very fast and straight. All grade crossings except for the 3 tough ones on Tolland Turnpike can be eliminated easily. You just probably have to do some relocation around Tolland Tpke. to get rid of those. Not hard, though, because that vast wasteland of 84/291/384 interchanges leaves a large canvas for reworking. I bet you could come up with 10 viable ways to do that one...it's almost a non-issue.
-- I assume your Bolton-Willimantic routing is a variation of the rail-on-384-median two-fer. Note that the highway proposal with 1000 ft. greenway median that nearly got approved in 2004 before the Army Corps spiked it was the north-of-Hop River routing. The south-of-6 routing you're following here was the one that required too many property takings for the locals to support. So you'd need to flip-flop that line on the map to about the same spot on the north side of 6 and the river, then meet up with the old ROW at Pucker St. and follow it downtown to the pair of NECR junctions. Otherwise you've got exactly the right idea here.
-- Your northerly route Willimantic-Plainfield follows the would-be 384 ROW to 395 almost exactly. That'll definitely allow HSR speeds...no question.
Won't work:
-- The NYNE/Hop River routing does require you to use the old ROW between I-84 Exit 65 and the 384/44/6 interchange, so you can't straight-line it between Manchester Ctr. and Bolton. You'd slam headfirst into a rapid 600 ft. rise on the straightaway drawn on that map, which is no-go. The old hairpin through Bolton Notch State Park is necessary to thread between those grades, so there would always have to be a speed kink there if you're going to Providence via Willimantic. I don't think that's a problem, though, given how straight the NYNE is out of Hartford and how straight it could be made from Bolton to Willimantic if it followed 384. Figure you've got continuous 125 MPH on the west side of the hairpin, and continuous 125 with bona fide long stretches of 150 along the 384 median to the east of the hairpin...so one single 60 MPH restriction is a drop in the bucket. It's only when the ROW never stops twisting, like the Shoreline, where the speed penalties add up.
-- Very difficult and likely impossible to do the southerly route to 395 paralleling the active Willimantic Secondary. You slam into several 400 ft. rises, which won't work with RR grades and would force a curvier route than you've got on the map. The Willimantic Sec. hugs the river and twists like it does because that's the way to avoids the hills. So you'll never get something straight enough through that terrain to be speed-competitive with the 384 median. Axe this one and go with the very feasible northerly route.
-- No way to continue the 384-running past Plainfield to Providence. The hills in Foster and Scituate, RI are extremely steep...a series of 500 ft. and 600 ft. rises not unlike 84 in Tolland County. And there's no way to fit highway + rail along Scituate Reservoir. The Reservoir is what killed the highway alone in the 35 years they were trying and failing to build it.
Will work:
-- The NYNE routing east of Moosup to West Warwick is very straight. I'd absolutely stick to the old routing here. Have to deal with the S-curve along the river in Warwick and do a lot of grade crossing eliminations on the last 10 miles, but it junctions very cleanly with the NEC and you'd be able to speed into Providence station faster here than the NEC itself because the Shoreline's S-curve in Cranston is worse and a bigger traffic clog with slow speeds into the junction. To jump from 384 to Moosup you would have to install a wye onto the P&W main right where 384 would cross Route 32, head straight down about a mile, and either wye again at the old one-way P&W/NYNE junction or straight-cut around Moosup Pond (and the houses there) to meet up with the NYNE where it straightens out north of Route 14. I think straight-cutting works here if the NIMBY's don't kill it because downtown Moosup is a curve-a-thon and the old P&W/NYNE junction is on a very sharp angle. I don't think the speed restrictions of a P&W jog would be bad if you made the two wye curves wide enough to hit at 40-60 MPH. For Regionals you'd probably want to have a station around here anyway to serve transfer traffic on P&W and park-and-rides from the 395/384 interchange.
Whither Worcester?:
-- If you want a Worcester leg you've got two dilemmas: run all traffic through that Plainfield-via-384/P&W junction and do an L-shaped routing north, or reactivate the Air Line between Willimantic and Putnam and get a straighter shot and a shorter Putnam-Worcester P&W jog. P&W would absolutely support 125 MPH speeds most of the way because it's so very straight north of Plainfield, and avoids the hills that would tax the speeds on EB trains running on your I-84 routing.
-- The Air Line gets the straighter-line path out of Hartford/Willimantic, but would need a lot of curve straightening because it threads the needle around some mid-sized hills. Same 2D straight line ≠ 3D straight line problem, to lesser degree, as the 84 routing. The old Air Line wasn't exactly all it was cracked up to be as an old-timey higher speed bypass because of those Eastern CT hills. I think you could finesse it a bit, but it's never going to be so straight through Windham County that it can more than 90-100 MPH at most (with some 60 MPH restrictions).
-- So I think, even though the L-shape out of Plainfield looks much more indirect a map, it does take the crown as fastest Hartford-Worcester shot (by a hair) over any other route if P&W gets the right north-south upgrades. You can definitely do 125+ and 150 in good stretches the whole length from Hartford to Plainfield, and P&W is straight enough for 125 in most places. And would allow for maxing out the infrastructure here where a split in Willimantic would make the traffic a little too diffuse and too far below track capacity through Eastern CT.
So, to recap...most viable:
1) NYNE/Manchester Secondary Hartford-Bolton Notch on existing ROW, except for rework around 84/291/384 interchange to zap grade crossings. 125 MPH (ROW geometry would support 165 MPH segments, but figure dense commuter rail traffic/station spacing out to Vernon); 60-80 MPH through Bolton Notch (1 mi.).
2) 384 greenway median, Bolton-Willimantic. 125-165 MPH range.
3) Short stretch of NYNE + NECR ROW, downtown Willimantic (< 1 mi.). 40-60 MPH, within Willimantic station approach limits.
4) 384 greenway median, Willimantic-Plainfield. 125-165 MPH range.
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5a) SB wye from 384 onto P&W in Plainfield. 40-60 MPH, within Plainfield station approach limits.
6a) P&W for approx. 1 mi. 80 MPH.
7a) EB wye in Plainfield onto NYNE. 40-60 MPH.
8a) New alignment for 3/4 mile in Moosup to avoid curves (if it passes NIMBY + environmental muster). 90 MPH.
9a) NYNE/Washington Secondary existing ROW to NEC, with grade crossing eliminations. 125-150 MPH Eastern CT/Western RI, 80 MPH Warwick-Cranston around curves and dense commuter rail traffic.
10a) Existing NEC to Boston. 125-165 MPH.
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5b) NB wye from 384 onto P&W in Plainfield. 40-60 MPH, within Plainfield station approach limits.
6b) P&W active ROW to Worcester (maybe a couple short/< 1 mi. bypasses in downtown Webster and Auburn adjacent to 395 to zap some grade crossings). Some--but probably not 100%--other grade crossing eliminations. 110-125 MPH.
7b) Existing Worcester Line to Boston. 125 MPH, tri-tracked Worcester-128 and in Allston, grade separated Ashland/Framingham.
