That is a ludicrous route for high speed rail.

I don't really know this area. Say you wanted to build an entirely new and mostly straight Stamford - Waterbury - Hartford - Providence alignment. Some of that would need to be in tunnel. But how much of that could you do on the surface without needing to demolish too many houses?

That map is at least a little bit aspirational: it shows the Northeast Corridor extending north of Boston's South Station to North Station via "Central Station". While I would love it if we built https://en.wikipedia.org/wiki/North%E2%80%93South_Rail_Link it does not currently exist.

The main impression it gave me (be sure to toggle to the satellite view - then you can also verify the existence of tracks) is how tricky it would be to build a reasonably straight railroad there while also connecting the population centers.

The route that the existing track takes is insanely suboptimal and seems so hard to fix considering the existing urban sprawl in the relevant areas.

It makes most sense to me for rails to be built in the interstate medians. You see this in Chicago, and could be done elsewhere relatively easily as its already government owned land. As a bonus, car commuters could see how much faster HSR might be than their normal commute.

Interstate highways are designed for a speed limit of <100MPH and have the curves to show for it.

High speed rail goes well beyond that speed and needs much larger curves, at which point you're deviating enough from main roads you may as well just take a different path entirely.

Your not wrong, but not really right either. Interstate highways do allow tighter curves and do have them. However most of the interstate is straight or a gentle curve. Thus you can limit your land takings to near the curves and then rejoin the interstate. There is a good chance that the highway department will be interested in your new right of way to make the curve better too - a lot of interstates have curves that are too tight for highway use without slowing down. Many of the tight curves are also near places where you would want to slow down for a station anyway.

The above isn't a perfect answer to all situations, but it helps a lot.

Maybe in very flat areas where the interstate was preceded by nothing, but curves to avoid things in urban areas or for geographical reasons are more common. And HSR curves are gigantic; the Chinese build their HSR lines with curve radii of 4km. Texas uses a maximum of 1.4km curve radii and they have some of the fastest Interstates around.

The rail solution to that would probably be a tunnel. A tunnel is a cheaper affair with just two tracks than if it has to be wide enough for two tracks and six to eight highway lanes.

Urban areas are just a small minority of where the tracks need to go, as such if the train goes half the speed in the urban area we are still okay on overall trip time. In fact I suspect (read I don't know because it hasn't really been tried) that HSR should probably do a bunch of stops in the urban areas anyway so it won't get up to speed.

When I say "urban area" I mean the continuous built up urban area into the suburbs. American sprawl means that metropolitan areas are much further spread out than their European or Asian counterparts, to the point where most of Boston-Washington is sprawl and very little of it is farmlands.

In any case when you start building HSR it becomes progressively harder to eke out savings and the highest come from urban area speedups. Going from 50 to 100MPH cuts a lot more time than going from 150MPH to 200MPH. And the former simply doesn't work in the median of a highway.

The interstate highway along that stretch (I-15) does not seem to have enough space in the middle for that, unfortunately.

How are you ever going to achieve high speed if you are stopping every 10 miles for another station? There appears to be 8 stations in Baltimore alone.

There are four tracks - that enables the combination of a slow local stop-at-every-station service along with a fast feeder service.

But then the bizarre/historic track geometry ruins the fast service...

So the fast service shouldn't use that alignment. There must already be population centers that are skipped by the fast service - its tracks don't have to go through there either.

Today the fast services follow the same alignment.

Rerouting so far has been a headache; in New Haven-Boston where the tracks are so curvy new tracks have to be built, the FRA proposed going through entirely different population centers (the geography of the existing coast line is very challenging). This has resulted in an interesting fight where people want the train in their town, but also do not want the impact of newly constructed tracks through their town.

This map shows all the local stops for each city's commuter rail system. Intercity trains skip over many of these. The Acela leaves Boston, stops a the Route 128 suburban ring station (which has a large parking structure), and then hits 150mph on its way to Providence. Local MBTA service hits all of those intermediate stops.

https://www.amtrak.com/routes/acela-train.html

Is that a joke? Not every train stops at every station. And an advantage of high speed trains is they can accelerate very quickly.

> And an advantage of high speed trains is they can accelerate very quickly.

They really can't.

They accelerate reasonably quickly, but doing so any faster uses more energy and also starts impacting passenger comfort. People would like to have a cup of coffee on the table without hot liquid sloshing out onto their laps.

They absolutely can. They're obviously limited by passenger comfort as the other commenter said, but the difference between an Acela and a Northeast Regional in acceleration speed is obvious.