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.