>They're going to have to lay down new rail without grade crossings anyway if it were ever to be built.

See, there's my point, why is it that any time it's mentioned that efficient reliable passenger service isn't completely impossible someone always has to assume that the idea is to do it with absolutely zero upgrades to existing infrastructure?

The railroad corridor between Boston, Nashua, Manchester and Concord used to carry the bulk of the passenger service between Boston and Montreal (before the Northern Line was abandoned). It's not like this is a windy old spur to a mine we're talking about, 100 years ago this route carried all of what I-93 carries today.

I also think it's a bit of a stretch to say that the I-93 corridor between Concord and Manchester as well as the Everett Turnpike corridor between Manchester and Nashua is "sparsely populated".

Then there's the whole aspect of that you're the one saying HSR, I just said passenger rail. The MBTA runs over 100mph on one of their lines using standard commuter rail equipment.