Wastelands of Southeastern Massachusetts

So without admitting ownership of any products of a particular company, I was looking at add-ons for Microsoft Train Simulator tonight. Searching train-sim.com for "MBTA" comes up with something purporting to be the T commuter rail between South Station and Providence. I've downloaded this before, and was disappointed; I figured that, since this was "MBTA v5", things might have gotten better. Alas, it's still five pastoral miles from South Station to Back Bay, the branch to the Worcester commuter rail and the Orange Line are completely absent, the signals leaving South Station are all wrong and there's no more signals anywhere else along the line. Oh yes, and leaving Back Bay you make a left turn, and then...nothing. There's tracks all the way to Providence, but looking away from the train saw nothing but green grass all the way to the horizon. Places I know the track layout (of note, around Readville) are also just wrong. For a 100 MB download, I'm a bit confused about what's actually involved here; I don't think even the good Northeast Corridor implementation is that huge.

If I were going to do this sort of thing, I'd do the north-side commuter rail, or at least the Lowell and Haverhill lines. But I don't actually know what tools are available and necessary for building an MSTS layout. I'd be somewhat happier if there were tools (and an MSTS engine) under Linux, but nobody's written one that I've found, and actually doing it looks like Effort.