The EGE wrote:PVD only has space for four tracks.
I'm fairly sure "TFG" (Providence Airport) is planned 6, and that the garage was built with this in mind. Exactly as it "should have been" at BWI, the plan is for:
2 "Acela bidirectional bypass" at the centerline
2 Amtrak Northeast Regional tracks on the inboard sides of the island platforms
2 Commuter tracks on the outermost sides of the islands.
As you can see in this aerial view from the North/Boston side looking towards New Haven (linked below), the current MBTA bidirectional* platform on the southbound (railroad westbound to NHV/NYC) side is provisioned to become the "southbound island platform" (and the platform is already "done"/ready for this role):
https://goo.gl/maps/QPRzcKRpw1s" onclick="window.open(this.href);return false;
You also see this in the space they've left between the glassed elevator tower and the outer edge of today's platform:
https://goo.gl/maps/G6vJGCP3cky" onclick="window.open(this.href);return false;
In the view above, you see they've left "stutter step" / "knockout" horizontal framing in the garage that would allow them to easily
1) "bore through" on the left to finish today's island platform and add an outermost track without touching the elevator
2) "bore through" on the right to create a northbound island, leaving the vertical elements in the center of the island (as you can already see on the opposite side).
In the second view linked above, you also see how they've positioned the elevator (in the glassed tower) one train's width outboard of the edge of the (future southbound island) platform, and left space to widen today's side platform into tomorrow's full-length, full-width island.
Of course what would a reserved ROW be without a signals box?
In this case, nestled under a horizontal element that could be removed (similar to the ones that area already "not there" on the other view.
*MBTA/RIDOT service is effectively single track south of Providence (downtown).