Subway is certaintly a bit misleading for this network. It certaintly has some elements of subway networks, like downtown tunneling, high level platforms and grade separations for most of the lines (plus naming consistency), but I suppose it would be more akin to the LA Metro A or E lines than a full heavy rail line.
For some small stretches where running along a street is unavoidable, the line would need to utilize a median-running right of way. Specifically, Providence Station to Pawtucket / Central Falls (R1), Federal Hill to North Hartford (R2), and Grace Church to Reservoir (R1) would run at grade along major streets until they rejoin dedicated right of ways.
As for the routings: R1 is basically just the RIPTA R-line – the busiest RIPTA route – extended and converted into a subway, with an extension to TF Green Airport. It serves everything from dense neighborhoods and colleges to the Roger Williams Zoo!
R2 begins as an east-west route from Rhode Island College, serving Olneyville (one of the densest neighborhoods in Providence) before it crosses the R1 line at Providence Station. Then, it utilizes the existing East Rail Tunnel and a restored rail bridge to take the line under Brown University into East Providence. Then, it follows Taunton Ave up to Wampanoag Plaza before heading south towards Bristol.
Normally, I would have ended the line in East Providence, but after much deliberation I realized extending R2 down there would provide better service than building a new RailRhode line. In short, R2 enables more one-seat rides and serve smaller neighborhoods along the route better, uses smaller stations, and would operate at the same speeds as RailRhode line along the same route anyways.