> It's part of the reason why, as much as I love off-road biking, I've become a bit of a skeptic about the rail trail movement. And I'm wondering if it's a good idea to be using these prime rights of way for bike use exclusively -- maybe we need to be promoting the restoration of rail instead or maybe even dual use if possible?

A few things:

1. Rail trails aren't for bike use exclusively. They may be the most visible use, particular on corridors like the Minute Man which has a strong bike commuter community, but they are ultimately multi use. Maybe we need to frame these trails differently from a marketing/PR POV though, since NIMBYs do feel a strong urge to latch onto the "crazy biker mowing down pedestrian" stereotype which is misleading and overblown.
2. I think rail w/a trail is a good model, and I've rather see that, but these ROWs are pretty narrow to support that. Most were double tracked at one point, but ROW has been encroached upon for decades so they tend to end up pretty narrow. Finding 15 feet of space plus some space for greenery and trees is hard enough at points. We can't just throw down a single rail track and call it a day either; we'd need double track sections for safe passing of trains, we'd probably want electric trains for maximum efficiency and headways; we'd want to fix all the at grade crossings if we want safer crossings and faster trains... etc. We could do subway style trains instead, but each mile of subway costs half a billion in the US at best... so for a few miles of transit expansion the State needs to drop several billion (see GLX in Somerville/Medford, a $1 to $2B project depending on what you count). It would be AWESOME if we could actually support transit and multi use pedestrian/cycling infrastructure but I don't see much political support for actual transit improvements beyond token improvements (GLX is good enough for most politicians, now let's spend $10B on highways!!! Even if that makes 0 sense).
3. I think we really need to streamline these things and remove a LOT or maybe ALL of the local input. NIMBYs shouldn't get a dozen community meetings to bitch about every little thing about a project. We've built dozens of rail trails in MA. The State, be it MassDOT, DCR, the MBTA, etc, all know how to handle multi use trails. The Feds have guidelines for this too if we really need a second opinion. We do not need some input from NIMBYs in Belmont who want to be super duper helpful by suggesting a dozen costly improvements that will take years to implement.

> At the very least we need to overcome suburban NIMBYism and to do that we need to resurrect Sylvester Baxter's visionary 1890 plan for Boston to become an integrated metropolis/city-state.

I don't know much or anything about Sylvester Baxter, but I think we just need to start ignoring NIMBYs. We've given them too much political and PR power by broadcasting their vocal minority views. Rail trails are an excellent use of ROW if we're not actually going to build transit. We should take every mile of unused track that the MBTA/MassDOT/local freight companies own and start ripping them out or improving them. There's no need to wait 3 decades to find out if CSX or Pam Am or whoever actually wants that freight line. Take it by eminent domain and build some trails on it. Add a clause for transit and if we ever get serious about dumping tens of billions into the MBTA we'll replace the trails with trains and maybe subways + a trail above or if space permits a commuter rail train + trail.