Councilor Dave Marshall is trying to rally support for a streetcar line in Portland, Maine. I've written about this possibility previously, here, and I think it would be great to see it happen someday.
But not quite yet. Portland's regional bus network is woefully inadequate and we need to improve that system first before we talk about spending tens of millions of dollars on a single transit line that only serves a couple of select neighborhoods. Our city needs bus routes to Brunswick and Gorham a lot more than we need a streetcar to Woodford's Corner.
From the other Portland, where they've sunk a lot of money in light rail and streetcar lines, here are five arguments for building cheaper "bus rapid transit" routes — dedicated streets for buses — before we build streetcars and light rail:
Topology advantages. One thing that BRT does easily but rail cannot do is operate in an "open" configuration--meaning vehicles travel in a transitway for part of their journey, and then filter out into the existing street network without need for any special off-transitway infrastructure. Trains can only run where there are tracks and switches, but busses can mix between a busway and local operation.
Partial operation: The ability of busses to run on ordinary streets has a second set of advantages. It permits easier phasing--agencies building a busway or bus lane can open half of it when it's done, and have busses run in the completed sections of the busway and on local streets the rest of the way, and then shift additional sections of the route into the busway when it completes.
Costs. For Class C/C+ operation [in mixed traffic, similar to most streetcars]; bus is way cheaper to install--it's just ordinarily local bus service, possibly with changes to traffic signals and nicer stations. The equivalent rail technology is mixed-traffic streetcar. Streetcar may be better suited to placemaking and land-use transformations, but the performance characteristics of mixed-traffic streetcar are generally the same as ordinary bus service; but streetcar requires installation of tracks. BRT also lets you do class B [dedicated lanes for buses, similar to most light rail lines] cheaply--if planners are willing to take a traffic lane.
Less prone to catastrophic failure. BRT doesn't break down as easily or as spectacularly when the line gets blocked or closed. This benefit is most often discussed in the context of streetcars vs local bus (where obstacles along the route are plenty), but even [rapid-transit rail] lines are impacted by events such as accidents, breakdowns, power or control failures, and maintenance of the right of way. With a BRT, vehicles can simply navigate around, leaving the transitway if necessary.
The ability to pass. BRT makes it far easier to mix express and local services and provide skip-stop service. Busses can simply pull out of the busway for stops; only a little more pavement and real estate is needed to enable passing.
Here in this Portland, the streetcar concept is being promoted by nostalgic railfans whose love for trains obscures these more practical concerns. Some of our local rail advocates actually actively protest against expanding the region's bus system because they see it as a threat against their beloved choo-choos.
Unfortunately, as long as transit advocacy is dominated by these train-first fundamentalists, I doubt we'll see much progress of any kind.