A few days ago I was quoted discussing the so-called high-speed rail project between Chicago and the Twin Cities saying "It's deader."
Peter Bell discussed the many "Near death experiences" of the Central Corridor LRT, which recently got fully funded from the federal government, and is now (almost assuredly, irreversible, as these things go).
Well, of course, in transportation, nothing ever truly dies as long as the line on the map is a memory in the mind of an advocate. A decision to not build a project is easily reversed, since "no" involves no investment in fixed costs, unless something is done in its stead. This is especially a problem if the right-of-way for the facility is being preserved, through either land purchases or prohibitions on development.
Following the lead of John Quiggin, who titled a book "Zombie Economics: How Dead Ideas Still Walk among Us", we might call these old ideas "Zombie Transportation", projects that are now "bad" (or at least no longer "good") ideas, effectively seemingly dead, yet still live in people's minds (and occasionally, like the California HSR, get partial funding before their plug is eventually pulled).
There are lots of other projects one can think of that were lines on maps for decades before being realized. Maryland 200 (the Inter-County Connector), Minnesota 610 are two that come immediately to mind, on the map for 60 and at least 40 years respectively.
In many cases, the problem is simple, ruthless, benefit/cost analysis, the B/C ratio, which may have once been above 1.0, falls to a lower level due to changed circumstances, increased costs due to environmental or other concerns, or a change in demand associated with different finance (tax to toll) mechanism or price of energy. Yet because it is a "commitment" (political, or moral) to a community that their turn will come, they too will get their line built, the line on the map never comes off the map.
Once a project is completed and open, it is essentially irreversible, it will almost never be shuttered before it physically fails (a few exceptions to be noted: e.g. collapsing urban freeways in San Francisco), or requires replacement (Streetcars in many US cities). And even then, many facilities which should be shuttered continue to be maintained and operated, and later reconstructed instead. The difficulty with gravelization is an extreme example of this.
We need a better system for truly killing bad or obsolete ideas in transportation, for culling the losers or the no longer winners. Otherwise, agencies will look at decade old maps, say to themselves: "what remains unfinished", and proceed along to build zombie facilities despite newer priorities rising to the fore and old ideas ceasing to be effective.