There's been a fascinating and extensive debate over at humantransit.org on competing proposals for how to improve transit along the Broadway corridor in Vancouver, BC. Broadway street is a major east-west thoroughfare through the heart of the city (which is to say not through downtown, as downtown Vancouver is at the city's northern edge, across False Creek), presently served by extremely-crowded bus lines. This is one place where a legit claim can be made that rail is absolutely needed for capacity reasons. The two competing visions for the corridor are a network of surface rail lines, on Broadway and the surrounding streets, presumably running in a dedicated right-of-way; or an westward extension of the Millennium Line of Skytrain. While I lean towards the Skytrain solution, this is a Vancouver issue so my opinion on the matter is neither particularly strong nor particularly relevant.
What becomes apparent from listening to the debate, though, is that the two solutions are designed to serve different needs. Skytrain supporters are interested in comprehensive regional transit; they want to get from UBC to the Canada Line or to Vancouver's eastern suburbs quickly. Surface rail supporters are interested in community-building; they want to improve the quality of their neighborhood. (Similar debates occur in Portland with regard to MAX and the Portland Streetcar--and ironically, the pro-surface-rail proposal sites Portland Streetcar as a model). But not only are the two solutions designed to serve different needs, there's no inherent incompatibility between them. There's no particular reason that Vancouver couldn't extent the Millennium Line all the way out to the University, and build streetcar lines to replace the busiest bus lines.
Except for money.
One big problem with these debates is many of them assume, a priori, a world of limited funding. Of course, that's a valid assumption in most cases (it is the world we live in, after all), but it often has the affect of chilling debate by forcing advocates to stake out either/or positions: In the present instance, its either surface rail down Broadway or SkyTrain; but "both" appears to be out of the question. In Portland, we see calls to postpone or kill the Milwaukie MAX line not because the project lacks merit, but because many would rather use the money for something else they consider more important--such as preserving and extending bus operations. Rather than viewing MAX as an important part of the transit system, it's viewed as a threat to other needs, and vice versa.
But obviously, we cannot pretend that we live in an unlimited-funding universe. There will always be more worthwhile projects to pursue than money to pay for them--and that would remain true even if transit were funded as it ought to be.
Professional planning agencies have to deal with this as part of their jobs--and they have fairly effective methodologies for racking and stacking projects: Rather than taking an either/or point of view, the potential projects that can be done are each considered and ranked. Projects aren't ranked in isolation--in practice, there are far too many interdependencies to do that effectively--but they do specify different funding scenarios, and list which projects have to get done even in a limited funding environment, vs which ones only get done if money falls from trees, vs which ones aren't worthwhile in any case.
The advantages of doing business this way are obvious: For one thing, you don't alienate potential allies quite as quickly. For another, this allows all the needs of a region to be given fair consideration. For a third, if the homework is done properly, and there are high-priority projects which nonetheless can't fit into a limited funding scenario, it gives leaders and activists a stronger case to seek out additional funding. It's hard for an activist to make the case that we need more money to build whatever, when the same activist has been busy denouncing whatever as a ridiculous boondoggle--when he's not really opposed to the project on its own merits; but simply wants to preserve the funding for something else.
[Edited for links and minor additional commentary]