Metro Atlanta’s transportation special purpose local option sales tax (TSPLOST) is in trouble, mainly due to the list of projects it proposes to fund. But there is still time to save it.

Local elected officials in the region are starting to question the list — such as Sandy Springs Mayor Eva Galambos, whose Atlanta Journal-Constitution column last week opposing inclusion of the Beltline — and they will have a major influence on regional voters’ ultimate opinion.

The early polls suggesting a slight margin in favor of the TSPLOST, at this point, merely reflect voters’ belief that “something must be done about transportation” rather than specifically “this is what should be done.” And while the city of Atlanta is the core of the region, most of the votes will be cast not in Atlanta and DeKalb County, but in north Fulton and the surrounding counties. Indeed, the population of Atlanta plus DeKalb plus South Fulton is less than one-third of the 10-county TSPLOST region. The list of projects has to be one that serves and appeals to the region as a whole, not just the core.

Here’s the problem: It is not at all clear that these are the highest-priority transportation projects — i.e., the best buys to reduce congestion and improve our ability to move around metro Atlanta.

Some might say that it’s all a matter of opinion — that one person’s priority is another person’s poison — but that’s not true. It’s possible to estimate the number of trips/users each project will enable. In fact, in most if not all cases, the Atlanta Regional Commission already has those figures. You can then divide by the dollar cost of the project and determine the best way to spend our $6 billion.

The problem is those calculations have not become part of the public debate. The good news is that there is still time to revise the list and save the TSPLOST. The transportation roundtable (21 elected officials from around metro Atlanta) have until Oct. 15 to produce the “final-final” list, and that deadline, like the date of the referendum, could no doubt still be changed during the 2012 legislative session.

What should happen is that the entire original project list (about four times the length of the “final” list now in circulation) should be ranked from top to bottom according to trips per dollar, and published as such — no set-asides or quotas, all projects ranked against each other. Then, the transportation roundtable should revise the final list, and should require themselves to pick only projects in, say, the top one-third of the list in terms of congestion improvement — i.e., trips per dollar spent.

This wouldn’t solve all the arguments. In particular, there may still be disagreements about trip estimates, and perhaps about cost as well. But that can be vetted in public, as it should be.

I have no idea what the results would look like, though I’d guess that there would be more road improvements and more bus transit, and less heavy rail transit. But the chips should fall where they may.

The purpose of this SPLOST is to reduce congestion and improve mobility in Metro Atlanta, not to build any specific project. We can’t fund everything that everyone may want; therefore it’s important to set priorities — and set them with a strong dose of analysis about which projects will reduce congestion the most. Let facts rule, not politics.

Bob Irvin of Buckhead is former Georgia House minority leader.