There’s a still-foggy notion wafting around that a “Plan B” will somehow arise from somewhere if voters send the penny transportation sales tax down to defeat on July 31.

That belief, in our view, is too freighted with risk to our economy and quality of life to warrant serious consideration as public debate continues over how best to begin detangling this region’s traffic mess.

The latest group to lobby for Plan B is an unlikely one. The Georgia Sierra Club’s recently announced opposition to the sales tax has proved the biggest surprise yet in the ongoing battle to sway public opinion. The club’s position brings to mind the unfortunate outcomes that can arise when the desire for perfection becomes the enemy of the good, or even the average.

Sierra Club members are not alone in their belief that the penny referendum is so flawed that it should be rejected. Limited-government proponents and anti-transit forces have led this cry up to now, although they oppose the tax for different reasons.

The Sierra Club’s stance is based heavily on the belief that too little of the tax proceeds would be devoted to transit work. They argue that a project mix allocating a roughly equal amount of dollars to road expansion and transit won’t do nearly enough to give Atlantans travel alternatives beyond what sits in their garages.

Do they have a point? Sure. In an ideal world, Atlanta would have decades ago built out a far-flung network of toll roads, commuter trains and even bus rapid transit.

We didn’t. So now, it’s time to view the transportation special purpose local option sales tax, or T-SPLOST, for just what it is: a hard-won attempt by a state ranked 49th in transportation investment to begin making a down payment on billions of dollars in needed work that’s already been deferred far too long.

To argue, for example, that reworking the tangled intersection of I-285 and Ga. 400 is a poor choice is as illogical as saying that any transit project is nothing more than a waste of taxpayer money.

Is the referendum and its project list perfect? No, far from it. Is it workable and, on balance, an improvement over a do-nothing status quo? Yes.

Actively campaigning against the only potential solution proffered does nothing to move metro Atlanta, however incrementally, toward easier commutes. Given that transportation progress in this state moves in the lurching manner of a new motorist learning to drive a stick-shift jalopy, we’d argue there’s too much risk inherent in forcing the defeat of the T-SPLOST in hopes of generating something better.

We believe skittish lawmakers on this one — there is no Plan B. At least not one that would come together anywhere near quickly enough if the sales tax failed. There are too many conflicting interests and viewpoints for any feasible alternative to coalesce anytime soon.

We’d likely be left with what we know too well — doing next to nothing. That will merely pave our way toward stagnation and certain decline as other regions do just what U.S. Transportation Secretary Ray LaHood suspects Georgians have not done — get their act together.

That’s not a road we want to travel.

Andre Jackson, for the Editorial Board