You’re doing it wrong, Cobb.

A proposed $500 million bus rapid transit line from Kennesaw to Cumberland would, by the county's own admission, leave traffic congestion as bad or worse a quarter century from now than if it weren't built. The acknowledgment came in an environmental study prepared for a federal grant application and reported last week by The Atlanta Journal-Constitution's Dan Klepal.

Folks in Cobb were already skeptical about the project plan when they thought it was only expensive. Now that it's projected to be expensive and ineffective, don't expect attitudes toward it to soften.

Nor are taxpayers likely to buy the argument more traffic congestion is good because it would boost BRT ridership by making it even more miserable to commute by car. The point, remember, is not to create a successful bus line but to improve mobility.

But just you try to convince Cobb’s top leaders of that point. For years, I have heard (and Klepal’s story underscored) that the goal they and some of their predecessors have set for a transit line on Cobb Parkway is not alleviating traffic, but spurring redevelopment along a major thoroughfare that isn’t exactly a picture-perfect Main Street U.S.A.

Not that Cobb doesn’t have those kinds of places. The downtowns of Smyrna, Marietta and Kennesaw have charm as well as commerce. Smyrna and Marietta in particular are ahead of other metro Atlanta suburbs only now trying to turn their downtowns into live-work-play destinations.

But Cobb’s BRT line wouldn’t link those places; it’d essentially hope to duplicate their efforts along a long, parallel corridor already choked with traffic.

(You know what does link those places, and other spots from Chattanooga to downtown Atlanta? The railroad tracks CSX leases from the state of Georgia, in an arrangement due for renegotiation within the next few years …)

It is an unfortunate, but apparently near-universal, impulse among elected officials and planners to use transportation dollars to steer development where they want it to be, rather than facilitating travel between places people already want to go.

You might think leaders in bright-red Cobb, of all places, would be more inclined to let infrastructure decisions follow and support the decisions residents and businesses -- a.k.a. “the market” -- have made about where they’d prefer to be.

You might think they’d recognize that Cobb’s suburban landscape will always be overwhelmingly car-dependent, and that transit alternatives probably won’t be a net gain for the county if they make it even harder to get around by car.

And you’d better hope that leaders in other parts of the region, those places with downtown dreams, are paying attention. That they’re looking for ways to create local versions of the Beltline, which connects neighborhoods without interfering with cars. That they recognize the best infrastructure we have, at least in the northern part of metro Atlanta, is for north-south trips toward the urban core, even as commuters increasingly need to go east-west between faster-growing suburbs.

That’s where opportunity lies for transit to be a true complement to car travel rather than an unnecessary competitor. But to seize it, we have to be more focused on mobility than obsessed with the mode.