If Georgia is to absorb a projected 4 million more people over the next 25 years, we’ll need a lot of them to make their homes outside metro Atlanta, as I wrote in this space Thursday.

But even if less than half the newcomers end up in metro Atlanta — heck, if not another soul relocates here — some changes are in order for a population that has long outpaced its infrastructure. Ambitious leaders need to think not only about ways to grow the rest of the state, but about how we’ll maintain our quality of life around Atlanta.

That starts with transportation. And one big obstacle we face is that decades of growth have consumed much of the open real estate that might have provided right-of-way for road or rail.

So we’ll have to get a little creative. In that spirit, here are a few ideas. Even if none is feasible, maybe they’ll spur the experts to think from a different angle.

First, the proposed MARTA extension up Ga. 400. The transit agency has studied, and heard residents’ opinions about, which side of the highway new tracks ought to go. Trouble is, the state DOT plans to build tolled express lanes up the same stretch of highway. So there’ll have to be new construction on both sides, to residents’ chagrin.

But that’s also an opportunity. MARTA is still considering bus-rapid transit on 400. If the agency ran BRT on the toll lanes, it might then put its own construction funds toward bus-only lanes from the highway to the various city centers in the 400 corridor.

That would allow commuters to leave the North Springs rail station on an express bus that takes them well off the highway and closer to home. Surely that’s a greater value proposition than asking them to fight through the same traffic to a new train station that they now face getting to 400.

Next, traveling east-west through the northern suburbs can be a real bear. The development from I-75 across east Cobb, north Fulton and northwest Gwinnett to I-85 is so thick, any new infrastructure appears impossible or hopelessly expensive.

But there’s a corridor that runs from Marietta across to Sandy Springs, Norcross, and even Lawrenceville, and it’s mostly clear-cut — a miracle in that area. It’s a corridor for power transmission lines.

Now, before you call me crazy for wanting to put a train (no road wide enough to be worthwhile would fit) beneath 500-kilovolt power lines, do me a favor. The next time you’re sitting in traffic on a busy road, look up. In many places, you’ll see lines carrying 230 kilovolts. That’s enough power to fry anyone, yet we drive under them all the time.

Finally, the downtown connector is a mess. Parallel routes for 75 and 85 were killed long ago, and the only alternative discussed is a tunnel from 400, beneath Morningside and other neighborhoods, to I-675.

Instead, how about going just west of downtown and building an elevated 75 bypass above U.S. 41? It’s about 11 miles from where 41 crosses 75, just before the north end of the connector, down to Cleveland Avenue, just past the south 75/85 split. That’s less than half the distance of the mostly elevated toll lanes being built in the 75/575 corridor. And it mostly spans commercial and retail districts, not residential.

Again, laugh at these ideas if you want. But we’re far enough behind the curve that it’ll take some ingenuity to get us really moving again.