ATLANTA -- If part of Atlanta's traffic future is in a double decker tunnel, we're in for a ride. To see for myself last week, I stepped into a tiny cage with photographer Tracy Reeves for a trip down into the underground tunnel Atlanta is already building for storm and waste water. The yellow "manlift" swayed over the lip of a wide concrete hole, and swung us perilously down 160 feet to a slippery, wet tunnel bed. Engineers looked up in delight as we penetrated their workspace, proud to show off their mastery of the ground underneath Storza Woods in Piedmont Park, and stretching west to Marietta Street.

It looked just like the granite you see along the MARTA walls at the Peachtree Center station. Vivid, black and white streaks etch the edges of the cut. Any interior designer would appreciate the graphic effect. Plugging the hole, a 27 foot drill face sat waiting for its next assignment. The drill just finished eating 8 miles of high-quality granite, leaving an empty tube 27 feet wide for Atlanta's sewer overflows and storm water to rush in to when it rains. How fast does this drill-worm turn? When all goes well, nine feet an hour, say the engineers working for the city of Atlanta. They led me, Tracy and anchor John Pruitt past a nest of cables and air ducts into the dark heart of the tunnel. It was cool, and even in the fragile light of a wall lamp, very impressive.

Why is this a good idea for traffic? Three or four drills this size, working at once, could easily create a tunnel wide enough for cars to drive beneath the surface. Easily, but not inexpensively. The granite is good for this kind of tunnel, and recent engineering advances in boring equipment mean it's easier than it used to be, when blasting was the preferred method to build a tunnel. The engineers in charge say neighbors worried about a tunnel underneath their homes have told them they're pleased and amazed at how little turmoil they're feeling in their houses.

The plan to build a traffic tunnel, begun by a Robert Poole with a West Coast think tank called The Reason Foundation and found on their web site www.reason.org has a high-level sponsor in Georgia. David Doss, a thoughtful businessman from Rome, is the former chairman of the state Department of Transportation. His proposal, called The Big Idea, includes many projects for improving transportation across the state. But easily the most eyecatching idea is this tunnel. As Doss proposes it, it would run underground from Georgia 400 at Interstate 85, burrowing beneath Ansley or Morningside for five miles. Then it would emerge near the Carter Center, to give traffic an exit to downtown Atlanta. For a few miles this proposed toll road would run along the surface, somewhere around Littel Five Points toward Interstate 20, and then dive again, for a three mile long tunnel, to the intersection of Interstate 675 and Interstate 285.

"A double decker tunnel, with three lanes going north, and 3 going south," is Doss's idea. And while everyone who thinks about this for a few minutes agrees something has to happen with Atlanta's traffic, vehement opponents are emerging to the tunnel idea.

Environmentalists in the Sierra Club argue against expanding automobile trips, whether in a tunnel or expanding the interstate system above ground. They'd prefer spending the billions a tunnel would require on systems to get people out of their cars. It's the "if they build it they will come" theory, in reverse. If we don't build it, they can't come. "Atlanta has always tried to solve congestion by building more roads. Adding more lanes as the solution to congestion is the same as saying buying bigger pants is the solution to obesity. At the end of the day, it doesn't make sense, " says Anna Cherry with the Sierra Club.

Other traffic planners, including designers with the Atlanta Regional Commission, think a tunnel could easily soak up all the money for any other improvements. They'd prefer a combination of projects providing more relief in more places. A little of this, a little of that. Not as easy to grasp as a tunnel, nor as exciting. But they believe with today's politics, it is more likely to cobble together support for a list than a single idea.

One bold thinker, Engineer Michael Meyer at Georgia Tech, muses that if money were no object, a tunnel combined with the Beltline idea within Atlanta might be a great combination: Innovative, exciting and capable of stimulating a real debate about how we want to live in the future.

John Pruitt was deeply engaged with Engineer Mike Robison, poking at the smooth bore of the tunnel and peering around the equipment that created it. Tracy Reeves used the eerie light reflecting from the granite to great effect, showing how it feels to be encased in a tube of stone. I was surprised and delighted at the airy feeling I had not expected. Perhaps it was the air pressure, but I found myself wondering Atlanta could hold a fundraising skateboarding competition, or a graffiti contest before they close up this place. Eight miles of beautiful granite walls soon to be covered with sewage. Imagine! The water under my feet reminded me we were touring a marvel that will be unlikely to have many more tourists. Once the storm and waste water starts to flow, this place will hold smelly sewage, and nobody will want to go below, or likely be able to. Atlanta watershed management leader Janet Ward led me toward the shaft of daylight, and I turned back to get a good last look. The drill is coming out to go dig another tunnel somewhere else. The workers were smiling, clearly proud of their handiwork. And the clear answers to Atlanta's traffic problems were nowhere in sight.