U.S. Highway 27 and Signal Mountain Road will look like this Lawson Whitaker rendering when work is complete.

Workers install concrete forms before pouring the exterior rock shaped mold as construction continues on the U.S. 27 road widening project.

The Great Walls of Chattanooga are rising.

Commuters into Chattanooga from the north end of the county on workday mornings are greeted by orange barrels and men in hard hats climbing red ladders or dangling in buckets scores of feet above the roadway.

The workers are putting the finishing touches on the first four of 33 walls that will turn the 1.6-mile passage through narrow breaks of Stringer's Ridge into a rock-walled canyon.

The three-year, $102.5 million project will widen U.S. Highway 27.

But before the four-lane road can expand to six lanes, the canyon around it must be widened, too.

And steadied.

Ken Flynn, the regional construction manager for the Tennessee Department of Transportation, said the ridge tops on both sides of the road now carry the additional weight of new condos, homes and apartments.

That continues to add complications to the hundred-million-dollar mile.

"The project is 5 percent behind," Flynn said.

That's not too bad, he said, but it has extended the projected finish date -- now December 2014 -- by two months.

The overweighted ridgetops have required more walls and terracing than anticipated when the project was designed several years ago when the ridgetops had no residents. The original design was revised, bumping up the number of planned walls to 31.

But after the work began early this year, engineers realized they would need still more walls, bringing the number to 33.

In one spot, a terrace of three walls between the most prominent new homes overlooking Chattanooga will tower 120 feet above the roadway. That's the equivalent of a 12-story building.

The tallest single wall in the project is 50 feet -- a five-story building.

Working the high wire

On Tuesday, Efrain Colchado and eight crew members with Wright Bros. Construction stood harnessed to the side of a nearly finished wall as they worked to corral a 1,250 pound concrete form near the top.

A crane held the weight of the form, but the men had to use their own brute strength and to lever and wedge the form over the steel support poles to be welded into place before a concrete "cut-rock face" could be poured and molded.

Above them, Charles Frost, manned the crane he'd had to drive up a nearly vertical slope. Below them, concrete supervisor Mark Jenkins swung a second crane into action to offer additional leverage so the harnessed cowboys could work the oversized jigsaw puzzle.

Frost laughed off questions about driving cranes and earthmovers on slippery dirt of Stringer's zig-zag terrain.

"After you walk up and down this hill two or three times a day, driving these vehicles on them starts to look real easy," he said, patting his thighs.

"This is normal everyday work," Frost said.

Flynn explained that each wall is built from the top down.

First holes are bored -- some 70 feet down. Then steel pylons are lowered into the holes and concreted. As the earth is moved away from the front of the pylons, rebar and a wood face are strung between the steel ribs.

Then comes more concrete, and earth ties -- metal pins and cables driven deep into the slopes to act as giant molly bolts and provide still more strength.

"We want these walls to stay there," Flynn said.

Neighbors and commuters

The work - complete with pounding noise, vibration, dust and massive tree cutting -- has been met with mixed reactions from Chattanoogans.

When the trees began coming down in May, hilltop resident Kathy O'Brien said the noise was rough but her view of Chattanooga was improved.

On Thursday, Lea Brainerd, who lives in a new condo on Riverside Avenue overlooking Manufacturers Road, said progress isn't always easy.

"There's some noise sometimes, and sometimes they have to close the road. But usually it's not bad," she said.

Responding to a Facebook inquiry, Derek Burnett said the roads in Chattanooga "have been horrible for years. I'm all for road improvements in Chattanooga, especially in the downtown area."

The state highway department has received some complaints about noise and vibration, including one from a woman on Houser Street which runs just below the wall work in front of the tallest walls.

After reviewing her concerns, Flynn asked contractors to expedite work on one retaining wall so that it might serve as a buffer to additional work now planned later.

He said residents have been very patient and understanding of the construction.

"Everybody's kind of settled down. They know we're trying to do the best we can not to disturb them any more than we have to," Flynn said.