A $7 million project to replace "deficient" guardrails along more than half of the 460-mile Blue Ridge Parkway will get under way Dec. 7.

Mike Molling, chief of maintenance and engineering for the parkway, said the work will begin in the south near milepost 350, about 30 miles north of Asheville, N.C. It will move north to milepost 99, about 20 miles north of Roanoke.

Parkway traffic may be reduced to one lane in some areas as the work is done over the next 600 days, he said.

Molling said he wasn't sure when the existing wooden guardrails were installed, but many are "pretty old. Some of the stuff there in the Roanoke Valley is in terrible shape," he said.

The original guardrails are all-wood. They are incapable of stopping a car moving at 45 mph, and some are too low to the ground to be effective, he said. "They are pretty deficient."

The replacement rails are "crash-worthy up to 45 mph, the general speed limit along the parkway," he said.

They are made of steel-backed timbers and are somewhat higher than the old rails. Visitors who see both types side by side would notice the difference of the sturdier, thicker rails, he said, but they retain the natural wood appearance travelers are used to.

The project was funded out of the National Park Service's special "line-item construction" budget, he said, reserved for larger capital projects and subject to particularly intense scrutiny and competition. This project has been in the planning stages for three years, he said.

No federal stimulus funds are being used.

It will be a while before travelers in the Roanoke region see the work, which is scheduled for completion in May or June of 2011.