Jessica Flynn

Tennessee Department of Transportation bridge inspection crews found no problems with overhead road signs in Hamilton County after a sign fell onto an interstate earlier this week.

A cantilever sign — which is supported by a single pole and extends over a couple of highway lanes — collapsed Monday on Interstate 65 South in Franklin, Tenn., causing delays for motorists and a three-car accident, according to Jennifer Flynn, TDOT community relations officer based in Chattanooga. The sign weighed an estimated 15,000 pounds and did not strike any moving vehicles, Ms. Flynn said.

The Franklin sign was 15 years old, Ms. Flynn said, although its life expectancy should be more like 50. Most of Hamilton County’s signs are well under 15 years old, she said.

Across the state, bridge inspection teams are checking the massive metal structures for damage. Crew members are checking that bolts are tightened and they are applying a dye that helps locate small cracks.

TDOT is inspecting all cantilevered highway signs over a 30-day period, Ms. Flynn said. “If there is a problem, we’ll find it,” she said.

She confirmed that one weakened sign already had been identified and replaced Wednesday on Interstate 26 in Kingsport, Tenn.

In Hamilton County, officials originally hoped to inspect 25 structures by the end of the weekend, she said, but a fourth crew joined the original three and the team covered almost all 51 signs in Hamilton County, finding no threat of collapse.

“So far we haven’t had any problems,” Ms. Flynn said.

Most of the cantilever signs are posted along major interstate and state highways, such as Interstates 24 and 75, U.S. Highways 27 and 127 and state Highway 153, Ms. Flynn said. She said Hamilton County has a relatively small amount compared with other metro areas. The Nashville area, for instance, has 242, she said.

TDOT officials attributed the Franklin incident to worn-out metal and said it was possible the continuous exposure to wind and tractor-trailer wind drafts also might have added stress on the sign.

Ms. Flynn showed a picture of the clean break on the Franklin sign, noting the point where the pole ripped off its base and tipped straight forward onto the highway. The large bolts holding the pole’s weight — two of which were relatively new — were all still in place in the photo.

FAST FACTS

* Cantilever: a long, projecting beam or girder fixed at one end, used for bridge construction and supporting balconies, road signs and similar structures

* Weight: Cantilever estimated at 10,000 to 12,000 pounds, plus 800 to 1,000 pounds for signs.

* Number in state: About 650

* Number in Hamilton County: 51

Source: Jennifer Flynn, TDOT; Oxford American Dictionary