Five of Tennessee’s 20 high-traffic, structurally deficient bridges are in Chattanooga, and four of them are downtown, according to an Associated Press analysis of recently released bridge inspection reports in the National Bridge Inventory.
Fifth on the state’s list of most-traveled structurally deficient bridges is the eastbound Interstate 24 ramp leading into Chattanooga to U.S. 127, state records show.
The bridge carries 116,160 vehicles a day, according to state figures.
“Just because a bridge is classified structurally deficient doesn’t mean it’s not safe,” said Paul Degges, Tennessee Department of Transportation chief engineer. “There are 237 structurally deficient bridges in the state, and it would cost $1.75 billion to replace them all. From a management standpoint, we don’t need to replace them all.”
The other local bridges listed on the state’s most heavily traveled deficient bridges list are Interstate 75 over Big Spring Creek; U.S. 27 over West 19th Street; U.S. 27 over West 12th Street, northbound lane; and U.S. 27 over West 12th Street, southbound lane.
Mr. Degges said there are plans, as yet not finalized or funded, to widen U.S. 27, and repair work for the I-24 bridge ramp and the three other downtown U.S. 27 bridges are likely to be included in that project.
Should the bridge conditions worsen, state officials will provide needed repairs before the widening work, he said.
TDOT spokeswoman Julie Oaks said state road engineers are evaluating whether to repair or replace the I-24 and U.S. 27 bridge ramp into Chattanooga when the widening work is done.
“The main problem with this bridge (the ramp) is that the concrete deck has deteriorated to poor condition,” Ms. Oaks said. “Otherwise, the bridge is mostly OK. It is safe to cross this bridge, since the deck deterioration is not yet bad enough to cause any structural problems.”
The bridge last was inspected in September 2006, she said. It is scheduled for reinspection this September.
The three other U.S. 27 bridges over 19th Street and West 12th Street are “programmed” for repair in the fall, Ms. Oaks said.
Those downtown spans carry 68,800 to 77,940 vehicles daily. The I-75 bridge carries 109,090 vehicles daily, state records show.
Mr. Degges said even if the concrete on the decking of a bridge is so deteriorated it makes a hole in the bridge, reinforcement rebar will support the bridge and travelers. The conditions may be hard on vehicles, but the bridges are safe, he said.
The Associated Press sorted the state’s structurally deficient bridges listed on the National Bridge Inventory by average daily travel. The analysis found that among the 20 busiest bridges with poor inspections, six are in Davidson County, six are in Knox County, five are in Hamilton County, two are in Shelby County and one is in Cheatham County.
Hamilton County’s I-24 to U.S. 27 bridge ranks as the fifth busiest deficient bridge in the state. The I-75 bridge ranks seventh. The other Hamilton County bridges rank 17th, 18th and 19th.
Altogether, Hamilton County has 14 structurally deficient bridges maintained by the state, according to the National Bridge Inventory. The inventory is compiled by the Federal Highway Administration from federally mandated reports prepared by state highway departments nationwide.
Of the 19,569 bridges in Tennessee, 8,150 are maintained by the Tennessee Department of Transportation. The remaining bridges are owned and maintained by cities, counties and federal agencies.
A national report released earlier this week by the American Association of State Highway and Transportation Officials, a safety and trade group, ranked Tennessee among the best in bridge maintenance. Tennessee has the sixth-lowest percentage of structurally deficient bridges in the nation, but also has the 10th largest number of bridges.
The national report, released to coincide with today’s anniversary of the Minneapolis I-35 bridge collapse, states the nation’s bridges are safe, but one in four needs to be modernized or repaired — at an estimated cost of at least $140 billion.
The Minneapolis bridge, which carried Interstate 35 West over the Mississippi River, collapsed during the evening rush hour on Aug. 1, 2007, killing 13 people and injuring 145.
A National Transportation Safety Board analysis of that collapse, made public this week, shows that a break in a key steel part includes an area that was rusted on a steel plate that should have been thicker.
An interim report by an NTSB metallurgist states the path of the break on the undersized “gusset plates” went through a corroded area. But the report also indicates the rust may not have caused the break.
Gusset plates are steel sheets used in pairs to sandwich together bridge girders.
Soon after the collapse, the NTSB said the structure had a serious design flaw: 16 of its 220 gusset plates were only half an inch thick when they should have been an inch thick.
Shortly after the Minneapolis bridge collapse and NTSB’s concern about gusset plates and torn rivets on those plates, Tennessee Department of Transportation officials confirmed that Hamilton County and the surrounding southeast Tennessee counties have 46 bridges with rivets.
Among them are the newly refurbished Market Street Bridge and two McCallie Avenue bridges over Dodds Avenue and Willow Street, highway officials said, adding that rivets were phased out of bridge construction in Tennessee in the 1960s.
On Thursday, TDOT’s Mr. Degges said those and other bridges in the region are safe, but he said the cost of bridge maintenance is growing.
“Today, we’re spending $116 million on bridges, and I would say we are falling behind,” he said. “We have a strong program in Tennessee, but the cost is rising so much I don’t think that level of funding is going to keep up.”
The Associated Press and the New York Times contributed to this story.
