Originally Posted by tvketchum
Bridge ratings cover far more than just structural concerns. Obsolete design factors, such as lane widths, no shoulders, designed capacity versus actual traffic volume, ramp proximity to the bridge, all contribute.
This is all true. And the bridge DOES predate the Interstate highway system. Construction was started in 1940 (!), it was dedicated in 1951 as the WWII Memorial Bridge, and it went into service in 1952 as part of US-90. Interesting tidbit, way back when it was first grandfathered into the Interstate Highway System during the Eisenhower administration, the US Department of Transportation had already
promised to replace the bridge as a condition of taking it over.
Tired of waiting over 40 years for the Federal Government to make good on its promise to replace the bridge, LA-DOTD commissioned a study in 1999 (when the bridge had an overall NBI rating of "4" and a structural sufficiency rating of 40.5%— the drop from 40.5% to 9.9% all happened in the last 20 years, partly due to hurricane Rita in 2005). The study was completed in 2002 and said the cost to replace the bridge would be $450 million. If Hurricane Rita had been just a tiny
bit more destructive, the bridge would have been replaced already same as other bridges destroyed by hurricanes father east on the Gulf Coast. But Rita spared the bridge, and it has entered advanced decrepitude at an ever-increasing rate.
The bridge has a sufficiency rating of 9.9% based on present usage versus design according to the US Department of Transportation, and it has an overall rating of 3 on the Federal Highway Administration's National Bridge Inventory, which classifies the bridge as "Structurally Deficient."* It had an overall NBI rating of "4" way back in 1992— with a structural sufficiency rating of 50%— and has only gotten worse since then. However, the Louisiana Department of Transportation and Development has declared the bridge to be "Safe" using their own standards— which tacitly means "We can't afford to replace it until it falls down so we'll keep slapping Band-Aids on it until then." A whopping 29% (!) of the 13,050 bridges in Louisiana have an NBI rating between "2" and "4" so I put very little faith in the LA-DOTD standards.
*The NBI classifies every bridge on a Federal highway on a scale of 0 to 9.
"0" means closed to all traffic.
"1" is not used.
"2" means obsolete and needs to be replaced.
"3" means structurally deficient and needs major repairs.
"4" is the lowest rating that allows a bridge to be left in place "as-is" though it requires an aggressive routine maintenance program.
"6" is the lowest rating that meets minimum
allowable design criteria.
"8" means that it meets all present desirable design criteria.
"9" means that it exceeds present desirable design criteria.
For the Calcasieu River Bridge, superstructure is rated "3," substructure (foundation) is rated "3", and roadway surface is rated "4," for an overall rating of "3" (averages are all rounded down in NBI).
For comparison, the I-35W Bridge that collapsed in 2007 has a structural sufficiency rating of 50% right up until the time of its collapse, and an NBI rating of "7." A bridge's structural sufficiency doesn't drop all the way to 0% until the moment of its collapse, because any bridge that is still standing has a structural sufficiency of at least 1%. So the I-35W bridge went from structural sufficiency 50% and NBI rating "7" to structural sufficiency 0% and an NBI rating of "0" in less than a minute when it fell.
By the way, the National Bridge Inventory considers the Calcasieu River Bridge to be the 7th
worst bridge in the United States that hasn't yet been closed to traffic.
Over 50,000 vehicles per day cross the Lake Charles Bridge without problems other than slowdowns and fender-benders. Mine won't be one of them. Y'all make up your own minds.