New concerns about the safety of the nation's bridges are being raised in the wake of yesterday's deadly bridge collapse in Minnesota. Department of Transportation (DOT) statistics show that 160,000, more than a quarter, of the nation's bridges are rated "structurally deficient" or "functionally obsolete," and many don't have proper warning signs restricting weight loads.
The 160,000 bridges rated deficient are not necessarily unsafe, according to DOT, as long as there are restrictions on the types of vehicles, weight or traffic volumes allowed on the bridge.
But a 2006 investigation by the DOT inspector general revealed that one out of every 10 "structurally deficient" highway bridges did not have load ratings that reflected the condition of the structure. In other words, posted signs told drivers the bridge could carry more than it could safely handle.
"In a worst-case scenario, the lack of a correct load rating or the lack of a weight limit posting could allow heavier vehicles to cross and cause severe structural damage or the collapse of a bridge," the report stated.
The interstate highway bridge that collapsed in Minnesota was rated by DOT as "structurally deficient" in 2005, according to the Department of Transportation.
A 2001 state evaluation of the bridge, however, found only preliminary signs of fatigue. Minnesota Gov. Tim Pawlenty said the bridge had been inspected in 2005 and 2006 and no deficiencies were identified. State officials have declined to comment on the apparent disparity between the findings.
The IG's report found fewer safety concerns overall about Minnesota's bridges compared to bridges in other states. By contrast, nearly a quarter of all highway bridges in the state of Rhode Island surveyed in 2003 were "structurally deficient," according to the report. That state had the worst record in the nation. Michigan and Pennsylvania trailed: between 15 and 20 percent of their major bridges had significant cracks or other damage which reduced their weight-bearing capacity, the report said.
California, Delaware and the tiny District of Columbia, however, saw more daily traffic over deteriorating bridges than anywhere else, according to the report. Those three saw more than 50,000 vehicles a day pass over stressed highway bridges in 2004, the last year for which data was available.
The IG's report estimated that as of 2004, Minnesota had some of the highest average daily traffic over structurally deficient NHS bridges in the nation, some 30,000 to 40,000 vehicles a day.
The Minnesota disaster appears to be the worst bridge failing of its kind since the 1995 collapse of the Arroyo Pasajero bridge in California, which took seven lives.
Other notable bridge collapses cited by the Department of Transportation:
1989: Hatchie River Bridge, Tenn. (8 deaths)
1987: Schoharie Creek Bridge, N.Y. (10 deaths)
1983: Mianus River Bridge, Conn. (3 deaths)