Highway Safety - A Primer for the public on U.S. Bridge Safety Information

“London Bridge Is Falling Down”

The lyrics from the well-known Mother Goose nursery rhyme talking about bridges falling down, pins and needles bend and break, build it up with wood and clay will wash away, we must build it up again, iron and steel will bend and break and how will we build it up, should give us pause for quiet contemplation about our own home towns’ infrastructure.

The Minnesota bridge collapse that occurred August 1, 2007 brought traffic to a standstill and bridge safety to the forefront of every commuter that drives on this 8-lane Interstate 35W slip of road. Thirteen people died and over 145 were injured in this bridge failure.

Will this be an isolated incident? – A primer on bridges.

Today we present a primer about the Minnesota bridge collapse issues.

16 steel plates were ½ inch thick rather than 1” thick. There are 465 bridges of similar design in the United States.  The National Transportation Safety Board concluded the bridge’s “design” was the flaw. Gusset plates holding together angled steel girders that support the bridge from underneath weren’t thick enough and thus were not strong enough for the intended purpose. Gusset plates are not something about what commuters would notice or have much if any knowledge. While design of the gusset plates is the identified flaw, it raises the question about whether the materials supplied were the correct ones. That conclusion means the plans from the 1960’s bridge weren’t adequate for modern day’s heavy, continuous and voluminous commuter traffic. The bridge was being worked on and PSI Construction re were 578,000 pounds of trucks, equipment and supplies were stockpiled on the bridge.  The 2008 State of Minnesota, Office of the Legislative Auditor, Evaluation Report, State Highway and Bridges.

What are Gusset Plates?

Gusset Plate - A metal plate used to unite multiple structural members of a truss.

All this is well and good but one has to wonder about the number of similarly designed bridges and their locations.

What does it mean when inspectors note a bridge is “fracture critical”?

When a bridge is designated as “fracture critical” it means any failure of the parts will bring down the entire bridge. A list of “Fracture Critical State Highway Bridges”

“Fracture-Critical
A fracture-critical bridge is one that does not contain redundant supporting elements. This means that if those key supports fail, the bridge would be in danger of collapse. This does not mean the bridge is inherently unsafe, only that there is a lack of redundancy in its design.”

“Fracture Critical State Highway Bridges – in California (The list is five pages long.)

Provided below is a list of all fracture critical state highway system bridges. A fracture critical bridge is a steel structure that is designed with little or no load path redundancy. Load path redundancy is a characteristic of the design that allows the bridge to redistribute load to other structural members on the bridge if any one member loses capacity. This designation is a function of the design of the bridge and not the condition. In fact, a brand new bridge can be fracture critical. Caltrans has a fracture critical inspection unit that uses specialized access and non-destructive testing equipment to identify any potential concerns, even those that are not visible to the human eye.”

Where can I read about bridges in my home town, county and state?

You can locate Internet accessible bridge ratings by state and county. For instance in Texas six bridges have been identified in the fracture critical bridge category. So much for pork in Washington flowing back home to Texas.

U.S. Bridge Information

“Bridges and large culverts are designed, constructed, and maintained with the best in professional care by highway agencies throughout the country. Their robust inspection and safety programs meet or exceed all federal requirements.

Except where federal exemptions are granted, states are required to inspect bridges on the National Bridge Inventory at least once every two years.

Highway and bridge safety is taken very seriously by our members.

The American Association of State Highway and Transportation Officials, including the Subcommittee on Public Affairs, has extended its expertise and resources to assist with any needs of investigators, the Minnesota Department of Transportation, and our member states. One of those needs has been credible and trusted public information, which is being addressed through the provision of this Web site.”

Bridge Statistics by State – This site allows you with Google Earth to access information directly and locate the bridges on an aerial map or you can download the PDF formatted map.

The Iowa Department of Transportation has really done a nice job of making available information about Iowa’s bridges. They should really be commended for their transparency. Iowa’s Bridge Inventory described by County, sufficiency rating, year built and year reconstructed.

Bridges in Iowa

“To provide increased access to bridge information, the Iowa DOT has developed a Web program that allows Iowans to pinpoint a state highway bridge in their area using Google Earth software and Iowa DOT data. Information available online now includes the year a bridge was originally constructed and reconstructed, if it has undergone major work, the average daily traffic count, the highway it carries and feature crossed, and its national bridge sufficiency rating.

The bridge sufficiency rating is calculated on scale a of 1 to 100 for the National Bridge Inventory maintained by the Federal Highway Administration, with 100 being the highest. The rating is determined following a complex bridge inspection process, which examines its structural components. Any bridge in Iowa found to be unsafe is removed from service until it can be returned to a safe state of operation or replaced.”

What is a bridge sufficiency rating?

“Structurally Deficient and Sufficiency Rating
A bridge sufficiency rating includes a multitude of factors: inspection results of the structural condition of the bridge, traffic volumes, number of lanes, road widths, clearances, and importance for national security and public use, to name just a few.

The sufficiency rating is calculated per a formula defined in Federal Highway Administration’s Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges. This rating is indicative of a bridge’s sufficiency to remain in service. The formula places 55 percent value on the structural condition of the bridge, 30 percent on its serviceability and obsolescence, and 15 percent on its essentiality to public use.

The point calculation is based on a 0-100 scale and it compares the existing bridge to a new bridge designed to current engineering standards.

The bridge’s sufficiency rating provides an overall measure of the bridge’s condition and is used to determine eligibility for federal funds. Bridges are considered structurally deficient if significant load carrying elements are found to be in poor condition due to deterioration or the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to point of causing intolerable traffic interruptions.

Every bridge constructed goes through a natural deterioration or aging process, although each bridge is unique in the way it ages.

The fact that a bridge is classified under the federal definition as “structurally deficient" does not imply that it is unsafe. A structurally deficient bridge, when left open to traffic, typically requires significant maintenance and repair to remain in service and eventual rehabilitation or replacement to address deficiencies. To remain in service, structurally deficient bridges are often posted with weight limits to restrict the gross weight of vehicles using the bridges to less than the maximum weight typically allowed by statute.

To be eligible for federal aid the following is necessary (a local match is required):

·                            Replacement: bridge must have a sufficiency rating of less than 50 and be either functionally obsolete or structurally deficient.

·                            Repair: bridge must have a sufficiency rating of less than 80 and the jurisdiction is prevented from using any additional federal aid for 10 years. “

What about those bridges in Iowa?

There are several bridges in Iowa rating below 50. Some carry interstate traffic. There are many throughout the country.

Adair County, number 13110, rating is 39, I-80, built in 1958 and never reconstructed.

Adair County, number 13000, rating is 37, IA 92, built in 1958, and reconstructed 1972.

Bremer County, number 15460, rating is 43, US 63, 1956, never reconstructed.

Bremer County, number 15740, rating is 48, IA 93, built in 1936, reconstruction 1960.

Polk County, number 42740, rating is 49, I-235, Des Moines River and RD, built in 1962 and reconstructed in 2007.

This post is already too lengthy and so to catalog all sub-50 sufficiency rated bridges from the 97 pages of the inventory is beyond this post; but you can examine the report and any bridges you cross to see the sufficiency ratings. Where I live in Polk County we have a number of sub-50 sufficiency rated bridges. We’ll save that for another day. For today let us stick with the Minnesota fact investigation because history may indicate what we should expect.

Can I rely on state bridge inspectors?

Adding insult to injury is the finding that State of Minnesota bridge inspectors’ years earlier noted gusset plates bowing and bending but took no affirmative action to correct the problem or to warn the public.

Is Minnesota alone?

California found all steel deck truss “structures” to be safe.  No problems found in Georgia, Florida or South Carolina. Isn’t this what Minnesota state bridge inspectors also reported up through July 31, 2007? You can read a “Condition of U.S. Highway Bridges: 2000 – 2007” at the Engineers News-Record.  Highway Bridges: Conditions and the Federal/State Role. That report concludes our national bridge inventory of 600,000 includes roughly 12% or 74,000 being classified as structurally deficient.

We wrote before about the King Can Do No Wrong; in this case I guess we will find out if that is still true. Highway Safety – Why if it is negligent can’t I sue the State of Iowa?, Steve Lombardi on InjuryBoard explains the sovereign immunity doctrine.

You be the judge. A selection of videos to view.