The bridge collapse in Washington last week has left many Hawaii residents wondering whether Hawaii's bridges are safe. This is certainly a thought that occurs to many stuck in traffic under an overpass. How safe are Hawaii's bridges?
The bridge that collapsed in Washington is now believed to have collapsed due to a truck accident that struck a critical girder keeping the bridge aloft. "We had a collision between a very heavy vehicle traveling at probably not a small amount of speed crashing into not just one but probably multiple girders, and it failed," Washington Governor Jay Inslee told an afternoon press conference in Mount Vernon.
It is possible to look up bridges on the national bridge inventory database, which is monitored by the federal highway administration. According to the database, the Washington bridge was "functionally obsolete." According to the same database:
"Functional obsolescence is a function of the geometrics of the bridge in relation to the geometrics required by current design standards. While structural deficiencies are generally the result of deterioration of the conditions of the bridge components, functional obsolescence generally results from changing traffic demands on the structure. Facilities, including bridges, are designed to conform to the design standards in place at the time they are designed. Over time, improvements are made to the design requirements. As an example, a bridge designed in the 1930s would have shoulder widths in conformance with the design standards of the 1930s, but current design standards are based on different criteria and require wider bridge shoulders to meet current safety standards. The difference between the required, current-day shoulder width and the 1930s' designed shoulder width represents a deficiency. The magnitude of these types of deficiencies determines whether a bridge is classified as functionally obsolete."
On the other hand, the I-35 bridge that collapsed in Maryland, was categorized as "structurally deficient":
"Structurally deficient bridges are not inherently unsafe. Bridges are considered structurally deficient if significant load-carrying elements are found to be in poor or worse condition due to deterioration and/or damage, or the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to the point of causing intolerable traffic interruptions. That a bridge is deficient does not imply that it is likely to collapse or that it is unsafe. By conducting properly scheduled inspections, unsafe conditions may be identified; if the bridge is determined to be unsafe, the structure must be closed. A 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 often have weight limits that restrict the gross weight of vehicles using the bridges to less than the maximum weight typically allowed by statute."
The Maryland bridge was classified as structurally deficient, and rated a "4" which includes advanced section loss, deterioration, or scour. A bridge rated a "4" is subject to "possible" increased inspection. A bridge is not subject to being shut down until it reaches a 2 which is when a bridge has "advanced deterioration of primary structural elements. Fatigue cracks in steel or shear cracks in concrete may be present or scour may have removed substructure support. Unless closely monitored, it may be necessary to close the bridge until corrective action is taken."
According to the NBI database, Hawaii has a total of 1133 bridges, 143 of which are structurally deficient, and 347 of which are functionally obsolete. This database does not provide the actual rating of Hawaii's bridges, however, which is necessary to know the whole story.
According to Hawaii's DOT, its bridges are safe. But, according to the NBI database, so was the Maryland bridge, and so was the Washington bridge. According to the DOT, it will cost upwards of $1 billion dollars to update and repair Hawaii's obsolete and deficient bridges.