The American Society of Civil Engineers (ASCE) states the United States owns 607,380 bridges. But 11 percent of them — one out of every nine — are structurally deficient. Each day people in the largest 102 metropolitan city regions make 200 million trips over these bridges that are in serious need of repair. The ASCE predicts the deteriorating nature of our transportation infrastructure will reduce our Gross Domestic Product (GDP) perhaps as much as $897 billion by 2020. That said, we are making some headway. The average age of our nation’s bridges has decreased, from 43 years in 2009 to 42 years today. But there is still a long way to go. The Federal Highway Administration (FHWA) states that 30 percent of our bridges have exceeded their 50-year design life — bridges in metropolitan areas deteriorating faster than rural ones due to the increased amount of traffic.
To eliminate the backlog of “deficient bridges” (the total of structurally deficient and functionally obsolete bridges) by 2028 we would need to invest $20.5 billion per year. Currently, $12.8 billion is being spent from all fund sources. So the need to repair or replace bridges poses a huge problem at a time when governments are struggling financially.
How bridges are rated
Tom DeHaven, the executive vice president of operations for Figg Bridge Inspection, St. Paul, Minn., says the National Bridge Inspection Standard requires that bridges be inspected every two years — the result of federal legislation enacted in 1969. The teams that perform these inspections are trained and certified to do the work, but the team leader is always a structural engineer.
Local Departments of Transportation (DOTs) perform most of the inspections, but they often employ consulting engineering firms such as Figg to inspect bridges with specialized technical construction systems like segmental or cable stay. Contracts for these types of inspection services typically run for several years.
During the inspection process, engineers and inspectors look for signs of corrosion and rust, frozen bearings, scaled concrete, cracking, driving surface problems, and electrical problems. But repair priorities are set by DOTs based on fund allotments for doing repair work. So they might shift allocated funds to repaint a bridge to one requiring the repair of exposed, corroded reinforcing before that issue becomes critical.
Rehab verses preventative
If DOTs had all the money they wanted, most of it would go for new construction and preventative maintenance. However, in our real world, significant funding must go for rehab work to repair bridges rated as structurally deficient. Performing these structural repairs is challenging work for contractors as well as the specified products used in the repairs.
Nancy Daubenberger, state bridge engineer for the MnDOT Bridge Office, St. Paul, Minn., says her office currently spends 78 percent of its bridge construction budget each year for new bridge and replacement construction, 7 percent for rehab work on bridges, and 15 percent for preventative maintenance. When MnDOT builds a new bridge, it bases the type of construction on the need of the location, but its requirement now is a minimum 50-year service life. She adds MnDOT is beginning to require 100-year service lives for more important bridges — the I-35W bridge reconstruction replacing the one that collapsed in 2007 being an example. “But we know that doing preventative work yields an even longer life,” she adds.
Dave Juntunen, a Bridge Development Engineer with the Michigan DOT, Lansing, Mich., says his office’s strategy changed in 1998, the year it decided to fund more preventative maintenance. The office did so hoping the commitment would slow bridge deterioration rates and reduce the amount of funding needed for structurally deficient bridge work over time. He says in 1998, Michigan was judged to be near the bottom of all DOTs in terms of needed repair work, with over 20 percent of its bridges classified as structurally deficient. So the state DOT dedicated itself to sound asset management and decided to spend 18 to 20 percent of its budget each year on preventative maintenance. The strategy worked — currently 94 percent of Michigan bridges are rated in good or fair condition.