Sunday, May 26, 2013

Oregon's Aging Bridges

There are 7,202 bridges in the State of Oregon (Statemaster Website) and of these, 561 bridges are structurally deficient (Statemaster Website) which means they require significant maintenance and repair to remain in service.  Issues include need of paint to prevent rust, cracked concrete, rutted bridge decks, and
problems with support structure.  These structures will eventually need rehabilitation or replacement to address deficiencies.  Often structurally deficient bridges have posted weight limits to restrict the gross weight of vehicles using the bridges to less than the maximum weight allowed.  1,203 of the states bridges are rated functionally obsolete (Statemaster Website) which means they were built to standards that are not used today and they do not have adequate lane widths, shoulder widths, have low overhead clearance or might occasionally flood. 
Cape Creek Bridge, Lane County 1932
(Photos by James Norman, ODOT)

With about 40% of the state bridges being over 50 years old (OregonLive), issues are beginning to arise with today’s traffic.  Bridge design standards have evolved since the 1950’s and today’s freight loads can be heavier and longer, vehicle speeds are higher resulting in greater impact loading, and there are increases in traffic volume. (ODOT, 2007)  Bridge life expectancies vary based on the design standards that were in place at the time the bridge was built, materials used, environmental and operating conditions, and the maintenance and preservation projects.  Typically the life expectancy of a bridge is 50 to 80 years, but ODOT uses a 100 year life expectancy which assumes that there are adequate levels of routine and preventative maintenance, periodic rehabilitation, and prompt resolution of other problems, such as streambed scour and collision impact damage. (ODOT, 2007) This might not be a reasonable life expectancy for ODOT to use because of the assumptions for maintenance, rehabilitation and prompt problem resolutions.  Older bridges are becoming functionally obsolete as our design standards change, maintenance budgets are diminishing and there has been a dramatic rise in construction cost since 2004. (ODOT, 2007)

Oregon City Bridge, Clackamas County 1922
(Photos by James Norman, ODOT)

Currently, freight mobility is largely dependent on trucks, and our state highway system transports about 76%, or more than 250 million tons, of commodities to destination in and outside of Oregon. (ODOT, 2007)  The Federal Highway Administration (FHWA) predicts that the volume of freight traffic will increase by 70% in the next seven years.  The movement of goods and services is important for the economic benefit of the state and statewide connections are key.  Bridges can be a “weak link” to the transportation system because of concern for load capacity, vertical clearance and deck width.  In order to evaluate capacities and clearances, bridge inspections are necessary and federally required every two years.  They are used to locate and evaluate existing bridge deficiencies and ensure the safety of the traveling public.  But accidents can happen even when bridges pass inspection, as seen recently in the State of Washington with the collapse of the I-5 Bridge over the Skagit River in Mount Vernon.  That bridge was classified as functionally obsolete for current traffic volumes, and was considered “fracture critical” meaning that severe damage to a single girder could cause collapse.  This collapse occurred when an oversize load struck an overhead support beam, sending a section of the bridge and two cars into the river on Thursday evening. (OregonLive)  One of the maintenance considerations for bridges is vertical clearance obstructions.  Requirements for new construction are 17’-6” of clearance, with retrofit requirements at 16’-6” of clearance.  Clearance of 15’ on bridges is defined as deficient or gains a poor rating.  Bridges are considered a special issue because vertical clearance can be eroded when pavement preservation efforts add additional levels of asphalt under structures. 

South Myrtle Creek Bridge, Douglas County  1939
(Photos by James Norman, ODOT)
The State Bridge Program objective is to repair or make rehabilitation improvements to extend life of existing facilities and replace when necessary.  The goals are to improve the performance along freight corridors at critical points, to maximize investment by building bridges that require less maintenance, have a longer life span, and meet future transportation needs.  The Statewide Transportation Improvement Program (STIP) projects are prioritized to concentrate on addressing load capacity and safety issues for Freight Routes and the National Highway System (NHS) routes by allocating sufficient funds for functional and safety needs.  STIP projects focus mainly on maintaining freight mobility and preserving existing bridges that meet specific requirements:  that they are greater than 20’ in length and have not been constructed or had major reconstruction with in the past ten years. (ODOT, 2007

Bridge assets were valued at $2.7 billion in 2005. (ODOT, 2007)  Maintenance timing is important because sufficient rehabilitation projects need to occur at the most cost-effective time in the life cycle of a bridge, assuming there is money available in the budget.  The Oregon Transportation Investment Act (OTIA) III was a ten year bond-funded bridge repair and replacement effort that began in 2003.  It authorized the issue of Highway User Tax Bonds to address the problem of 365 cracked girders on interstate and state highway bridges, at an estimated cost of $1.34 billion. But at the expected level of investment after 2011, bridge conditions will decline again through 2017. (ODOT, 2007)  The replacement schedule should be an average of 27 bridges per year to keep pace with the expected lifespan and prevent the backlog of bridge-needs from continuing to grow. (ODOT, 2007

Hawthorne Bridge, Multnomah County 1910
(Photos by James Norman, ODOT)
If we are to maintain our current level of statewide highway connections and actually have bridges that survive the 100 year life expectancy, we must increase our level of funding that allows for adequate levels of routine and preventative maintenance, periodic rehabilitation, and prompt resolution of other problems, such as streambed scour and collision impact damage, and adjusts for the fluctuation in construction costs.

1 comment:

  1. Great post Tessie about our bridge situation. One of the things that is not often talked about but has been getting more attention lately is how few of our bridges are incapable of withstanding a subduction zone earth quake.

    There is a video from a City Club presentation and one of the panelist stated that only a handful of our bridges will withstand the quake in this state when the Cascadia Subduction Zone goes off. It was mentioned in another article the new Tri-Met bridge may be one of the few and maybe the only bridge that withstand the quake when it happens.

    The Japan earthquake that was not supposed to happen back in 2011 (it just happened that Oregon's top earthquake experts were in Japan for a conference when it happened), has brought new light into this situation. Of course as you it will take money to fix up our bridges and unfortunately there is less and less money to be had. Hopefully we don't have to deal with the worst case scenario to get action on this critical issue.


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