Minnesota Department of Transportation

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State Aid for Local Transportation

E-Scene April 2024

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Local historic bridges - Phase IV

By: Rachel Broughton, Federal Aid Agreement & Special Programs Engineer

Phase IV of the Local Historic Bridge Study has been completed through a contract with LHB and coordination with MnDOT’s Bridge Office, Cultural Resources Unit, State Aid, and local historic bridge owners.

In the previous phases of this study each locally owned historic bridge was visited, and individual bridge reports were prepared which detailed each structure’s condition, recommendations for preservation, and an estimate of associated costs for preservation. These studies were completed in 2013, 2014, and 2016.
The previous estimates are now up to 10 years old. The Phase IV Study refreshed these estimates in order to understand the current funding needs for the local historic bridge inventory. While the most accurate way to accomplish this would be to re-visit each bridge and prepare an updated cost estimate, this level of effort could not be accommodated within the budget of the Phase IV Study. Instead, eight bridges were selected to be visited and their estimates updated to understand how the costs and scope have changed over time. This data, along with data collected from bridges that have been rehabilitated or re-studied since the original study, was analyzed to further identify trends in cost and condition changes. It was found that general construction material and labor costs have increased 6 percent annually for new bridges constructed on local system in Minnesota since 2013. However, for historic bridge rehabilitation due to the specialized nature of the work and the continued deterioration and increase of rehabilitation scope along with increases in cost due to refinement of scope with detailed studies, the average annual cost increase was found to be 13 percent.

The overall funding needs following the original studies (estimated in 2013, 2014, and 2016 dollars) was roughly $123 million with $64.5 million having been invested in rehabilitation of local historic bridges after the completion of the previous studies. These costs were projected forward to 2023 dollars using the average 13 percent annual increase along with additional controls to ensure individual bridges were not being over inflated. The resulting 2023 funding needs for the local historic bridge inventory is a little over $180 million. This projection is most useful for understanding the needs of the entire inventory because it is based on averages and will be less accurate on an individual bridge basis. However, any local historic bridge owner who is planning a rehabilitation project for their bridge is encouraged to contact MnDOT State Aid to discuss the current cost estimate for their structure. This information will be helpful in planning and scoping, but in order to get the most accurate assessment of an individual structure’s current needs an updated condition assessment and revision of the preservation scope is recommended.