• Improving Replacement Cost Data for NCDOT Highway Bridges

    NCDOT Research Project Number: 2017-09

Executive Summary

  • One of the primary functions of a bridge management system (BMS) is to inform data-driven, risk-based decision making by forecasting future network level needs and anticipating the costs and benefits of bridge replacement, rehabilitation, and preservation actions.  Of these actions, bridge replacement projects account for the majority of the current funding needs and annual allocations.  Consequently, shortcomings in conceptual cost estimating models used within bridge management systems can impose serious and potentially costly errors affecting financial needs projections and project selection and prioritization.  Conceptual cost estimating strategies currently used in the NCDOT BMS are simplified, do not consider factors affecting construction, preliminary engineering, and right of way costs, and have not been recently updated to reflect changes in construction cost trends and inflation.  In this study, cost data for recent bridge replacement projects completed in North Carolina were sourced and assembled into a database with information on the characteristics of the replaced and replacement structures.  This database was then used to evaluate current conceptual cost estimating strategies used by NCDOT, identify factors influencing construction, preliminary engineering, and right of way costs, and formulate new conceptual cost estimation models for bridge replacements.  Generalized linear regression models and decision trees were developed to estimate unit costs for each component of the replacement cost and cross-validation was used to arrive at appropriately sized models.  The developed cost estimation models were evaluated by comparing goodness of fit to the underlying project data as well as assessing the projected unit replacement costs obtained when applying the developed models to all bridges in the state.  The recommended conceptual cost estimation strategy uses generalized linear models to forecast unit construction and unit preliminary engineering costs and a decision tree to forecast unit right of way costs.  The recommended conceptual cost estimation strategy can be readily implemented within the existing BMS with few required changes and empirical evidence suggests that these revised models will significantly improve the accuracy of the conceptual replacement cost estimates.​
  
Matthew J. Whelan
Researchers
  
Matthew J. Whelan; Tara L. Cavalline
  
Brian Hanks
  
Mustan Kadibhai, PE, CPM

Report Period

  • August 1, 2016 – July 31, 2018

Status

  • Complete

Category

  • Structures, Construction and Geotechnical

Sub Category

  • Bridge Maintenance and Management

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