Modeling of Life-Cycle Alternatives in the National Bridge Investment Analysis System

The FHWA has developed the National Bridge Investment Analysis System (NBIAS) as a tool to analyze bridge investment needs and predict future bridge conditions and performance at a national level. NBIAS analyzes each bridge in the national inventory for each year in a multiyear analysis period through a program simulation model. In the model the system simulates deterioration, traffic, preservation needs, functional needs, and costs. The modeling approach used in prior versions of the system was initially based on that implemented in the Pontis Bridge Management System. Though the modeling approach has evolved over time, its fundamentals are well-established and have been discussed previously in the literature. Recently FHWA developed Version 5.0 of NBIAS introducing fundamental changes in the NBIAS modeling approach. This paper details the revised modeling approach implemented in NBIAS 5.0, focusing on the modeling of multiple life-cycle alternatives for each bridge. In previous versions of NBIAS, the system prioritized bridge alternatives (allowing for the possibility there may be multiple alternatives on a bridge) using the Incremental Benefit–Cost Ratio (IBCR) heuristic. This approach involves calculating the IBCR of each alternative relative to the next cheaper alternative, and prioritizing alternatives in order of decreasing IBCR. Funds are then allocated to the list of alternatives until they are expended. This approach is repeated for each year of the analysis period, which may be up to 50 years. The IBCR heuristic has been shown to yield a near-optimal solution for prioritizing capital projects given certain conditions. However, it is not designed to support multiple budget constraints. Also, because the system simulates in a year-by-year manner, it may produce a suboptimal result in some cases when results are viewed over multiple years, particularly if additional constraints are added to the system. The basic approach implemented for NBIAS 5.0 was to shift from a simulation model that generates and prioritizes bridge alternatives year-by-year to one that generates and prioritizes multi-year alternatives. In this version the system first generates a set of 21 different life cycle alternatives for each bridge, reflecting different strategies concerning timing of preservation and functional improvement work. The system then uses a modified IBCR heuristic termed “MINCBEN” previously developed for the Virginia Department of Transportation to select life-cycle alternatives given a matrix of budget constraints specified by work type and year. This revised modeling approach provides improved modeling of trade-offs between bridge preservation and replacement, better optimizes resource allocation over time, and allows for flexibility in setting budget constraints by work type and year.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; References; Tables;
  • Pagination: pp 100-113
  • Monograph Title: Eleventh International Bridge and Structures Management Conference
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 01672045
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Jun 14 2018 9:17AM