Assessing Infrastructure Deficiencies: The Case of Highway Bridges

This paper assesses deficiencies in highway bridges as a case study of the present state of an important segment of the nation's infrastructure. The National Bridge Inventory (NBI) contains a considerable amount of information about the characteristics of the U.S. highway bridge population. Condition ratings reflect physical deterioration due to environmental effects and traffic, and appraisal ratings indicate changes in traffic volume, existing load capacities, and compliance with safety standards related to bridge geometry and clearances. Expressed in percentages of bridge counts, the major deficiencies defined by low ratings rank as follows: deck geometry; structural evaluation; and conditions of substructure, superstructure and deck. Rank and percentages of deficiencies vary by superstructure material. Generally, structural deficiencies are lower for concrete bridges than for steel or timber bridges. Funding and maintenance policy differences among states and local governments are evident from the percentages of newly constructed or reconstructed bridges rated deficient and from the changes in the various deficiencies with age. The rates of increase with bridge age of the major deficiencies raise an interesting question: Are transportation growth and increase in vehicular loads more important than maintenance as causes of highway bridge deficiency or obsolescence?