Preserving Historic Bridges: Strategies to Overcome Obsolescence

Abstract

The National Historic Preservation Act of 1966, and Section 4(f) of the U. S. Department of Transportation Act of 1966 require federal agencies to have a long term preservation plan in place for historic bridges under their jurisdiction. As agents of federally funded bridge programs, state transportation agencies are tasked with implementation of a statewide preservation plan. The Texas Department of Transportation (TxDOT) is responsible for monitoring the condition of the 49,829 publicly owned bridges. Of these 32,647 are administered directly by TxDOT as part of the State Highway System (on system bridges), and 17,155 are under the jurisdiction of local entities (off system bridges). Approximately 127 on system bridges and 257 off system bridges, a total of 384 bridges, are designated historic. Because they must serve the ever increasing demands of the transportation infrastructure, most of these historic bridges are at risk of being abandoned or destroyed in the wake of federally funded efforts to eliminate structurally deficient and functionally obsolete bridges from the transportation system. In the mid 1990s TxDOT intensified the effort to implement a comprehensive and proactive program to preserve historic bridges endangered by TxDOT projects. In several initiatives, interdisciplinary teams of rank and file employees were utilized to define objectives, and develop procedures for meeting those objectives based on consensus. Different preservation strategies evolved for three basic outcomes of historic bridge rehabilitation: 1) full vehicular service; 2) reduced level of vehicular service; and, 3) adaptive (non vehicular) use. Because of these strategies, TxDOT has been able during the past decade to restore and extend the life of many of the best examples of historic bridges in the State. This paper will describe some of these successful projects to illustrate the implementation of preservation strategies.