Essential parameters for an Iowa bridge management system

Abstract

The objectives of this research were: 1) to document the current status of Bridge Management Systems (BMSs) and 2) to develop BMS-specific elements for the Iowa Department of Transportation (DOT). The results of the research will aid in the development of a BMS for the Iowa DOT by complementing a research project presently being performed for the California DOT (CALTRANS). The CALTRANS project is cosponsored by the Federal Highway Administration (FHWA) and CALTRANS. Its objective is to develop a generic BMS for use by other state DOTs. BMS elements investigated for the Iowa DOT included level-of-service (LOS) goals, agency costs, user costs, and bridge component deterioration rates. LOS goals are target values for characteristics used to assess bridge adequacy. Minimum acceptable and desirable LOS goals were established for load capacity, vertical clearance, clear deck width, and lateral clearance under the bridge. Agency costs are associated with bridge maintenance, repair, rehabilitation, and replacement. Iowa DOT agency costs were estimated by using historical data and questionnaires that were sent to the Iowa DOT district county engineers. The agency costs were incorporated into a computer program. This information is used to estimate costs for bridge repair alternatives or for a specific maintenance activity. User costs are incurred by the roadway user because of various LOS characteristic deficiencies. The user costs investigated for the State of Iowa included vehicle operating costs and accident costs. Accident rates and average daily traffic growth rates were also documented. Deterioration curves for bridge deck, superstructure, and substructure were developed for six categories of Iowa bridges. A Markov chain probabilistic approach was the basis for these curves. Iowa inspection data were used to formulate transition matrices that are the essential elements in the Markov chain model. When existing data were insufficient, an approximate approach based on linear regression was used. An interactive computer program was developed to produce the deterioration curves, which estimates the mean and the distribution of the future condition of a bridge component.