# A Novel Decision Support System for Long-Term Management of Bridge Networks
## 1 Introduction
### State of Practice in Bridge Management  
The bridge management practice in the United States has improved significantly over the last 40 years both at the federal and state levels. At the federal level, the National Bridge Inspection Standards (NBIS) unifies the method of data collection and condition assessment on public highway bridges [8]. The collected inspection data by the state DOTs are submitted to FHWA annually in a nationwide reporting/coding format that is later entered into the NBI database [9]. Based on NBI, bridge owners are able to monitor the condition and performance of their bridges to make accurate management decisions.  
Figure 1: SHM at local and global levels using noncontact methods and advanced decision making.  
FHWA imposes an appraisal rating on all government-owned bridges through routine inspections that are recorded to NBI. The appraisals of bridges are carried out by scoring the bridges in three categories: structural adequacy and safety, serviceability and functional obsolescence, and essentiality for public use. After the scores in these categories are summed, special reductions are made. The resultant score will give the sufficiency rating that could be used for ranking bridges for infrastructure management. The sufficiency rating in NBI's bridge appraisals basically receives input from local and global assessments as well as some additional parameters. At the state level, state DOTs may have different procedures regarding bridge asset management, funding, maintenance considerations, and resource allocation. A comprehensive National Cooperative Highway Research Program (NCHRP) synthesis report published by the Transportation Research Board (TRB) puts out the differences in state practices and explains the reasons of the variety in the bridge management practices mainly on the following issues: the differences in the policy, financial, technical and institutional operations as well as the different approaches to planning, programming and budgeting [10]. According to the interviews conducted within the synthesis study, mixed centralized and decentralized management strategies are followed in many agencies. In contrast to the bridge replacement and rehabilitation projects, which can be funded by the federal Highway Bridge Program (HDP) and thus are centralized, the maintenance and repair projects are decentralized by being funded internally. In order to maintain communication between centralized and decentralized decisions, many states employed a bridge management system (BMS), which incorporates detailed state procedures at the element level and NBIS requirements at the federal level [11]. Although BMS has limited use toward decision making, state agencies find it helpful in terms of compilation of data and display of short-term and long-term information [12]. According to the NCHRP study, the characteristic use of BMS for state DOT decision making is analyzed as follows:  
* Technical aspects in the decision making such as condition assessment and performance assessment are mainly held in BMS rather than economic and social analyses that involve life cycle cost analysis, social impact analysis, etc.;
* The decision making based on BMS output is generally for short-term rather than long-term purposes, and the recommended actions are not proactive of future predicted conditions by lacking predictive models and scenario analysis;
* The decision-making models usually do not recommend multiple action strategies with a comparative analysis.