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57 APPENDIX A Literature Review A literature review was conducted to investigate recent Risk-Based Bridge Management (3). This paper describes research and current state-of-practice related to performance a methodology for bridge project selection based on reliability measurement, risk assessment and risk management imple- methods and optimization procedures. The authors use a Mar- mentation by transportation agencies. The sources for the lit- kovian model to simulate deterioration of structural compo- erature review included FHWA reports, NCHRP reports, nents, and determine a reliability index for each element using published papers in professional journals (ASCE, TRR, etc.), either subjective assessment or first-order reliability methods. and current practices from Federal, state, and local agencies. The overall reliability of the bridge is calculated as system reli- This appendix summarizes the review, organized by risk man- ability by combining the individual reliability of the compo- agement, asset data and analytical tools, and performance nents in a series system. Risk is estimated with the reliability of management. the bridge and the consequence of closure. The paper discusses methods for finding the optimum set of repairs that minimize A.1 Risk Management the total network risk and describes use of a near-optimum algorithm for this application. The review of risk management literature focused on two primary areas: asset/operations-specific approaches to risk in Risk-Based Prioritization of Terrorist Threat Mitigation management systems; and statewide or regional approaches to Measures on Bridges (4). This paper discusses developing a management of catastrophic/severe risk. Two resources merit risk-based methodology to facilitate prioritization of terrorist special mention: the 2002 AASHTO Guide to Highway Vulner- threat mitigation strategies on individual bridges. This method- ability Assessment (1), and the draft final report for NCHRP ology was designed to focus on a single bridge and the risk of Project 20-59, Guide to Risk Management of Multimodal Trans- terrorist attack associated with each of its many individual portation Infrastructure (2), provided to the research team by structural components. The methodology evaluated the bridge NCHRP. Key concepts from theses resources are discussed in risk based on such factors as the component's importance to Chapter 3, and the two documents are summarized under a overall structural stability, its location and accessibility to ter- separate heading since they embody state and Federal agency rorists, and its resistance to the specific threat. The result of the level guidance documents that are different from the other methodology was a rank-ordered list of components most at research studies included in the review. risk to attack, allowing prioritization and optimization of the mitigation design for the bridge. Once mitigation schemes are Approaches to Risk in identified, the methodology can be utilized to recalculate miti- Management Systems gated risk, allowing for a direct indication of benefit/cost of the mitigation design. Many research studies have been conducted on the analysis and management of specific highway assets (especially bridges, A Risk-Based Decision-Support System for Bridge Man- tunnels, and roads) with risk-based methodologies. The risk agement (5). This paper presents a novel framework for a categories analyzed in these studies include terrorism, earth- risk-based decision-support system for an advanced bridge quake, and loss of structural or functional performance of management system. The authors suggest evaluating bridge assets. Several risk-based methodologies were developed for risk using structural safety reliability and anticipated conse- bridge management systems and highway maintenance man- quences of the bridge's failure. The system they describe agement systems using these concepts. includes components addressing inspection, data collection
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58 and storage, deterioration modeling, structural assessment, well as development of a general vulnerability rating based on economic appraisal of maintenance, MR&R actions through work originally performed by New York State Department of whole-life costing, work programming optimization method- Transportation. ologies, and a number of reporting facilities. Assessing and Managing Risk of Terrorism to Virginia's Risk-Based Asset Management Methodology for Highway Interdependent Transportation Systems (9). This study Infrastructure Systems (6). This study applies risk-based was conducted to assess and manage the risk of terrorism to models to highway maintenance management systems. The Virginia's interdependent transportation infrastructure. The authors developed a systemic risk-based asset management focus was to understand how the failure of one piece of infra- methodology as a decision-making tool for highway planners structure or any of its elements propagates in order to imple- and maintenance engineers to manage the maintenance of ment management policies that can mitigate the consequences. highway infrastructure systems. It uses several risk assessment and management models: the Hierarchical Holographic Model (HHM) for identifying risks; A Risk-Based Maintenance Management Model for Toll the Risk Filtering, Ranking, and Management (RFRM) for Road/Tunnel Operations (7). The focus of this study was ranking risks; the Inoperability Input-Output Model (IIM) for to develop a risk-based maintenance management model to accounting for direct and indirect impacts/consequences; and prioritize preventive maintenance activities for equipment in the Partitioned Multi-Objective Risk Method (PMRM) for complex plant installations like toll road/tunnel systems. The accounting for extreme events. At the statewide level, the direct resulting model is based on the five core elements of the risk and indirect economic impacts of transportation infrastruc- management process: identification, measurement, assess- ture disruptions (natural hazard, intentional attack, etc.) on ment, valuation, and control and monitoring. The model various dependent industry sectors are assessed using the IIM. requires participation of different departments to determine The industry impacts are measured in two metrics, economic the failure modes and effects of equipment and the corre- losses and percentage of inoperability. Workforce impacts are sponding preventive actions. The model can help operators also considered in the IIM in terms of income reduction and the to establish and determine suitable maintenance strategies for number of workers affected. The data from the Bureau of selecting the best courses of action in managing identified Economic Analysis (BEA) Input-Output Table and the risks. Regional I-O Multiplier System II (RIMS II) is used in IIM for ranking industry sector impacts. Census workforce data and Risk-Based Life-Cycle Costing of Infrastructure Reha- commodity flow data are used to quantify the disruption to the bilitation and Construction Alternatives (8). This paper transportation system produced by an act of terrorism. presents a new approach for estimating life-cycle costs and evaluating infrastructure rehabilitation and construction alter- Modeling the Impact of Infrastructure Interdependencies natives, derived from probability theory and simulation appli- on Virginia's Highway Transportation System (10). In this cation. In this study, highway pavement data are used to study, risk assessment and risk management techniques are demonstrate the model concept and development. The devel- used to identify system vulnerabilities and the risks associated oped risk-based life-cycle cost model considers the time to fail- with those vulnerabilities. HHM described above is used to ure of each pavement rehabilitation/construction alternative identify risks and vulnerabilities. Information used in HHM and provides additional knowledge about the uncertainty lev- includes jurisdictional, intermodal, economic and user per- els that accompany the estimated life-cycle costs. The paper spectives. A case study is presented focusing on risk manage- describes the various components of the developed model, the ment and finding ways to unlock the interdependencies of the factors affecting pavement performance and service life, the highway system to reduce the risks associated with those inter- statistical stratification process of highway pavement networks, dependencies. As part of the project findings, a sampling of risk and the data input modeling and simulation utilized for the management options is introduced in two categories: Response analysis. The model can help engineers in the decision-making (form response teams, alternative routes, redundancy in the process regarding the selection of pavement construction and system, etc.); and Unlock Interdependencies (alternate forms rehabilitation alternatives. of transportation, overstocking critical facilities, staggering work schedules, etc.). Approaches to Management Seismic Risk Assessment of Transportation Network of Catastrophic/Severe Risk Systems (11). In this study, the risk from earthquakes to a Several risk-based research studies have been conducted at transportation system is evaluated in terms of direct loss from the statewide or regional levels for highway infrastructure sys- damage to bridges and travel delays in the transportation net- tems on catastrophic/severe risk. They include terrorism risk work. The direct loss is estimated from repair costs due to dam- studies in Virginia and seismic risk studies in California, as age to bridges and is dependent on the size of the bridge and