Transit Safety Risk Assessment Methodologies (2021)

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70 Summary Table of SRA Methodologies A P P E N D I X C Method Industry Qualitative or Quantitative Summary MIL-STD-882 Defense, rail Qualitative The MIL-STD-882 is a risk assessment method that creates a matrix of probability and severity. Use quantitative data to assess probability when available. When quantitative data are not available for a given hazard or event, probability is assessed on judgment calls. Canadian Rail Qualitative The risk assessment must describe the circumstances that triggered the assessment, identify and describe the risks, identify the factors accounted for in the assessment, indicate for each risk the likelihood and the severity of the consequences, identify risks that require remedial action, and identify those remedial actions. European Common Safety Method Rail Qualitative The CSM is a policy triggered by an operational change that has the potential to impact safety. Risk is evaluated using historical data, a comparison to similar systems, and/or an application of codes of practice. The CSM is intended to ensure compatibility between European countries' systems, though each country will also be subject to that country's specific regulations as well. Bowtie Hazardous materials, energy Qualitative The bowtie is a risk assessment method that can be used to analyze and communicate how high- risk scenarios develop. The essence of the bowtie consists of plausible risk scenarios around a certain hazard, and ways in which the organization stops those scenarios from happening. The method takes its name from the shape of the diagram that you create, which looks like a man's bowtie. Event Tree Energy, aerospace, chemical Qualitative The ETA models the sequence of events that result from a single hazard or initiating event and describes how serious consequences can occur. The ETA can also be used for developing countermeasures to reduce the consequences. Fault Tree Aircraft, energy, rail, aerospace Qualitative Starting at an event that would be the immediate cause of a hazard or serious consequence (the top event), the analysis is carried out along a tree path. The combinations of causes are described with logical operators. Intermediate causes are analyzed in the same way, and so on back to basic events where the analysis stops. The method is graphical, and a set of standardized symbols is used to draw the fault tree.

Summary Table of SRA Methodologies 71   Method Industry Qualitative or Quantitative Summary process, manufacturing defect, a common human operator error, or some common external event. FMEA Aircraft, defense, rail Qualitative The purpose of FMEA is to identify and evaluate failure modes and probability, as well as to demonstrate compliance with safety requirements. The FMECA is more commonly used to analyze and control hazards. FMECA examines only hardware and software failures. Fault Hazard Chemical Qualitative Deductive method of (typically) qualitative analysis. The FHA requires a detailed investigation of subsystems. LOPA Chemical, rail Qualitative The LOPA is a tool that utilizes categories based on the orders of magnitude for frequency, severity, and likelihood of failure. The LOPA is often based on information from qualitative hazard analysis and implemented using a set of rules. The LOPA offers a risk analyst the ability to consistently evaluate the risk of a potential event. It can be applied when a scenario is too complex to make reasonable risk judgments based purely on qualitative judgment or as a screening tool. Fuzzy Reasoning Engineering, artificial intelligence, finance Quantitative This method estimates and evaluates risk based on failure frequency, consequence severity, and consequence probability. This method allows for better inclusion of approximate and difficult-to- quantify information. Slovakian Rail Rail Quantitative The Slovakian rail method uses the fault tree analysis and ETA for an accident progress scenario. When quantified historical data are not available, human error probability assessments, safety expert judgment, and statistical modeling (such as a Monte Carlo simulation) are used. Quantitative Risk Energy Quantitative The QRAs are built on actuarial events with logic models to predict frequencies and the causes of events. Probabilistic Risk Energy Quantitative The PRA data inputs include actuarial events with logic models to predict frequencies and the consequences of events. Rail Corridor Risk Rail, hazardous materials Quantitative This method uses a scoring method based on safety and security metrics. Additional factors can inform the decisions but do not directly impact the scores. Safety metrics are additive and security metrics are based on a peak number. The tool weighs security- and safety- related factors equally. The score is probability multiplied by consequences and is a weighted average. High-consequence targets are based on the presence of populations. Common Cause Defense, aircraft Qualitative This method identifies any accident sequences in which two or more events could occur as the result of one common event. These common causes or events may result from a common

Abbreviations and acronyms used without denitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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