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From page 75... ... 75 In 2013 the White House defined resilience as "the ability to prepare for and adapt to changing conditions and withstand and recover rapidly from disruption," adding that "resilience includes the ability to withstand and recover from deliberate attacks, accidents, or naturally occurring threats or incidents."1 The first formal definition of resilience was provided in 1973 and focused on the ability of a system to absorb unusual disturbances and remain functional.2 Over the years, many other definitions of resilience have been proposed in science and engineering.3,4 Likewise, the field of resilience research has diversified into several areas of study (see Box 4-1) Read the entire page →
From page 76... ... 76 INVESTING IN TRANSPORTATION RESILIENCE BOX 4-1 Areas of Resilience Research Resilience research of the decline in functionality after disruptive events is divided into four different types of academic studies: system reliability, vulnerability, survivability, and recoverability. Reliability -- Research on reliability is useful in transportation resilience as a way to understand the occurrence of a hazard or disruptive event and the time interval between disruptions. Read the entire page →
From page 77... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 77 a Elsayed, E.A. Read the entire page →
From page 78... ... 78 INVESTING IN TRANSPORTATION RESILIENCE curve," which describes the evolution of functionality (or performance or level of service) over time after a disruptive event.5 The approach to resilience presented in this chapter builds on research into safety, reliability, and risk. Read the entire page →
From page 79... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 79 FIGURE 4-1 Relationship among safety and reliability, risk, and resilience.6 FUNCTIONALITY RECOVERY CURVES The resilience of a transportation system is related to its functionality during and after a harmful event. A common way to illustrate a system's resilience is to represent its functionality (or performance or level of service) Read the entire page →
From page 80... ... 80 INVESTING IN TRANSPORTATION RESILIENCE FIGURE 4-2 General functionality recovery curve. Figure 4-2 presents an example of a functionality recovery curve, where time (t) Read the entire page →
From page 81... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 81 instantaneous, like earthquakes, te and td occur nearly simultaneously. For events such as hurricanes or wildfires, however, the loss of functionality may occur more gradually over an interval of time. Read the entire page →
From page 82... ... 82 INVESTING IN TRANSPORTATION RESILIENCE FIGURE 4-3 Resilience curve illustrating non-uniform, pre-event system performance due to component deterioration and maintenance actions and nonlinear recovery phase. they tend to be continuous curves,16 which can be modeled analytically17 or through experimental observations and post-event measurements. Read the entire page →
From page 83... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 83 specific for each system, the associated resilience metrics can be defined in a general way and are said to be "event agnostic" and "system (or mode) agnostic." It is important to stress again that functionality metrics need to be specific to the area being studied, the mode of transportation, and in some cases even the hazard scenario. Read the entire page →
From page 84... ... 84 INVESTING IN TRANSPORTATION RESILIENCE FIGURE 4-4 Representation of resilience index as the normalized area under the functionality recovery curve. FIGURE 4-5 Illustration of the concept of "resilience triangle." th Sy st em F un ct io na lit y, F( t) Read the entire page →
From page 85... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 85 FIGURE 4-6 Example of a functionality recovery curve that includes the resilience metrics "minimum level of functionality" (Fmin) , "level of functionality restored at the end of the recovery process" (Ff) Read the entire page →
From page 86... ... 86 INVESTING IN TRANSPORTATION RESILIENCE Time to Reach a Target Level of Functionality Metrics for "time to reach a target level of functionality" report the time to reach a level of functionality that is less than 100% but still an important threshold. In Figure 4-6, the target functionality, Ftarget, is 75%, and t75 corresponds to the point in time when recovery activities have restored functionality to 75%. Read the entire page →
From page 87... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 87 TABLE 4-1 SPUR Model of Measuring Recovery from Earthquakes25 made up of the inherent coping capacity of the asset (or system) and baseline recovery response activities. Read the entire page →
From page 88... ... 88 INVESTING IN TRANSPORTATION RESILIENCE FIGURE 4-7 Illustration of the contribution to resilience from different actions: retrofitting, adding redundancy, providing effective recovery response, and increasing the resources available for recovery activities.26 vulnerability of components or assets, and increasing the resources available for recovery response activities. MODELS INCORPORATING UNCERTAINTY The metrics discussed in the previous section are deterministic -- they do not account for randomness. Read the entire page →
From page 89... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 89 Probabilistic hazard analysis is the science that studies the exposure of a region to hazards and assesses the probability of hazard events occurring and of reaching a certain level of intensity at each site.27,28,29 For transportation systems, it is important to know both the probability of exceeding a certain intensity level at each site and the probability of having a certain intensity occur simultaneously at various locations of the system. For this reason, the science of scenario selection was developed to pick specific extreme event scenarios in a way that is representative of all of the possible scenarios that a hazard source can generate.30,31,32,33 For a given scenario, the damage and recovery process also includes large amounts of uncertainty. Read the entire page →
From page 90... ... 90 INVESTING IN TRANSPORTATION RESILIENCE curves relate the intensity measure of an event at one location (e.g., the peak ground acceleration of an earthquake or the water depth in a storm surge) with the expected level of damage for a component or system. Read the entire page →
From page 91... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 91 FIGURE 4-8 Examples of probabilistic resilience metrics based on the functionality recovery curve. The gray curves in (b) Read the entire page →
From page 92... ... 92 INVESTING IN TRANSPORTATION RESILIENCE deviation, and quartiles of the resilience index. The same applies to the time to complete recovery, the time to reach a target level of functionality, the minimum functionality, and the other deterministic resilience measures. Read the entire page →
From page 93... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 93 BOX 4-3 Multi-Hazard Approach A multi-hazard analysis approach is essential if the best action to improve resilience to one hazard type may make the system less resilient to other possible hazards.a Consider, for example, a resilience enhancing action of locating power switches for generators in a secure, low-lying location. Given this decision, the facility might be more resilient to a human-made attack but could be more likely to fail under a flooding event. Read the entire page →
From page 94... ... 94 INVESTING IN TRANSPORTATION RESILIENCE humidity, salinity of the air) as well as the magnitude of their fluctuations. Read the entire page →
From page 95... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 95 ience should be related to the performance and services most relevant to the mission of the transportation agency. Moreover, functionality might be computed based on stakeholder perspectives and from either the engineering or user level.44,45 Typically, these functionality metrics relate to business continuity. Read the entire page →
From page 96... ... 96 INVESTING IN TRANSPORTATION RESILIENCE Weighted Sum of Assets in Service The functionality metric "weighted sum of assets in service" is especially useful for networks where not all links are equally important. For example, for the resilience tables mentioned in the previous section, if the target is set to "90% of roads open," it is necessary to specify what "90%" means. Read the entire page →
From page 97... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 97 the percentage of connected node pairs. More elaborate approaches weight each origin–destination pair by the corresponding volume of trips.60 Average added distance between locations above the pre-disruption value can also serve as a measure of connectivity.61 Metrics for Interdependent Systems or Facilities In infrastructure, the functionality of one system often affects the functionality of other systems. Read the entire page →
From page 98... ... 98 INVESTING IN TRANSPORTATION RESILIENCE tornadoes, flooding, and fire, methods for assessing post-event building functionality are still in the research stage.65 METHODS AND TOOLS FOR ANALYZING HAZARD MITIGATION To improve resilience, transportation agencies need methods to analyze investments designed to prevent damage and disruption and speed recovery. Off-the-shelf and ad hoc software tools developed for a specific purpose can assist investment analysis. Read the entire page →
From page 99... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 99 Mitigation Analysis Tools The Interdependent Networked Community Resilience Modeling Environment (IN-CORE) 67 and the Probabilistic Resilience Assessment of Interdependent Systems (PRAISys) Read the entire page →
From page 100... ... 100 INVESTING IN TRANSPORTATION RESILIENCE the framework presented in Chapter 5. Table 4-2 summarizes functionality metrics for a variety of modes and services. Read the entire page →
From page 101... ... CONTEMPORARY RESEARCH ON RESILIENCE AND RESILIENCE METRICS 101 Walking/Bicycling/Rolling Special-purpose lanes/trails Open/closed Sidewalks Accessibility Parking/shared mobility infrastructure Accessibility Air Transportation System level Connectivity, number of transfers, take-offs/ landings, throughput, number of travelers served Terminal/control tower/taxiway/ apron/ramps/aircraft stands/facilities (maintenance) /freight/parking/hangars Up/down, downtime Runways Open/closed, downtime, number of take-offs/ landings, on-time performance Fuel systems Availability IT/lighting/communications systems Up/down Waterways System level Connectivity, speed Docks/ports Open/closed Links Speed Locks Throughout capacity, open, closed Pipelines System level Flow rate Storage facilities Capacity, open, closed Surface-Aviation-Water Intermodal Terminals Facility Berth/to gate on arrival, open/closed, throughput, service times Power/IT/communication systems/ maintenance facilities Up/down, downtime Operators Throughput, service time, berth on arrival However, to use the concept of recovery curves for making investment decisions (i.e., in an a priori context) Read the entire page →
From page 102... ... 102 INVESTING IN TRANSPORTATION RESILIENCE resources deployed after a future disruption. Recovery curves also presume a perturbing or hazard event and thus require additional work to adapt them to the gradual, chronic, and likely permanent changes associated with climate change. Read the entire page →

From page 75...

... 75 In 2013 the White House defined resilience as "the ability to prepare for and adapt to changing conditions and withstand and recover rapidly from disruption," adding that "resilience includes the ability to withstand and recover from deliberate attacks, accidents, or naturally occurring threats or incidents."1 The first formal definition of resilience was provided in 1973 and focused on the ability of a system to absorb unusual disturbances and remain functional.2 Over the years, many other definitions of resilience have been proposed in science and engineering.3,4 Likewise, the field of resilience research has diversified into several areas of study (see Box 4-1)