National Academies Press: OpenBook

Freight Transportation Resilience in Response to Supply Chain Disruptions (2019)

Chapter: Framework for Making Supply Chains More Resilient

« Previous: Characteristics of Disruptions
Page 133
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 133
Page 134
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 134
Page 135
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 135
Page 136
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 136
Page 137
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 137
Page 138
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 138
Page 139
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 139
Page 140
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 140
Page 141
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 141
Page 142
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 142
Page 143
Suggested Citation:"Framework for Making Supply Chains More Resilient." National Academies of Sciences, Engineering, and Medicine. 2019. Freight Transportation Resilience in Response to Supply Chain Disruptions. Washington, DC: The National Academies Press. doi: 10.17226/25463.
×
Page 143

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

133 Note: Military deployments in this context represent disruptions to normal operations of transportation facilities, such as seaports. Figure 6: Disruption Classification The concept in Figure 6 is presented as a descriptive framework for the types of events that characterize system disruptions. However, the framework also provides an important perspective on the level of risk an agency or firm is willing to adopt with respect to supply chain disruptions if the likelihood of an event occurring is superimposed over the two dimensions shown. For example, without considering the likelihood of an event, one would focus on the "severe" impact events in Figure 6. This calculation is altered when the likelihood of the event occurring is taken into consideration. Assume that the likelihood of a terrorist attack against one of your facilities that would be severely damaging is quite low. Compare this event to one that might occur more often but when it does the disruption is small (e.g., snow storm). Decision makers would have to decide how to allocate funds to prepare and respond to these types of events, with specific attention given to the perceived risk and duration of disruption if the more disruptive event does occur. FRAMEWORK FOR MAKING SUPPLY CHAINS MORE RESILIENT The process of making supply chains more resilient is based on a series of steps that investigate where vulnerabilities and risks of disruptions exist in the supply chain. This leads to specific strategies for making the supply chain more resilient. The process of thinking through enhancing a particular system's resilience has been examined from a variety of perspectives in many different disciplines, notably with the logistics literature. The concept of a resilient transportation system and the role of transportation agencies in its operation have received increasing attention from many of the participants in supply chains and the transportation systems that support them. Some of the earliest research occurred in the late 1970s in response to the Arab oil embargoes when declining supplies of petroleum imports caused many transportation officials and agencies to examine the resilience of the transportation system to this “shock.” Since the mid-2000s, the volume of research and reporting on resilience in its many aspects

134 within the transportation community has become voluminous and dispersed throughout the Transportation Research Board (TRB) modal and subject area domains.7 This guidance is based on the following process, which is an amalgam of the many different frameworks that were investigated by this research. In particular, the development of this process was influenced by a concurrent NCHRP project 20-117 that is examining how to incorporate resilience concepts into state transportation agencies. As part of that project a resilience framework was proposed for conducting an assessment of the strengths and weaknesses of an agency's resilience efforts. Parts of the framework developed in NCHRP20-117, amended based on the results of this present research project, serve as the basis for the following guidance, which is organized around the seven steps shown in Figure 7. These steps consist of the following typical activities. Step 1: Organize for Success – Identify responsibilities for improving supply chain resilience or the components of the transportation system for which your agency/firm is responsible. Establish organizational mechanisms and institutional relationships that will serve as the foundational partnerships as you move forward with the process. If necessary, institutionalize these partnerships with formal agreements, protocols or understandings (these most often emphasize who is responsible for what). Ensure that those responsible are supported by leadership and have sufficient resources to succeed. Step 2: Develop a Communications/Information Exchange Strategy – Think about the information channels that need to be established for this effort to be successful. Who are the key participants? What is the best way to reach out and engage them in the process? Develop or enhance current communication strategies both during the resilience planning process and during emergency response efforts. Understand what types of information will be necessary to support and maintain the resiliency planning process. Step 3: Assess Current Practice – Focus on what you and your partners are currently doing with respect to infrastructure provision and system operations. Are you designing key infrastructure with resilience in mind? Has your continuity of operations plan been updated recently? Does your staff have the knowledge, expertise and resources to promote resilience in supply chains? Step 4: Understand Hazards and Threats and Their Impacts/Consequences – This step is perhaps one of the most critical in that enhancing supply chain resilience depends on the type, expected duration, and nature of the expected disruptions. This assessment could be comprehensive by looking at all the types of threats and impacts that might be faced, or it could focus on the one or two threats expected to be most likely or most impactful. This step will also vary by the level of detail desired, the degree to which other background information is already available from other sources (e.g., future flooding locations from already-conducted adaptation studies), and the amount of resources (both funding and human expertise) available to conduct this assessment. 7 As of this writing, 215 security/emergency management/infrastructure protection-related planning and implementation projects have been initiated through programs managed by the Transportation Research Board (TRB). Guidance users are encouraged to see the updated Cooperative Research Programs, Security, Emergency Management, and Infrastructure Protection Research Status Report found on the NCHRP website.

135 Step 3: Assess Current Practice Step 1:Organize for Success Step 2: Develop a Communications Strategy/Plan Step 4: Understand the Hazards and Threats Enhance emergency response capabilities Prioritize detailed assessments Undertake detailed assessments Step 6: Implement Strategies and Actions Step 7: Monitor System Performance System Operations Capital Improvements Step 5: Develop Strategies/Actions Including “Early Wins” Figure 7: Resilient Supply Chain Assessment Process Step 5: Develop Strategies, Actions and Plans – Based on the assessment from Step 4, collaboratively identify strategies, actions and plans that can be put in place to improve supply chain resilience. These actions could focus on issues internal to your organization or on improving the relationships among key participants in the supply chain. The breadth of actions is quite broad, ranging from actual infrastructure changes, changes to standard operating procedures, enhancements to existing institutional relationships, training for staff and so forth. This step also includes identifying "early wins", which is designed to establish credibility in the process by identifying actions/strategies/ projects that can be implemented in the short term (and hopefully without much financial support). This could include physical changes to projects already in the development stage, changes in protocols, changes to emergency response/operational strategies, or training opportunities for staff. Step 6: Implement Strategies and Actions – This step includes identifying which of the strategies and actions from Step 5 should proceed to implementation based on organizational capabilities and resources, and which of these actions will have to be implemented at a later date. Implementation plans would include those actions that can be taken solely by one agency, and those that will require joint efforts, and if so, how the responsibilities will be divided among those involved. Step 7: Monitor Performance and Incorporate into Assessing Current Practice – Provide feedback into the planning process as well as to the responses to disruptions when they occur. Based on actual experience with disruptions, what should be done differently to enhance supply chain resilience in the future? How can operations be improved as well as how is infrastructure provided?

136 Several observations concerning this process merit special attention. 1. This process can be used by a single agency or organization, or it could be conducted jointly with many others. For example, in the context of making the supply chain more resilient, there are steps in the process that would greatly benefit from collaboration among the different participants in the supply chain. These include understanding what the hazards/threats and the likely impacts/consequences will be; developing strategies/actions/plans in response; implementing strategies and actions; monitoring the performance of responses to disruptions; and learning from this experience. 2. This process, however, does recognize that it will often be difficult to engage many of the supply chain participants throughout the process, in particular, firms and companies that provide the transportation, logistical and shipping services. Thus, part of the process of thinking through how to enhance supply chain resilience includes identifying the steps where such engagement is critical and will be perceived as meaningful by these participants; and then encouraging such involvement. 3. Part of Step 5 includes "Identify Early Wins," which is aimed at not only implementing actions that will improve the resilience of the supply chain, but also actions that are intended to establish credibility in the process (in other words, participating in the process actually results in progress, particularly important for private sector participation). 4. The process includes resilience strategies aimed at improving both the operations/emergency response capabilities of the involved parties, as well as improvements to physical infrastructure that would protect from, or minimize damage caused by, future disruptions. Step 8, monitoring performance and incorporating the results into assessing current practice, thus examines how agencies and firms responded to disruptions as well as how infrastructure strategies and designs actually resulted in improved resilience. 5. As noted throughout the guidance, the efforts to increase the resilience of the supply chain to hazards and threats will depend on the type of threat, and the expected magnitude and scope of the impacts. The process outlined in Figure 7 is not intended to provide guidance on every possible combination of hazards, threats, impacts, consequences and participants. However, it is intended to portray a way of thinking about the steps necessary to protect the supply chain and promote a more resilient freight transportation system performance. The following sections provide more detailed guidance on each step of this resilience assessment process. Depending on where your organization is with respect to examining the resilience of supply chains or of the transportation system that serve as the basis for commodity movement, some of the steps might have largely been accomplished, at least within the organization. Most major transportation carriers have some structure or protocol for responding to disruptions and for interacting with other groups in this response. Plans for business continuity and continuity of operations are found in many agencies and firms; others have a rudimentary understanding of what to do in case of major system disruption. The format for the guidance is a series of questions that form the basis for establishing a capability in each step. The questions can be organized into a scoring system if so desired to provide a sense of how many of the characteristics of good practice are present in the current process (similar to that done with capability maturity models). At the very least, the questions serve as a guide on what types of information and actions could lead to a more resilient supply chain.

137 STEP 1: ORGANIZE FOR SUCCESS Yes No Internal to your Organization Have you identified the roles and responsibilities for executive level championing of resilience throughout the organization? Have you established clear responsibilities for planning for a more resilient supply chain or for a more resilient transportation system (if a public agency)? Have you established clear responsibilities and formal protocols for responding to disruptions to the supply chain or for disruptions to components of the transportation system that would have a major impact on supply chains (if a public agency)? Have you developed formal, multi-participant (to your organization) plans to examine the implications of supply chain disruptions to your organization and its customers? Does your organization provide training for the staff responsible for the supply chain or for the transportation system used by supply chains on resilience-related topics? External to your Organization Have you identified your key partners in your own business/sector that would be important to make the supply chain more resilient (e.g., private firms would consider customers, logistics providers, other shippers, etc. and public agencies would consider other public owners of relevant infrastructure, enforcement agencies, regulatory agencies, etc.)? Have you identified key participants outside of your own business/sector that would be important to make the supply chain more resilient (e.g., private firms might consider public agencies and public agencies might consider freight carriers)? Have you undertaken collaborative efforts at planning for a more resilient supply chain or a more resilient transportation system (if a public agency)? Have you established formal agreements or protocols among key supply chain participants establishing their respective roles in planning for a more resilient supply chain? Have you established formal agreements or protocols among key supply chain participants that identify their respective roles in responding to supply chain/system disruptions? Yes No Total 8 - 10 Yes Your organization is well-organized to provide more resilient supply chains 5 - 7 Yes Your organization is well-positioned to be better prepared to enhance the resilience of supply chains; additional steps are necessary to enhance organizational capacity. 9 0- 4 Yes Your organization needs new or enhanced organizational capacity to improve supply chain resilience

138 STEP 2: DEVELOP A COMMUNICATIONS /INFORMATION EXCHANGE STRATEGY Yes No Internal to your Organization Have you developed a strategy for communicating information on the importance of resiliency to agency staff and to their job within the agency? Have you developed and periodically updated (based on lessons learned from prior incidents) a strategy for communicating internally during supply chain disruptions? Do you have a contingency plan in the event normal communications means or outlets are disrupted as well (e.g., cyberattack)? Do you periodically assess the feasibility of new information dissemination technologies in order to update the agency's communications strategy? Do you provide training for the staff responsible for communicating the specifics of a system disruption and how to deal with public and social media? External to your Organization Have you met with external stakeholders, system users, customers, etc. to discuss the most effective way of communicating information about supply chain disruptions? Have you developed a strategy for communicating the importance of resiliency to a range of key audiences and stakeholders? In anticipation of major system disruptions that will involve more than one group or organization, is a protocol in place that establishes lines of communication and responsibilities for disseminating information? Have you developed a strategy in collaboration with key stakeholders and partners for disseminating information to supply chain/transportation system users during system disruptions? Have information templates been prepared to disseminate information to the broader public during system disruptions? Yes No Total 8 - 10 Yes Your organization has established a good communications strategy relating to resilient supply chains; efforts should be made periodically to strengthen this strategy. 5 - 7 Yes Your organization is well-positioned to enhance the communications/ information exchange strategy as it relates to supply chain resilience; additional steps are necessary to enhance the communications capability. 0 - 4 Yes Your organization needs a better strategy for communications and information exchange.

139 STEP 3: ASSESS CURRENT PRACTICE Yes No Internal to your Organization Have you assessed how your agency is doing with respect to enhancing the resilience of supply chains/transportation systems? Have you conducted an internal hazards and threats role-playing exercise to assess your organization's readiness to respond to disruptions? Have you conducted an assessment of the training and professional development needs of the staff responsible for enhancing supply chain/transportation system resilience? Have you examined past supply chain/transportation system disruptions to identify where improvements to organizational capacity can be made? Have you examined the project planning protocols/design criteria for the physical infrastructure that is part of your responsibility in the supply chain for their sensitivity to system resilience? External to your Organization Have you engaged with external stakeholders to identify concerns/opportunities they have with respect to your organization's response to disruptions? Have you assessed the effectiveness of your agency’s for interacting with external stakeholders in order to enhance supply chain resilience (in a pro-active sense)? Have you assessed the effectiveness of your agency’s strategy for interacting with external stakeholders for responding to system disruptions (in a reactive sense)? Have you conducted a multiple-participant hazards and threats response role-playing exercise to assess the readiness to respond to disruptions? Have you looked at peer organizations to identify best practice in identifying how organizations assess their effectiveness in supply chain/system management efforts? Yes No Total 8 -10 Yes Your organization has done a good job at assessing its capacity to provide resilient supply chains; efforts should be made periodically to strengthen this capacity by conducting self-assessments. 5 - 7 Yes Your organization is well-positioned to enhance the self-assessment process by identifying targeted strategies for improving the assessment process; additional steps are necessary to enhance this assessment capability. 0 - 4 Yes Your organization needs a better strategy for critical self-assessments, with more attention given to key gaps identified above.

140 STEP 4: UNDERSTAND HAZARDS AND THREATS AND THEIR IMPACTS/CONSEQUENCES Yes No Internal to your Organization Have you identified potential hazards and threats that will result in disruptions to the supply chain/transportation system and the implications to your organization's response and recovery efforts? Have you made systematic and structured efforts to identify where in your network redundancy does NOT exist such that impacts to system users will likely be more significant? Have you identified the most critical facilities, assets, intermodal connections, movements and/or corridors under your organization's control that require greater attention with respect to system vulnerability? Have you studied the expected economic and financial costs associated with a transportation system disruption? Have you examined the impacts of different types of disruptions to your work force and identified strategies for supporting employees during times of stress? External to your Organization Have you participated in a group (multi-stakeholder) exercise to identify the types of potential disruptions to the supply chain and the resulting impacts? Have you identified the most critical facilities, assets, intermodal connections, and movements that are NOT under your organization's control but whose disruption would cause serious deterioration of system performance? Have you included different system users in a pre-disruption assessment to understand their needs during a disruption? Have you included an understanding of impacted communities and possible organizational responses in a pre-disruption assessment? Have you examined the cascading effects of disruptions to other infrastructures and services on the supply chain/transportation system (e.g., disruptions to the power grid or communications networks)? Yes No Total 8 - 10 Yes Your organization has done a good job at assessing the hazards and threats that could potentially affect the supply chain; efforts should be made periodically to strengthen this capacity by conducting self-assessments. 5 - 7 Yes Your organization is well-positioned to better understand the hazard and threats facing the supply chain and their implications; additional steps are necessary to enhance this understanding. 0 - 4 Yes Your organization needs to better understand the hazards and threats facing the supply chain/transportation system and how they affect your organization.

141 STEP 5: DEVELOP STRATEGIES, ACTIONS, AND PLANS Yes No Internal to your Organization Do you have a continuity of operations/business continuity plan that has been updated in the past three years? Have you developed operations and maintenance strategies that will lead to a more effective response to a future disruption? Have you developed emergency response strategies/actions that will lead to a more effective response to a future disruption? Have you identified changes to project planning protocols/design criteria for the physical infrastructure (that is part your responsibility in the supply chain) for their sensitivity to system resilience? Have you developed cyber/information system security strategies, action or plans that will protect the command and control systems of the supply chain? External to your Organization Have you engaged with external stakeholders to change the type or performance characteristics of the physical infrastructure that supports the supply chain? Have you engaged with external stakeholders to change service and/or operations/strategies/actions that will enhance supply chain/transportation system resilience? Have you engaged with external stakeholders to change emergency response strategies/actions that will enhance supply chain/transportation system resilience? For key potential bottleneck/choke points in the event of a disruption, have you preplanned alternate routes/detours and/or modes in coordination with relevant agencies? Have you looked at peer organizations to identify best practice for different types of supply chain/system resilience strategies and actions? Yes No Total 8 -10 Yes Your organization has done a good job in developing strategies and actions that will enhance supply chain/transportation system resilience; efforts should be made to maintain or enhance these efforts where appropriate. 5 - 7 Yes Your organization is well-positioned to develop more strategies and actions to enhance supply chain/transportation system resilience. Efforts should be made to develop additional strategies/actions. 0 - 4 Yes Your organization needs to identify strategies and actions to enhance supply chain resilience/transportation system resilience.

142 STEP 6: IMPLEMENT STRATEGIES AND ACTIONS Yes No Internal to your Organization Have you directed the responsible staff for implementing resilience strategies, actions or plans to examine where in the implementation process improvements can be made to improve strategy/action delivery? Have you implemented changes in operations and maintenance strategies/actions that will lead to a more effective response to a future disruption? Have you implemented emergency response strategies/actions that will lead to a more effective response to a future disruption? Have you implemented changes to project planning protocols/design criteria for the physical infrastructure (that is part your responsibility in the supply chain) for their sensitivity to system resilience? Have you developed contingency plans for key terminals/facilities consisting of specific strategies and actions that can be taken for different disruption scenarios? External to your Organization Have you implemented changes in operations and maintenance strategies/actions involving external organizations that will lead to a more effective response to a future disruption? Have you implemented emergency response strategies/actions involving external organizations that will lead to a more effective response to a future disruption? Have you implemented changes involving external organizations to project planning protocols/design criteria for physical infrastructure that will lead to enhanced system resilience? Have you worked directly with partners or other stakeholders to improve the collaboration in implementing resilience-oriented strategies/actions? Have you looked at peer organizations to identify best practice in how to implement resilience strategies and actions? Yes No Total 8 -10 Yes Your organization has done a good job in implementing resilience strategies/actions that will improve the resilience of the supply chain/transportation system; efforts should be made to maintain or enhance these efforts where appropriate. 5-7 Yes Your organization is well-positioned to improve its implementation capabilities with respect to supply chain/transportation system resilience strategies/actions. Additional efforts should be made to improve implementation capacity. 0-4 Yes Your organization needs a better strategy for implementing resilience strategies/actions, with more attention given to key gaps identified above.

143 STEP 7: MONITOR PERFORMANCE AND INCORPORATE INTO CURRENT PRACTICE Yes No Internal to your Organization Have you developed and used system measures to monitor the resilience of the supply/chain transportation system (so-called outcome measures)? Have you developed and used measures to monitor agency actions with respect to system resilience (so-called output measures)? Has measuring system resilience influenced agency decisions and/or operations? External to your Organization Do you monitor performance measures of other agencies or systems as part your own efforts (e.g., monitoring congestion levels on the road network provided by state transportation agencies)? Do you participate with other organizations to help in their efforts to develop system performance measures to ensure that supply chain resilience is considered in their system monitoring? Yes No Total 5 - 6 Yes Your organization has done a good job at incorporating performance-oriented planning and decision making into the operating structure; efforts should be made to maintain or enhance these efforts where appropriate. 3 -4 Yes Your organization is well-positioned to improve its efforts at monitoring the resilience of the supply chain/transportation system. Efforts should be made to develop additional strategies/actions for supply chain/transportation system resilience monitoring. 0 - 2 Yes Your organization needs a better strategy for monitoring the resilience of the supply chain/transportation system.

Next: Strategies for Enhancing Supply Chain/Transportation System Resilience »
Freight Transportation Resilience in Response to Supply Chain Disruptions Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Freight Research Program (NCFRP) has released a pre-publication version of Research Report 39: Freight Transportation Resilience in Response to Supply Chain Disruptions. The report provides guidance to public and private stakeholders on mitigating and adapting to logistical disruptions to supply chains resulting from regional, multi-regional, and national adverse events, both unanticipated and anticipated.

The report, which makes a significant contribution to the body of knowledge on freight transportation and system resiliency:

(1) assesses research, practices, and innovative approaches in the United States and other countries related to improving freight transportation resiliency;

(2) explores strategies to build relationships that result in effective communication, coordination, and cooperation among affected parties;

(3) identifies factors affecting resiliency;

(4) analyzes potential mitigation measures;

(5) characterizes spatial and temporal scale considerations such as emergency planning and response timeframes;

(6) prioritizes response activities by cargo types, recipients, and suppliers;

(7) identifies potential barriers and gaps such as political boundaries, authorities, ownership, modal competition and connectivity, and social and environmental constraints; and

(8) examines the dynamics of supply chain responses to system disruptions.

The report also includes a self-assessment tool that allows users to identify the current capability of their organization and institutional collaboration in preparing for and responding to supply chain disruptions.

Disruptions to the supply chain and their aftermath can have serious implications for both public agencies and companies. When significant cargo delays or diversions occur, the issues facing the public sector can be profound.

Agencies must gauge the potential impact of adverse events on their transportation system, economy, community, and the resources necessary for preventive and remedial actions, even though the emergency could be thousands of miles away.

Increasing temporary or short-term cargo-handling capacity may involve a combination of regulatory, informational, and physical infrastructure actions, as well as coordination across jurisdictional boundaries and between transportation providers and their customers.

For companies, concerns can include such issues as ensuring employee safety, supporting local community health, maintaining customer relationships when products and goods are delayed, and ultimately preserving the financial standing of the company.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!