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Our Security Strategy

Systems-Based Perspective

In his speech outlining the results of the 2nd stage review for DHS, Secretary Chertoff stated that one of the DHS's core principles is that "our work must be guided by the understanding that effective security is built upon a network of systems that span all levels of government and the private sector."

A classic lesson in security is that a chain is only as strong as its weakest link.  This is particularly appropriate to transportation security.  A transportation system can be viewed as a set of interdependent links and nodes in which no element is secure if it can be influenced by a weak link. Because transportation security is interdependent in nature (research paper by Howard Kunreuther of the University of Pennsylvania and Geoffrey Heal of Columbia University - PDF 235 KB), our strategy must be built on a systems perspective.  Thus the transportation system can be thought of as a Complex Adaptive System (Hidden Order: How Adaptation Builds Complexity by John H. Holland), a system of interacting elements which adapt to each other over time.  The concept of a Complex Adaptive System (CAS) was drawn from a body of thought known as "complexity theory," (research paper by C.S. Holling - PDF 485 KB)  which offers at least two additional insights. 

• The system usually behaves non-linearly-which means that small perturbations in the system can sometimes lead to large outcomes
• The system displays "emergent properties"— which means that complex patterns can be based on seemingly random interactions among all elements of the system. 

These insights are key to understanding why TSA’s mission is to enhance transportation security while maintaining the free flow of commerce.  Terrorists seek to inflict damage that is out of proportion to their efforts by attacking parts of the system that will lead to non-linear consequences.  TSA must guard against that risk.  In seeking to minimize the impact of security measures, TSA seeks to ensure that the emergent patterns of commerce in our economy are not disrupted. 

One way to analyze a CAS is by characterizing it as a network.  In so doing, analysts can apply the tools of network theory (research paper by Mathew O. Jackson of the California Institute of Technology - PDF 1.1 MB) to understand the risks to the network.  Transportation networks consist of nodes and links.  For example, metro stations might be thought of as nodes while the tracks that connect the stations can be thought as links.  Likewise, Airports can be thought of as hubs and the routes they travel can be thought of as the links.  Different types of transportation will display different types of network topologies but networks can be classified in two basic categories:  Scale-Free and Random networks (research paper by R. Albert, H. Jeong and A. Barabasi of the University of Notre Dame - PDF 207 KB).

“Scale-free” networks have nodes which possess a significantly higher concentration of connections than the average node.  This type of network often resembles a hub and spoke system and they are very robust when faced with naturally occurring errors because the odds of a disruption hitting a key node are very low.  However, these networks are very vulnerable to attack because if a key node is targeted, the disruption will affect the whole system.

At the other end of the spectrum are “random” networks.  Random networks have a higher concentration of nodes with an average amount of connections.  Extreme amounts of connections are rare.  This network looks much more evenly distributed.   These networks are very robust when faced with attacks because there are very few “key nodes” to disrupt.  Yet these networks are more vulnerable to error because all nodes are approximately equally important.  Thus errors tend to diminish the performance more rapidly than in a “scale-free” network.

Network theory can also be applied to understand the terrorists themselves.  Many modern terrorist groups organize themselves into networks rather than hierarchies because networks tend to be more agile and resilient in response to their environments.  Networks are also more efficient in sharing information.  Because bureaucracies tend to handle ambiguity poorly, net-centric adversaries pose a particular problem for hierarchical bureaucracies.  Net-centric terrorist organizations try to exploit gaps between traditional bureaucracies. 

TSA recognizes that it takes a network to fight a network (research paper by John Arquilla - PDF 120 KB).  TSA is working to strengthen our network of federal and industry partners.  Utilizing this network, we will identify the areas of greatest risk throughout transportation systems and act to prevent attacks and mitigate their potential consequences.

As secretary Chertoff has stated, “For our department, risk management starts with weighing threats, vulnerabilities and consequences of a potential terrorist attack or catastrophic event, then conducting a rigorous, information-driven analysis both to set priorities for resources and to give focus and strategic direction to our policies and programs.”  By applying the concepts of complexity and network theory to transportation security, TSA can more effectively identify threats, vulnerabilities, and consequences that characterize the risk to our transportation system.   Complexity and network theory also help TSA target resources to be allocated to the highest risks in the transportation system while minimizing the impact to the free flow of commerce.  Finally, these concepts have helped TSA and other organizations to structure themselves and their partnerships to more effectively fight terrorism.