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Recommendations for Bridge and Tunnel Security

Section 2 Blue Ribbon Panel Approach

2.1 Overall Strategy for Bridge and Tunnel Security - "The Bigger Picture"

Bridge and tunnel security, like security for any infrastructure asset, includes a broad range of issues that must be addressed to ensure that adequate measures are taken to protect the asset and the people and goods that utilize the asset. Table 1 shows the bridge and tunnel security issues considered by the panel organized into topical areas. Several of the topics and related issues are of general interest and apply to all transportation infrastructure; others relate more directly to bridges and tunnels. For example, the "management and operational practices" issues apply to most infrastructure assets (transportation and otherwise), as do "information security," "mobilization and response," and "recovery" issues. However, issues that fall within the "planning, design, and engineering" area may be unique to bridges and tunnels and require special solutions that go beyond what might be needed to reduce the vulnerability and improve the security of other infrastructure assets.

Table 1. Bridge and Tunnel Security Issues
Key Topics in Infrastructure Security Specific Issues
  1. Foundations for Policy
  • Criteria Establishing Investment Priorities
  • Institutional Continuity
  1. Planning, Design, and Engineering
  • Design Review for Secure Structures
  • Research and Development (R&D) Needed to Support "Design for Security"
  • Design Criteria
  • Design Specifications
  1. Management and Operational Practices
  • Best Practices
  • Practice Review
  • Institutional Relationships
  • Preparedness
  • Personnel and Vehicle Security
  • Communication/Outreach
  1. Information Security
  • Procurement Practices
  • Information Security
  1. Mobilization ("Notice") and Response ("Trans-event")
  • Threat Warning
  • Early Response
  • Initial Response
  1. Recovery (Post-event)
  • Damage Assessment
  • Functional Continuity

The panel's special expertise is in the area of bridge and tunnel planning, design, and engineering; therefore, the primary focus of recommendations contained in this report addresses near- and long-term design and engineering solutions to bridge and tunnel vulnerabilities.

2.2 Framework for Planning, Design, and Engineering

During its initial meeting, the BRP established a framework for addressing bridge and tunnel security. This framework includes the following elements considered essential to developing sound recommendations for reducing bridge and tunnel vulnerability to terrorist attacks:

  • A means of identifying "critical" bridges and tunnels, through prioritization and risk assessment
  • Designation of the specific threats to be considered "terrorist attacks" (e.g., to eliminate military attacks with precision guided munitions)
  • Determination of the kinds of damage of concern (e.g., structural, contamination)
  • Countermeasures considered in response to potential threats and damage
  • The adequacy of current knowledge and available codes and specifications to enable design professionals to retrofit existing facilities and design hardened new facilities

2.3 Prioritization and Risk Assessment

A standardized, objective process is needed to identify those bridges and tunnels that are most likely to be targeted for a terrorist attack and the cost-effective projects to thwart the attack. Prioritization is the process of identifying the likely targets; risk assessment is the process by which methods of defeating the attack will be selected. Both are needed to establish a financial scope (i.e., to determine how much money it costs to deter and provide defense compared to the facility and social cost from the loss) and to allocate available funds appropriately.

Therefore, the BRP advocates both of the following:

  • A prioritization method that could be based on subjective or empirical criteria and is accessible to a wide range of interested parties[13],[14]
  • A risk assessment method that is based on rigorous engineering and mathematical principles accessible to experts and modeled after the methodology used for seismic studies by building on the risk methodology summarized in Section 4 of this report

2.4 Threats

Assessment of vulnerability requires consideration of the means of inflicting damage to a facility, that is, the threat or threats. The analogy to the conventional design process is the identification of the design loads. Effective countermeasures and associated costs cannot be developed without this assessment just as the amount of steel and concrete needed in a bridge or tunnel cannot be calculated if the loads are not known. The following types of threats are considered by the BRP:[15]

  • Low-tech and high-tech conventional explosives (e.g., shape charges)
  • Explosively formed penetrating devices (EFP, kinetic energy penetrators)
  • Low-tech, hand-held cutting devices
  • Truck size/barge size conventional explosives
  • Chemical/biological agents released in tunnels
  • Incendiary conventional explosives
  • HAZMAT release in tunnels
  • Intentional ramming via ship or barge

2.5 Damage

For the purposes of this report, the consequences of attack expressed as damage to bridges and tunnels that are of concern are as follows:

  • Threats to the integrity of the structure (e.g., resulting in replacement of the facility or major repairs)
  • Damage that inhibits the structure's functionality for an extended period of time, such as closure of the facility for 30 days or more
  • Contamination of a tunnel resulting in extended closure or loss of functionality
  • Catastrophic failure resulting from an attack based on the threats described above

2.6 Countermeasures

If the process of prioritization and risk assessment leads to the conclusion that a given bridge or tunnel must be made more secure, there are a variety of countermeasures that can be used singly or in combination to reduce attractiveness and/or vulnerability, or to reduce consequences if an attack occurs. Countermeasures are often grouped into actions or technologies to deter attack, deny access, detect presence, defend the facility, or design structural hardening to minimize consequences to an accepted level. Because of its expertise, the BRP dealt primarily with the last category of countermeasures. The panel's focus does not imply that other strategies for deterring, detecting and denying, or defending are not valid options. In many cases, risk assessment as recommended here will lead to the conclusion that one or more of the non-design countermeasures is the most appropriate and cost-effective solution for a given facility. There are relatively mature technologies and strategies currently available for implementation. Application of these countermeasures still requires enabling funding but not necessarily the research and analysis commitment necessary to develop and implement effective design countermeasures. For completeness, a list of possible low-cost immediate actions to increase security exposure has been collected from several such sources and is appended here.[16]

2.7 Codes and Specifications

Considering consequences focuses attention on the ability to deal with the structural engineering ramifications. Some engineering guidance is available within the Department of Defense (DOD). However, the panel has determined that current design codes and specifications leave much to be desired in terms of how to employ hardening design, how to quantify blast-related demands, and how to determine the capacity of components exposed to high-pressure transients.

Research agenda to fill in the gaps in current understanding of phenomena and response have been developed and are contained in Section 4. Given this basic knowledge, practical comprehensive design guidance and specifications can be developed as outlined here.


[13] These criteria should represent a consensus among stakeholders as to what makes a facility "important" in terms of an agency's mission. In his April 1, 2003, testimony before the National Commission on Terrorist Attacks Upon the United States, G.L. Dillingham of the General Accounting Office states "A criticality assessment evaluates and prioritizes assets and functions in terms of specific criteria, such as their importance to public safety and the economy. The assessment provides a basis for identifying which structures or processes are relatively more important to protect from attack. As such it helps managers to determine operational requirements and to target resources to the highest priorities, while reducing the potential for targeting resources to lower priorities."

[14] The BRP recognizes that the AASHTO Guide to Highway Vulnerability Assessment for Critical Asset Identification and Protectionis the current methodology and acknowledges it as a starting point for prioritizing bridges and tunnels; however, prioritization of bridges and tunnels requires more specific criteria and methods, such as those recommended later in this report.

[15] Recognized experts from USACE presented background information on many of these types of threats to augment the knowledge within the panel.

[16] See Appendix B for a list of commonly used operational security measures that fall into this category of countermeasures.

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Updated: 07/31/2013
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