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Publication Number: FHWA-HRT-06-072
Date: March 2006
Multiyear Plan for Bridge and Tunnel Security Research, Development, and Deployment
Section 3: Current Practice and Gaps in Knowledge
The events of September 11, 2001, helped bring into focus the need to protect our highway system against terrorist incidents. Prior to September 11, these threats had always been perceived as minor, and, as such, little attention was paid to designing for security. Although the threat has been realized, there is still a struggle to define strategies and solutions to protect our highways against terrorism.
The larger civilian highway community has had little experience designing transportation infrastructure for security. Currently, our highway design codes and standards do not address loadings that might be experienced from terrorist activities, although research is slowly getting underway to change this. These issues, however, are not uncommon to the military. The military research community has long considered structural vulnerability of key structures in terms of how to attack those belonging to the enemy or how to make their own more resilient against enemy attack. The most complete experience with bridge vulnerability has come from numerous recent attacks of enemy bridges with large air-to-surface, precision-guided weapons. Much can be learned from these experiences; however, we can also reasonably assume that terrorist weapons would not be as sophisticated. Since the Oklahoma City bombing and attacks abroad on embassies, considerable work has also gone into the design of buildings for blast loadings. The U.S. Army Corps of Engineers (U.S. Army COE) has done considerable work in the area of conventional buildings and hardened structures subject to military weapons as well as terrorist attacks. The Department of State has supported considerable work in the area of blast/impact-resistant barrier designs. Technologies from these areas can be expanded to determine the applicability to highway structures.
In addition to bridges, the vulnerability of highway tunnels is an issue. The number of tunnels in the United States is growing because of a public preference for underground structures; the availability of better construction equipment and techniques; and the scarcity of above-ground space, especially in larger metropolitan areas. Highway tunnels are often considered to be relatively invulnerable to blast loadings, although there are major tunnels that may be highly susceptible to damage or collapse from a well-planned terrorist attack. A top priority in evaluating tunnel vulnerability to terrorist attacks is the threat of fire. Today, highway tunnels in the United States are designed in accordance with the National Fire Protection Association 502 Standard for Road Tunnels, Bridges, and Other Limited-Access Highways. Although tunnels are designed for fire, and there are restrictions on carrying explosives or other hazardous materials into tunnels, these restrictions are irrelevant when dealing with terrorist actions. Large amounts of explosives are not easily obtained, but it is a simple matter for terrorists to hijack trucks transporting gasoline or other flammable materials, and ignite them in the middle of a long tunnel. Recent accidents in the Mount Blanc and English Channel tunnels have shown that an intense fire and the resulting smoke can be a major threat in tunnels, can cause heavy casualties, and shut a tunnel down for months. Flammable materials, such as gasoline, propane, methane, propylene oxide, etc., can cause a blast problem similar to high-explosive detonation, in addition to fire.
Although there is a wealth of knowledge to be gained from the military, the national laboratories, and also from the mining industry, etc., this information is pretty much unknown to the owners of our highway infrastructure. The needs assessments highlighted current gaps in knowledge in the areas of structural vulnerability to terrorist events, threat definition, structural loadings produced by these threats, possible attack locations, cost-benefit and risk assessment methodologies, post-event assessment strategies, and the need for rapid repair and restoration techniques.
The ideas put forth during the workshop dealt with the overall transportation system. The need to develop a risk assessment methodology specific to highways was emphasized. Risk assessment methodologies are well developed and have been applied to many sectors for many years. However, there are many new and special aspects to the problem of applying existing methodologies to reduce the vulnerability of highways to attack. An essential input to a risk assessment is the event or scenario being analyzed. In the context of risk assessment of a terrorist or security event, the group felt that there was not adequate understanding of the "real" threats. Gathering and analysis of intelligence has not been a key competency or capability in the highway industry. This points to a need for better communication between those involved in the gathering of intelligence and those performing risk assessments. Validated models and tools, utilizing computer-based simulations, are needed to better analyze and quantify the consequences of and develop countermeasures to these threats. The need to develop improved surveillance and sensing technology to provide the data necessary to support the application of these advanced analysis and simulation tools was also identified as an area where research is needed.
In terms of reducing the risk of the highway system being used as a means to attack, the majority of the ideas from the workshop could be grouped into three areas: (1) surveillance technologies and decision support, (2) application of such systems to cargo or freight tracking with an emphasis on hazardous materials management, and (3) socio-political issues.
Sensing, surveillance, and decision support includes the development and use of sensors and surveillance technologies to detect threats, the integration of such technologies into command and control systems, and the actual use of such systems to reduce the threat of the highway system to deliver an attack and, at the same time, the use of these systems to improve the operational efficiency of the highways to move freight and improve the safety of hazardous materials shipments. There was at least an implied perception that freight movement, cargo, and hazardous materials issues represent the most important way in which the highway systems can be used to deliver an attack. In addition, the linkage of the highway system with the transportation systems of foreign countries is predominantly associated with freight and cargo movement.
As for improving the utility of the highway system to respond to and recover from an incident, the workshop pointed out the need for better transportation management in a crisis situation, fundamental research in traffic flow in a crisis, and ability to communicate effectively during a crisis. Other issues identified dealt with decontamination of highway assets and vehicles after biological, chemical, or radiological exposure, and the need for rapid repair and restoration to have the ability to respond and recover from an incident.
Topics: research, infrastructure, structures
Keywords: research, structures, Security, bridges, tunnels
TRT Terms: research, infrastructure, Facilities, Structures