Birmingham Water Works Board (BWWB) of Birmingham, Ala., has consistently achieved the rating of the number-five water system in the United States...
Blue Ribbon Panel exposes terrorist threat to bridges and tunnels in U.S.; offers a plan of action
When Al Qaeda is in hiding, its yellow streak becomes an escalating threat.
Highlighted in training manuals everywhere are the goals and missions of the terrorist group, and one particular message sent a chilling warning to the U.S. bridge community. It stressed the importance of “gathering information about the enemy and blasting and destroying bridges leading into and out of cities.”
The half-line of intelligence came through bold and clear for the Federal Highway Administration (FHWA) and the American Association of State Highway & Transportation Officials (AASHTO). The two joined together to form the Blue Ribbon Panel (BRP) consisting of bridge and tunnel experts from professional practice, academia, federal and state agencies, and toll authorities, which convened to examine bridge and tunnel security and to develop strategies and practices for deterring, disrupting and mitigating potential attacks.
Their report, released in September of 2003, did not attempt to dodge any truths.
“Among the 600,000 bridges in the United States, preliminary studies indicate that there are approximately 1,000 where substantial casualties, economic disruption and other societal ramifications would result from isolated attacks,” the report stated. “Additionally, the U.S. transportation system includes 337 highway tunnels and 211 transit tunnels; many are located beneath bodies of water, and many have limited alternative routes due to geographic constraints. The BRP recommends prioritization of these bridges and tunnel assets, followed by risk assessment as a guide for allocating federal and state funds to address security concerns, and then implementation of cost-effective operational security measures and engineering design standards to reduce the vulnerability of high priority bridges and tunnels to terrorist attacks.”
The BRP also documented the cost of such a terrorist strike. The ordinary cost of construction to replace a major long-span bridge or tunnel on a busy interstate highway corridor in the U.S. may be $1.75 billion. The panel of experts, however, noted that reconstruction following major earthquakes suggests expediting replacement can double the cost of construction. Furthermore, during the five years estimated for reconstruction the socioeconomic loss to the region resulting from losing as many as 14 interstate highway lanes for an extended period is many times the replacement of the facility.
Several recommendations came out of the BRP report. This article focuses on two areas—planning, design and engineering and countermeasures.
Blue Ribbon’s red alert
In order to prepare for a terrorist event, the prioritization process becomes essential. The BRP believes a “process is necessary for prioritizing all bridges and tunnels with respect to their vulnerability in terms of their criticality of the ability to deter, deny, detect, delay and defend against terrorist attacks.” The panel suggests the development of an assessment model to serve as a framework for evaluating alternatives for thwarting an attack.
Agencies already have prioritization methods in place. AASHTO’s version uses a set of critical asset factors to identify assets that are important to achieving an agency’s mission. It assesses the vulnerability of these critical assets to terrorist attack based on target attractiveness, accessibility and expected damage.
The Transportation Security Administration determines relative risk as a function of relative target attractiveness, relative likelihood and vulnerability.
According to the BRP, a large number of bridges and tunnels lends itself to a two-tier approach: prioritization and risk assessment. Prioritization is usually done in two steps. The data-driven approach ranks bridges by using common criteria based off data supplied by the National Bridge Inventory. The second step of prioritization calls on owners and operators familiar with specific characteristics of the facilities and the services they provide to come up with additional data.
This first-tier ranking is based on the following:
The second tier, risk assessment of high priority bridges, is based on the first tier to determine vulnerabilities and evaluate countermeasures to discourage an attack and mitigate damages. According to the BRP, the risk (R) is determined following an approach similar to the one used for seismic retrofit (R=OxVxI).
The occurrence factor is hazard oriented and will change with the nature of the hazard. It approximates the likelihood that terrorists will attack the asset and includes target attractiveness, level of security, access to the site, publicity if attacked and the number of prior threats. Input into the factor typically comes from the law enforcement and intelligence communities.
Vulnerability is an indication of how much the facility or population would be damaged or destroyed based on the structural response to a particular hazard. It serves as a measure of expected damage, outcome of the event, expected casualties and loss of use. Input usually comes from engineering analysis and expertise.
Importance is a characteristic of the facility. It is an indication of consequences to the region or nation in the event the bridge or tunnel is damaged or destroyed. Input into this factor usually comes from owners, operators and users.
In addition to recommending a state identification and prioritization of bridges and tunnels, the BRP suggested a federal re-prioritization for federal funding based on the following:
Near-term (3-6 months)
Using the FHWA-endorsed methodology, states should prioritize their bridges and tunnels and submit lists of their most critical structures to FHWA.
FHWA and AASHTO should guide the development of an immediate, near- and mid-term cost-benefit methodology based on probabilistic risk assessment for implementing countermeasures. Within the framework of this risk assessment adopted from seismic retrofit programs, consideration should be given to existing methodologies.
Mid-term (6-12 months)
States use the risk assessment methodology to develop a countermeasure plan using a cost-benefit ratio as a metric and provide costs for implementing countermeasures for each of their critical bridges and tunnels to FHWA.
Long-term (12-18 months)
Non-state DOT bridge and tunnel owners begin implementing countermeasures consistent with federal security standards using appropriate funding sources.
FHWA and AASHTO develop and implement modifications to existing bridge and tunnel inspection programs to evaluate conformance to federal security standards.
States implement countermeasures when funding becomes available. One source recommends an initial sum of at least $1.5 billion to address immediate security measures.
When looking at design criteria, owners can mitigate the threat by preventing terrorists facility access; mitigate the consequence effect which would in turn lessen the effect from an attack; or apply both options. The BRP report contains the following examples of approaches to mitigate threats and consequences.
Approaches to mitigate threats:
Approaches to mitigate consequences:
Add design redundancy. Great redundancy among structural components will help limit collapse in the event of severe structural damage from terrorist acts; and
Structural retrofitting and hardening priority should be assigned to critical elements that are essential to mitigate the extent of collapse. Secondary structural elements should be dealt with to minimize injury and damage.
The BRP also calls for the development of an accelerated response and recovery plan, one that maps out alternative routes and evacuation procedures.
As you can see, prevention is the key to thwarting any and all types of terrorist attacks. The BRP study outlines several countermeasure options, including measures covering planning and coordination, information control, site layout, access control and retrofit. While all five areas are important, the BRP did offer a number of retrofit options which every owner should evaluate. Keeping terrorists away from a bridge or tunnel is the first line of defense, but the stronger the structure, the less chance of catastrophic consequence if an attacker does slip through surveillance. The BRP list of retrofit options is: