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CHAPTER 2
CAPTA Development Path
Alternative Approaches
The CAPTA methodology reflects a development path guided by user requirements and current
practice in risk assessment. Candidate alternative approaches that were considered but ultimately
found unusable or unsustainable are summarized below.
Subjective Weighting of Threats or Hazards versus Asset Scoring
Many existing risk assessment methods require extensive weighting schemes to achieve rela-
tive ranking of threats or hazards and assets. These weight schemes are initiated by gatherings of
agency subject matter experts with the institutional knowledge to judge what assets may need
mitigation from what threats or hazards. The process is subjective, with rankings subject to influ-
ence by institutional biases and parochial thinking. Initial efforts of the project team focused on
this type of process but restricted the expert input needed to perform the analysis. This approach
proved to be more complex and to require more data than was desired by the NCHRP project
panel. After discussing this option, the project team and the panel chose to move the approach
towards transparency and objective data inputs, relying on expert judgments as little as possible.
CostBenefit Analysis for Countermeasures
The project team initially sought ways to include an objective costbenefit analysis of candi-
date countermeasures as part of the methodology. This conflicted directly with the panel's and
project team's intentions to keep the model a high-level executive decision tool. A high-level model
such as CAPTA lacks the detailed data for a credible costbenefit assessment. More important,
the effectiveness of countermeasures against intentional attacks is speculative at best because of
the responsive and reactive nature of postulated threats. The project team, therefore, chose to
provide cost information for countermeasures deemed generally useful in countering identified
hazards and threats but chose not to quantify the change in risk associated with specific counter-
measures. This decision was reached with the knowledge that one type of countermeasure, those
applicable to natural hazards, does have quantifiable benefits because frequency and severity can
be derived from actuarial data.
For example, if based upon historical data, a blizzard is likely to affect a geographical area twice
per season on average, the expected number of ticket holders and riders along affected rail lines
can be estimated. Implementing a snow and ice melting system along the track, at a known cost,
can be compared to potential lost revenue, and investments can then be made accordingly. In cases
such as this, the factors needed to perform a costbenefit analysis are known with adequate preci-
sion, including the capital and operating costs, the benefit (in terms of expected revenue recovered),
and the frequency of the event.
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