
146 ◾ Risk Assessment and Security
Table 4.11 Threat Assessment for Pipelines, Tunnels, Rail, and
Transit Systems
Threat Assessment (Three Methods)
1. Numerical ratio method: This estimate can be based on historical data,
intelligence information, or various assumptions
a. Let T = number of attacks attempted on the United States
b. Assuming the probability of attacking (some of the) pipelines, tunnels,
rapid rail, and transit systems is equal to all other 18 sectors
c. Probability (P) = T/18 for terrorist attacks
d. Assuming based on the data, there are W facilities
e. Let W = 30,000 system facilities; P = (T/18)/30,000 ∼ 0.00000185 ...