Risk Analysis/Assessment

Risk Assessment

In the context of transportation, risk assessment answers the following three questions:

• 1.
  What disruptions can occur?
• 2.
  What are the chances that serious events can occur?
• 3.
  What are the health, ecological, and economic consequences if the events occur?

Analysts create scenarios, such as a major bridge failure, a leaking tank car, or a terrorist attack on a train or a rail station. They use event or fault trees to build out risk assessment scenarios. Event trees begin with the event and follow it through each stage, whereas fault tree analyses start with an end state and work backward to identify the event or sequence of events that triggers the most serious consequences.

In the case of short-term signal and power failures, and other short-term problems, the likelihood of an event can be estimated from historical records or expert experience. When there is no historical record, such as a major bridge failure or a terrorist attack, the event is assumed as a given.

Death is at the top of the consequences list, followed by injuries, psychological distress, ecological destruction, and economic impacts. For example, a research team simulated the consequences of [Page 1160]a bridge failure of one-year duration and an industrial accident that sent a lethal plume of chlorine into the environment.

Researchers can measure the immediate and local impacts of a bridge failure by estimating how many people and how much cargo was halted and for how long, and how much physical damage there is to the rail system, as well as any injuries and fatalities. What they cannot as easily estimate is how many people will lose confidence in the rail operations, and consequently drive to work, and how many business owners will shift their operations if too many serious events occur with long-term regional consequences. It is also difficult to readily assess the length of the impact.

For example, the terrorist attacks in the United States on September 11, 2001, that used commercial aircraft, and the London subway bombings in 2005 dampened public use of these modes for many months. Risk assessors, in short, estimate the likelihood of specific events and assess their consequences as the impacts ripple across the landscape and through time.

Risk Management

The focus of risk managers is to determine what to do to eliminate or reduce the consequences of a damaging event. Managers answer three

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