Infrastructure Interdependencies - - State of Operations

We have all been on a highway where the operational state of the roadway falls into one of three categories - - (1) Normal, (2) Stressed/Disrupted, and (3) Repair/Restoration.  The following are important considerations of infrastructure interdependencies in the context of their state of operations:

• The state of operations of a unit, subsystem, or system at the time of a failure will affect the extent and duration of any disruption or degradation in the service of an infrastructure.  A power failure at an intersection at peak travel times is far different than a power failure at off-peak traffic volumes - - the system will react differently.
• The state of operation of an infrastructure can range from optimal design operation to complete failure with a total loss of service to all users.  You can have some part or parts of a system out of service for repair or maintenance - - as long as the condition does not occur during peak usage period when reserve margins are critically low.
• The timing and sequence of events that cause component failures and infrastructure disruptions are important in terms of the effect as perceived by the user.
• It is necessary to determine, for each infrastructure, which other infrastructure it depends on continuously or nearly continuously for normal operations, which other infrastructure it depends on during times of high stress or disruption, and which it depends on to restore service following the failure of a component or components that disrupt the infrastructure.
• The normal operation of an infrastructure, such as a water distribution system, and the repair of a disrupted infrastructure, such as a damaged natural gas system, generally involve multiple functions - - activities, processes, or operations.  Some of the functions occur sequentially in time, whereas others occur in parallel.  In some cases, such as for repair and restoration operations, there may be large uncertainties about the amount of time needed to successfully complete each step in the repair process.