| Agent | An evacuating vehicle or a pedestrian group |
| Agent-level | Agent-level simulation refers to viewing results down to the vehicle or evacuating group level. |
| Alternative | The combination of parameters that make up a simulation's computations: input data sources, warning issuance times, destination locations by Emergency Planning Zone, and various other parameters (e.g., fatality rates, stop-and-go-speed). |
| Binary heap data structure | An efficient data organization method. |
| Break away density | The point at which vehicles transition from free-flow speeds to congested conditions and shift to a Greenshields model for speed and density relationships. |
| Census feature class code | A three-character system that is used to define feature data of roads. The first character denotes roads, the second character denotes road type, and the third character further defines the road type. They are used in LifeSim to define attributes of roads that affect transportation. |
| Consequences | The outcome of an event, including immediate, short- and long-term, and direct and indirect losses and effects. Losses may include human casualties, monetary and economic damages, and environmental impact, and may also include less tangible and therefore less quantifiable effects, including political ramifications, decreased morale, reductions in operational effectiveness, or other impacts. In this manual it is used to describe life loss, and economic damages. |
| Construction type | A description of building method and materials. Construction types are the default parameter used to define stability criteria for a structure. Examples include "Wood Anchored" and "Engineered." |
| Cumulative evacuation outflow | The cumulative count of people that mobilize and reach safety over time. |
| Damage category | A damage category is the first aggregation level for structures; it describes a broad group of structures with shared characteristics. Examples include "residential" and "commercial." |
| Daytime first alert function | This function represents the percentage of the population which will receive a first alert over time during daylight hours, beginning at the time the warning is issued. |
| Destination location | A location within the flooded area that is considered a haven for evacuees or locations outside the flooding extents. |
| Emergency planning zone | An area with potentially unique overall evacuation effectiveness such as evacuation preparedness, community awareness, and types of flood warning systems available. |
| Entities | Organizations/agencies and people responsible for completing actions during a warning and evacuation timeline |
| First alert diffusion curve | A representation of the rate at which the first evacuation warning (first alert) is received (% of population warned over time) throughout an emergency planning zone, starting at the Warning Issuance Time. |
| First alert function | This function represents the percentage of the population that receives an evacuation warning (first alert) over time. They are developed for day and night scenarios. |
| First hydraulic time step | The date and time of the beginning of the hydraulic model simulation (defined external to HEC-LifeSim). It is used in reference to the input hydrograph and defining the hazard occurrence time. |
| Fording depth | The maximum depth a vehicle is willing to ford a road, as defined by the willingness to enter flooded roads functions. |
| Free flow speed | The speed at which vehicles will travel when unimpeded by other vehicles |
| Greenshields Power Term | Parameter used to help define the relationship between speed and density of vehicles on the road network. |
| Hazard | A natural or man-made event that threatens to overwhelm and injure life and/or property, e.g., a flood, toxic plume, or wildfire. |
| Hazard communication delay | The period of time from imminent hazard identification to notifying the agency responsible for ordering an evacuation |
| Hazard occurrence time | The time that the hazard begins to occur. Defined by out of bank flooding or breach formation, for example. Known as the imminent hazard time in previous versions of HEC-LifeSim. |
| HEC-DSS | A database system designed by USACE HEC to store and retrieve scientific data that is typically sequential. |
| High clearance vehicle | A vehicle that has an elevated chassis (e.g., SUV, truck, van, large CUV) |
| High hazard zone | A determination of high risk to life based on the worst conditions an evacuating group is exposed to. The high hazard zone is denoted by hydraulic conditions that cause loss of stability (of a structure, person, or vehicle). People caught in the high hazard zone have a high probability of losing their lives. |
| Imminent hazard identification (ID) time | The time when a person recognizes a hazard, e.g., a dam breach, is very likely to occur and may threaten people such that an evacuation is necessary. The ID time may come after some monitoring and engineering analysis or by observation of the hazard already occurring. |
| Jam density | The theoretical density when traffic flow begins to approach zero |
| LifeSim study | A combination of data, models, or events required to analyze a specific geographic area. |
| Limited Mobility | People whose physical capabilities limit their movement to the roof or attic of a structure. |
| Low clearance Vehicle | A vehicle that rides low to the ground (e.g., sedans, coupes, minivans, small CUV) |
| Low hazard zone | A determination of low risk to life based on the worst conditions an evacuating group is exposed to. The low hazard zone is denoted by hydraulic conditions that typically do not cause loss of stability (of a structure, person, or vehicle) but people are still exposed to potentially life threatening conditions. People in the low hazard zone have a low (but non-zero) probability of losing their lives. |
| Mobilization | Protective action initiation; start of evacuation process. |
| Monte Carlo | A subset of computational algorithms that use the process of repeated random sampling to make numerical estimations of unknown parameters. |
| National Structure Inventory (NSI) | A database of structure locations and attributes developed using information from FEMA's Hazus database and other sources. NSI is currently available only to USACE users. It contains information on structure occupancy type, population, structure values, foundation height, construction type, and other information. |
| Nighttime first alert function | This function represents the percentage of the population which will receive a first alert over time during nighttime hours, beginning at the time the warning is issued. |
| Non-Evacuation Depth | Occupants of a structure can evacuate via a flooded road, unless the closest road exceeds the non-evacuation depth. |
| Occupancy type | A class of structures that incorporates a description of the primary use of the structure and how the structure is occupied. One example is "residential, 2-story, no-basement." |
| Performance (System) | Ability to meet functional requirements. The performance of an item is described by various elements, such as flood protection, reliability, capability, efficiency, and maintainability. Design and operation affect performance. |
| Population at Risk | Generally, population at risk refers to the population subject to inundation during a flood. In HEC-LifeSim, it is calculated as the total number of occupants within structures subject to inundation at the moment when the warning is issued by the emergency manager. |
| Protective Action Initiation (PAI) function | This function represents the percent of the population that takes protective action over time, beginning at the time the first alert is received. See also: Mobilization. |
| Puddle depth | The minimum depth in the "willingness to enter flooded road" function, used to truncate the uncertainty distribution. It represents a puddle or very shallow depth that all vehicles will proceed through. |
| Representative hydrograph | A single hydrograph representing the hydraulic event. The hydrograph is used to develop the warning issuance and evacuation timing relative to the hydraulic event. |
| Representative hydrograph | A visual aid used to help develop the warning and protective action timeline |
| Risk | Risk is a measure of the probability and consequence of uncertain future events. |
| Simulation | A mathematical representation of the behavior of a system, given inputs and initial conditions. |
| Stability criteria | The depth and velocity threshold for total structure collapse due to a hazard. The threshold is defined by a depth-velocity curve. Stability criteria is generally based on construction type. |
| Stop and go speed | Average speed of vehicles in stop and go traffic conditions. |
| Structure inventory | A set of geospatial points that contain damageable elements (typically structures such as homes). |
| Submergence | A water level at a structure that can affect probability of survival. Based on the submergence criteria at a structure, agents are split into either the high hazard or low hazard zones. |
| Warning Issuance Delay | The time it takes from when the emergency managers receive the notification of the imminent hazard to when a first alert is issued to the public. |
| Warning issuance time | The time at which an evacuation warning is first issued to the PAR. The value for warning issuance time is positive if the warning is issued after dam failure occurs and negative if the warning is issued before failure occurs. |
| Willingness to Enter Flooded Road | A function representing the decision making of an evacuating group in a vehicle when confronted with a flooded road ahead. The function assumes some perception of the depth of flooding and the stability of the vehicle. |
