Glossary

A public road is any road or street owned and maintained by a public authority and open to public travel. [23 U.S.C. 101(a)].

• The term "maintenance" means the preservation of the entire highway, including surfaces, shoulders, roadsides, structures, and such traffic control devices as are necessary for safe and efficient utilization of the highway. [23 U.S.C. 101(a)]
• To be open to public travel, a road section must be available, except during scheduled periods, extreme weather or emergency conditions, passable by four-wheel standard passenger cars, and open to the public for use without restrictive gates, prohibitive signs, or regulation other than restrictions based on size, weight or class of registration. Toll plazas of public toll roads are not considered restrictive gates. [23 CFR 460.2(c)]
• A public authority is defined as a Federal, State, county, town or township, Indian tribe, municipal or other local government or instrumentality with authority to finance, build, operate, or maintain toll or toll-free facilities. [23 U.S.C. 101(a)]
• Public roads include those on Federal lands, such as Indian reservation roads, the Land Management Highway System, forest highways, and Forest Service development roads.

A formally defined point of origin or terminus for an anchor section. Since an anchor point may be somewhat ambiguously defined as the center of an intersection or the point where a boundary crosses a route, the location of an anchor point is typically established through the use of a reference object and statement of distance and bearing from that object to the anchor point.

A formally defined path and length for a route that is used to create a 1D datum for linear referencing. Each anchor section begins and ends at an anchor point.

An application, or application program, is a software program that runs on a computer. Web browsers, email programs, word processors, games, and utilities are all applications. The word "application" is used because each program has a specific application for the user.

The portion of an LRM inventory route leading to an intersection; also known as approach. It is defined by a linear LRM object that begins at a specified distance from the intersection and ends at the outer navigation point of an intersection. In the case of a divided highway, only the directional centerline(s) that take(s) traffic toward the intersection will contain an approach segment. An approach is one of the five objects listed in MIRE for attaching highway safety data. MIRE 2.0 lists 38 potential attributes for each intersection approach; not all are applicable at each intersection.

Asset information models represent geometric, geospatial, non-geometric, and non-geospatial attributes associated with structural assets (e.g., bridge, culvert, retaining wall, noise barrier), pavement assets (e.g., road pavement surface, pavement structure), traffic and safety assets (e.g., guardrail, median, pavement markings and markers, sign, signal), and drainage assets (e.g., pipes, manholes, ditches).

AIM contains data and information of a single asset, a system of assets, or the entire asset portfolio at a level required to support an owner’s asset management system. The information is built progressively over the asset lifecycle stages. AIM consists of graphical, non-graphical, and documentation components as well as metadata.

Management systems provide key information and analysis capabilities to agencies implementing asset management principles, but they do not constitute the whole of asset management. Decisions rendered in an asset management environment are much broader in scope, require substantially more economic analysis, and normally involve more than one kind of asset.

Where roadways are all in the same plane and movement may occur between routes at one or more internal navigation points.

Any characteristic that is represented by a column in a table. A table may have any number of columns (attributes). A record identifier column where each record has a unique value is a mandatory attribute for every table.

An information storage system (commonly implemented on a computer system running database management system) that is the authoritative data source for a give data element or piece of information. The need to identify systems-of-record can become acute in organizations where management information systems have been built by taking output data from multiple source systems, re-processing these data, and then re-presenting the result for a new business use.

A physical element or characteristic along a route that limits its use by specified vehicles. A barrier may be defined by a bridge or overhead structure, which may limit the width, height, or weight of a vehicle that may pass over or under the bridge, or by a traffic regulation. A barrier is represented along an inventory route using a linear LRM instance.

A designated portion of the travel surface that is reserved for use by persons riding a bicycle. A bicycle lane is part of a motor vehicle route and may define navigation points but must not create additional intersection points. An exclusive facility for use by cyclists is a bicycle trail.

Generically, a structure for the conveyance of vehicular or pedestrian traffic across an obstacle; a type of structure. Within the context of the Road Network Data Model and its expected use of the NBI, a bridge is “a structure including supports erected over a depression or an obstruction, such as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet between under copings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening.” A bridge is present on both the route going across (on) the bridge and the one going under it.

A business process is a sequence or flow of activities and tasks that collectively achieve a certain organizational goal (BPMN 2024). Typical business processes at transportation agencies include Planning and Programming, Digital Project Delivery, Traffic Systems Management and Operations, Asset Operations and Maintenance, TDM, Safety Analysis. Each of these business processes have multiple sub-processes. For example, Digital Project Delivery has sub-processes such as survey, preliminary design, final design, letting, construction; and asset operations and maintenance have sub-processes such as: asset inventory management, asset inspections, and asset maintenance.

The process of adding measure values to a route centerline. This is typically done by using a calibrate feature operation in a GIS platform using at least two calibration points, one for each end of the centerline.

A point feature that provides a fixed measure value along a centerline for the purpose of controlling measure location error. A calibration point applies to a single route but may include measure values for multiple LRMs existing at that location. Coincident calibration points may exist at some locations, such as at intersections, where calibration of multiple routes may be needed.

ISO 20524-1 mentions "Planimetric Control Points", defined as Point Features with highly accurate X and Y coordinates. These control points can be used to verify the accuracy of coordinates derived from digitizing processes. The standard also describes "Z Control Points", which include Z-coordinate information for height referencing.

The relationship of two object classes to each other. Cardinality is characterized as one-to-one (1:1), one-to-many (1:m), many-to-one (m:1), and many-to-many (m:m). Cardinality may also mean the direction of increasing measure values along a roadway. The specific meaning of the term at any point in this document can be gleaned from the context.

An individually defined roadway surface. A divided roadway has two carriageways. The HPMS, implementing the ARNOLD Reference Manual guidance (ARNOLD, 2014), requires a separate centerline for each carriageway. The business rules contained herein are consistent with that guidance. Each side of a divided roadway (carriageway) defines its own inventory route, with measure values increasing in the direction of travel on that carriageway. The term directional centerline is accordingly used in this document rather than ‘carriageway’.

A 2D planar (X,Y) or 3D (X,Y,Z) non-planar framework for stating a location by giving the appropriate value for two or three coordinates. 

A centerline is the component of the route network that represents the geometry (alignment) of a route (i.e., a travel path associated with a vehicle, or bicycle, or pedestrian). A single centerline is a geospatial polyline feature that can be used to represent geometry of multiple routes.

Centerlines for creating routes are referred to as Inventory Centerlines

Centerlines not used for creating routes are referred to as topological connectors. There are multiple types of topological connectors.

A path through part of an intersection’s navigation space that is reinforced with physical barriers as a means of positive guidance for motorists. In this Guidebook, a channelized turn movement is represented by a turn segment; i.e., a directional feature provided for travel continuity and improved pathfinding algorithm performance. A channelized turn movement is not an LRM inventory route; it exists only within the navigation space of the related intersection. Channelized turn movements are typically provided for larger scale mapping products.

An attribute of a transportation facility, such as functional class, speed limit, travelway width, and number of lanes; a type of LRM object. A characteristic is cartographically represented by symbolizing or annotating the centerline feature.

A means of expressing an object’s attribute using a vertical list of values stored in a table consisting of rows and columns.

A CDE is a centralized environment that allows for the collection, storage, collaborative editing, review, approval, sharing, and dissemination of digital data models. In typical practice, a CDE is designed and built to share information during the design and construction phases of a project, but ideally the contents of the CDE should not be limited to assets or objects created in a BIM or CAD environment. The models and documentation stored in the CDE can include both geometric and non-geometric information about assets from all the asset lifecycle phases.

From the perspective of data management, components are used to capture additional level of information corresponding to each dimension.

For management of routes data, following components have been presented: centerline source and accuracy, travel mode, centerline quality, centerline match points, route referents, route identifier, route measure methods, route measure direction, route concurrency, route network gaps, route attributes, route temporality, route metadata, route topology, connectivity and routability. These components can be used to structure and manage the data in the routes data model.

CADD is the process of creating computer models defined by geometric parameters. The models represent a part or a system of parts that can be changed by adjusting the parameters.

Route concurrency is defined as a road data modeling scenario when multiple routes travel over the same section of roadway. When a concurrency scenario happens, one route is designated as dominant, and the other(s) are subordinate. All the routes participating the concurrency are referred to as concurrent routes.

A point where two (or perhaps more than two) travel paths cross each other.

A defined framework for stating the position of objects relative to each other using at least two location references (X,Y). There are geographic and projected coordinate systems.

The end of a roadway with an optional area for vehicles to turn around. The terminus object class includes an attribute for describing the additional pavement area available for vehicle maneuvering stated as a radius from the end of the centerline. If the roadway terminus is a dead end without additional pavement width, then the cul-de-sac radius will be zero.

A data asset refers to a dataset that is managed at an enterprise organization and used as an asset to support one or more of enterprise business processes by users.

An electronic data delivery system is a dynamic and interactive data dissemination system that provides access via a computer network (such as the internet or network) to certain data.

The accountability for the management of an organization’s data assets to achieve its business purposes and compliance with any relevant legislation, regulation, and business practice, by establishing decision-making structures and prioritized investment in activities to develop enterprise data standards.

A data hub is a centralized service that connects all IT systems, whether they be Web applications, IoT devices, software as a service solution, or core business platforms, such as CRM or enterprise resource planning. A data hub manages the connections to each of the systems and orchestrates the data flow among them.

The planned and controlled transformation and flow of data across databases, for operational and/or analytical use. Data integration can involve multiple steps including access and extraction of data from source systems, validation and cleansing, transformation to a target structure, and finally, loading into the target repository.

A single repository of different databases held in native form, which is typically used for data exploration rather than routine analysis.

The ability to read, write, and communicate data in context, including an understanding of data sources and constructs, analytical methods, and techniques applied, and the ability to describe the use case, application, and resulting value. It is an underlying component of digital dexterity — an employee’s ability and desire to use existing and emerging technology to drive better business outcomes.

Data management encompasses defining data, creating data architecture, modeling data, collecting or gathering data, processing data, storing and securing data, ensuring the quality of data, defining reference data, documenting metadata, ensuring data integration and interoperability, performing document and content management, designing and implementing data-warehousing solutions, and maintaining business intelligence.

Data modeling is the process of creating, storing, checking, updating, sharing, integrating, and exchanging data models during the planning and programming, design, construction, and operations and maintenance phases of asset lifecycle. Some of the open data modeling standards, guidelines, or specifications used for building information models in transportation include: USRS, ARNOLD, MIRE, HPMS, NBI, NBE, BME, bSI’s IFC, OGC’s InfraGML and CityGML. These are extensible data modeling strategies, i.e., they can be extended to incorporate additional objects and their attributes (properties). Data modeling is one of the many aspects associated with data management and is critical for managing data in GIS.

Data pipeline represents the set of transformations that are performed on data that are extracted from a source system. Each of the transformations in the pipeline are referred to as nodes, which receive data and output transformed data. Data represents edges in the pipeline and can be batch or streaming data. Transformations are functions that are applied to data for processing it and adding new calculated fields, engineering new data products, doing quality checks. The pipeline starts with pulling data from the source system and ends with loading data into a target system. The series of transformations that are performed in a data pipeline result in a data processing structure known as directed acyclic graphs. Directed acyclic graphs represent the series of transformations performed to the data in the data pipeline. Each pipeline represents a single, potentially repeatable, automated data transformation job that executes the series of data transformations according to the directed acyclic graph. 

Data platforms are used to create, execute (process) and govern data pipelines.

A documented management system that details the quality objectives and controls to be applied during the various phases of asset data collection. Its purpose is to ensure quality in all work processes, products, and outputs, and to support continuous quality improvement. Management sponsorship and governance are critical to ensuring the success of the plan.

The data supply system is a lifecycle for data that propagates and procures data on behalf of the corporation. Look at data as being bigger than the platform, for enterprise data, this goes beyond the data warehouse. Enterprise data as an asset on behalf of the agency. What the data supply system does is look at data, the inputs, and outputs of data across the agency, across systems, across platforms, across organizations and really manages it as an asset.

Data transformation is a data management activity involving changing a data model using a certain object-type library (OTL) and a certain set of terms and definitions into a different data model using a different OTL and a different set of terms and definitions.

The process of converting volumes of data from one format to another and performing value lookups or substitutions from the data during the process. Translation can also include data validation. This is an important component of a well-executed data lifecycle management program.

An integrated, centralized decision support database that stores cleansed and standardized data from a variety of operational sources to support analysis and reporting.

A data model establishes the geometric, geospatial, non-geometric and non-geospatial data (referred to as attributes) that are managed in a digital data system. A data model is used to represent the structure and relationships of data elements that describe the real world. Data elements refer to the attributes or properties of highway infrastructure assets. The attributes can be graphical (geometric or geospatial) or non-graphical (non-geometric or non-geospatial). The dimensionality of a data model determines the type of asset data that is captured in the model. One-, Two- and three-dimensional models contain data elements representing an asset’s design and geometry in one to three dimensions; 4D models contain data elements describing construction and maintenance scheduling for an asset; 5D models contain data elements providing detailed quantity and cost information about an asset and its components; 6D models contain data elements associated with the lifecycle of an asset and its components; and so on. Two- and three-dimensional models contain data elements that represent asset design and geometry (in 2D/3D); 4D models contain asset construction and maintenance scheduling data elements; 5D models contain detailed quantity and cost of asset and its’ components; and 6D models contain data elements associated with lifecycle of asset and its components.

A set of rules and reference points that are used to establish the surface used by a coordinate system. AEGIST Guidebook (2019) discusses three datum types:

• Cartesian – A 2D planar (x,y) or 3D (x,y,z) non-planar framework for stating a location by giving the appropriate value for two or three coordinates.
• Linear – The 1D reference framework for controlling the production of LRM positions (derived from ARNOLD Reference Manual, September 2014, p. 41). Each inventory route creates its own linear datum. Positions along a route are determined by distance from an origin, as that distance is measured along the path of the facility. A linear datum may be formally defined by a State through anchor points and anchor sections.
• Temporal – A datum based on units of time with a beginning point and possibly an ending point. The proposed NRBM data structure is bi-temporal in that it tracks two time datum, one for the validity period of information in the database and another for the time when changes are made to the database. LRM-based data in the NRBM has one spatial dimension and two temporal dimensions.

That portion of an LRM route leading away from an intersection; defined by a linear LRM instance contained within the navigable space of the intersection. Note that a given portion of a route may serve as both an approach segment and a departure segment. Departure segment is not a MIRE 2.0 entity.

Data stored in an electronic format that may have been in an analog format. For example, taking a printed plan sheet and providing as a digital pdf document.

A virtual representation of real-world entities that synchronizes lifecycle data and processes at a specified frequency and fidelity (Digital Twin Consortium). For infrastructure, this typically has been used to describe full lifecycle and operation and maintenance use of digital data.

Digitalization involves creating a digital version of an analog or physical thing like a paper document, microfilm image, photograph, or sound. Digitalization’s purpose is to create systems-of-record or engagement. Digitalized business operations, business functions, business models and processes, and business activities have been enabled, improved, and transformed by leveraging digital technologies and broadly used and contextualized digitized data, and turned into actionable knowledge, with a specific benefit in mind. Automation is a large part of creating digitalized processes.

Digitization involves managing data and information like text, pictures, graphics, and tables in a digital format for easy processing by a computer.

Dimension can be used in two contexts: (a) data modeling (b) data management. From the perspective of data management, dimension refers to the various data assets in an enterprise data asset inventory. In this guidebook, enterprise data management guidelines are provided for data assets such as: Routes, Intersections, Interchanges, Asset Types and Projects. These are presented as four data management dimensions.

ISO-20524 describes divided highways or Dual Carriageways as two physically separated single-carriageways, each of which represents a travel direction. Divided Highway or Dual Carriageway is a multi-lane facility with a curbed or positive barrier median or a median that is 1.2 meters (4 feet) or wider; also known as, divided roadway or divided facility. A Divided Highway is represented by directional centerlines.

The range of valid values for a given attribute. A domain may be a list of valid choices or a range of numeric values.

The process of calculating the location of LRM instances along a route. The inputs to dynamic segmentation, commonly abbreviated as 'dynseg', are an LRM instance table and a route centerline after it has been calibrated to match the LRM used in the LRM instance table.

A component of the transportation facility, such as a bridge, sign, or guardrail; a type of LRM instance. An element may be cartographically illustrated using symbology applied to the route centerline or by using its own independent geometry.

From the perspective of data management, elements are used to capture additional information corresponding to each component. Data elements are used to structure and organize the data captured in a data model under each of the data components associated with a data asset or dimension. Depending on the dimension and component, elements can be object types, attributes, property sets or properties.

For example:

• In ISO-20524, an "Element" refers to any object within a Geographic Data File (GDF), regardless of its dimensionality or complexity. This includes basic geometric primitives like Nodes, Edges, and Faces, as well as higher-level features like points, lines, belts, areas, and complex features.
• ISO-19148 defines “Element” in the context of linear referencing systems, as any linear object that is being measured. Examples of such linear elements include roads, routes, tracks, rails, and pipelines. This standard considers the concept of "Element" in LRMs is crucial for defining locations relative to these linear features using measurements along their length.
• Within spatial modeling frameworks like Industry Foundation Classes (IFC), an "Element" is an abstract entity used to represent various components of a built environment. "IfcSpatialElement" is a specific type of element that generalizes components used to define the spatial structure and zones of an asset or a project. AASHTO defines Model Elements in a similar context, to establish all the different elements that are associated with a highway facility. The Joint Transportation Committee of Engineering and Electronic Standards has developed a specification for the Model Elements Breakdown (MEBs) to represent geospatial elements.
• From a data science perspective, "Element" takes on a more abstract meaning within set theory and data type definitions. An "Element" in this sense refers to a member of a set, which is an unordered collection of items of the same data type. The concept of "Element" helps define data structures and constraints within data models.
• In MIRE, “Element” is used to refer to properties associated with objects or data assets like road segments, intersection/junction, interchange, horizontal and vertical curves. In HPMS, these road segment properties are referred to as “Events” or “Data Items”.

Data that are shared by the users of an organization, generally across departments and/or geographic regions. Because enterprise data loss can result in significant financial losses for all parties involved, organizations should spend time and resources on careful and effective data modeling, solutions, security, and storage.

A set of interconnected components that has been designed to fulfill a particular function without further human design input. Technological systems transform, store, transport, or control materials, energy, and/or information for a particular purpose.

A graphical means of describing object classes and their relationships to form a data structure. ERDs come in a variety of forms, but typically object classes are rectangles and relationships are lines connecting related object class rectangles. The object class rectangles may contain only the name of that class in a conceptual data model or be expanded to include the names and descriptions of the included attributes, along with specified behaviors and interfaces in a physical data model. ERDs are a means of expressing the organization of data and behaviors within an application but do not necessarily represent the actual structure of the data in that database. As used herein, ERDs do not include behaviors and interfaces; they serve only to express the organization of data.

Extract, transform, load is a data management activity involving extracting data from a system, transforming the data from the format used by the source-system object model to the format used by the target-system object model, and loading the data into the target system. Sometimes the data are transformed after they have been loaded into the target system. In such cases, the term, extract, load, transform is used to describe the data processing operation. 

A geometric object used for cartographic display in a GIS. In a vector object class, features can take the form of a point, line, or polygon defined by vector graphics. Some features may be multipart objects. Centerlines, calibration points, navigation points, and element geometry are all features.

A group of features having a common definition and treated as a cartographic layer of similar objects that may be added or removed from a dataset using a single action.

The intersection of a row and a column in a data table. Each field stores a value describing an attribute of the object. These values are constrained by the attribute definition, such as the data type or maximum number of alphanumeric characters and may additionally be constrained by a stated domain of valid values.

The cartographic feature created to represent an entity in the database. All geometries supported in this Guidebook are vector graphics; they include point, line, and polygon and may be multipart. Geometries are abstract and cannot reflect all aspects of the entities they seek to represent.

A tool used to create, manage, analyze, and map all types of data. GIS connects data to a map, integrating location data (where things are) with all types of descriptive information (what things are like there). This provides a foundation for mapping and analysis that is used in science and almost every industry. GIS helps users understand patterns, relationships, and geographic context. The benefits include improved communication and efficiency as well as better management and decision-making.

A random 32-digit hexadecimal number that has a very small chance of being duplicated. A hexadecimal number is one using Base-16, where the decimal digits of 0-9 are supplemented by the capital letters A-E, which represent the decimal equivalents of 11-15. Counting in hexadecimal, the number 10 = 16 in decimal (Base-10). A GUID contains 128 bits of information. The possible number of GUIDs is 10 to the 38^th power. The 32 hexadecimal digits are grouped into segments of 8, 4, 4, 4, and 12 digits. Most database management systems can generate GUIDs. 

The name given to an object so as to uniquely identify it. In a database, the identifier is called the primary key and may consist of multiple fields.

How agencies manage data and information, and how these data are used.

A single object; a single row in a table.

The act of creating an example of a real-world or conceptual entity, such as an object or a row in a table. 

A  point on one or more limited-access highways where traffic may move from one route to another. An interchange is an inventory route element. Each interchange must include at least one ramp (acceleration or deceleration) and two intersections (both ends of the ramp). MIRE 2.0 lists 25 attributes for interchanges.

The area of the interchange ramp road element features extended by the exit ramp auxiliary lanes/tapers and the entry ramp auxiliary lanes/tapers.

A geometric point feature that is used to represent the general location of an interchange. The location of the interchange is defined by an LRM position for only the limited-access highway, but the actual interchange point feature is not cartographically placed on a route centerline. When more than one limited-access highway is involved at a single interchange, each such highway will have an LRM position recorded for the interchange’s location on that highway. The LRM position description of the interchange is used by many States to create an interchange number within the context of the milepost signage LRM.

The area of the intersection navigation space extended by the length of the intersection legs.

A geometric point feature that represents the general location of an intersection. An intersection point need not be located on an inventory route but its position within the LRM of all involved inventory routes will be recorded as an LRM object. An intersection point defines the end or beginning location of at least two road elements. Turn segments must terminate at a pair of nodes. An at-grade intersection of two or more bidirectional routes has a single node coincident with the intersection point.

An intersection is a junction where two roads cross, merge, diverge, or meet at the same elevation and where vehicles, bicycles, or people can make a choice on traveling direction. It is a navigation space that can comprise multiple nodes and therefore allows for travel choices to be made by travelers. Vehicles, bicycles and/or pedestrians may move from one route to another at an intersection/junction. Intersection is a MIRE-defined object.

Whereby a node or conflict point is part of a larger collective, so all sibling nodes or sibling conflict points know which parent feature of the intersection data model represents them collectively. Example 1: Eight nodes at four locations of a hashtag intersection have a relationship to the Intersection/Junction point that is at the center of that hashtag. Example 2: An intersection inside the influence area of a collection of interchange ramps has a parent feature equivalent to the Intersection/Junction point of the larger interchange.

The BIM forum describes the Level of Development Specification as a reference enabling practitioners in the architecture, engineering, and construction industry to specify and articulate, with a high level of clarity, the content and reliability of their BIM design models at various stages during the design and construction processes.

The 1D reference framework for controlling the production of LRM positions. Each inventory route creates its own linear datum. Positions along a route are determined by distance from an origin, as that distance is measured along the path of the facility. A linear datum may be formally defined by a State through anchor points and anchor sections.

A method that is used to establish location of an asset, road attribute (characteristics), project, work order, work request, inspection or other such event along a road by specifying the route on the road, the begin/end milepoint or mile-marker and the direction. An LRM establishes a means for establishing a position description along a transportation route using a combination of a route identifier and a measure. In most instances, the measure represents the distance from the route’s point of origin to the location in some specified unit of measure, such as miles, feet, or meters. Typical methods used are mile point, milepost, reference point, and link-node. The LRM chosen for the Road Network Data Model is mile point, which means that LRM position measures are stated in terms of a distance, in units of 0.001 miles, from the route’s point of origin, and that the distance between two points on a route is the mathematical difference in the measures defining those positions in the LRM. However, a milepost LRM is typically used for Interstate highways and other limited-access roadways. The milepost values generally begin at a State boundary or signed route origin. Milepost LRMs should also be provided as a separate linear datum.

A rule-based framework for managing and applying LRMs. Such rules include how to calibrate field equipment, the various workgroup responsibilities for each LRM and their use, and the governance structure that manages changes in organizational LRMs. The LRS should align LRM positions in all measures to accurately map information from various business groups utilizing different LRMs.

In an LRS, the travel spaces or paths on a road that are used by vehicles, pedestrians, bicyclists can either all be represented using a single route (i.e., single polyline geometry), or using multiple routes (multiple polyline geometries). For each route that is created in the LRS, the Routes data model includes following information: 

• Route information such as route identification, route name, class, route centerline geometry 
• Nodes: Points at which two routes intersect and therefore serve as decision points for travelers
• Road Elements (Edges or links), which are created by segmenting routes at nodes 
• Route characteristics such as speed limit, functional class, traffic volume, crashes, roughness etc.

The place where an object exists in the real world. An object has one location, but that location can be described by multiple positions.

Any road characteristic, road feature or event that has an LRM-based position description. An LRM object is an example of an LRM instance, which is anything that can be given a location description using linear referencing. LRM objects are those LRM instances that are included in a database. LRM objects come in point (one LRM-based position) and linear (two LRM-based positions) types. Something that happens to or along a transportation facility, such as a vehicle crash, work program project, or maintenance activity; a type of LRM instance analogous to an LRM Object. An event may be cartographically illustrated using symbology applied to the route centerline through an LRM position reference or may be shown using its own independent geometry. If an actual event occurs in more than one location, it will need to be subdivided into discrete LRM objects for each location-specific component.

A description of a location using a linear reference consisting of a defining inventory route identifier, a measure value in whole M units, and, if there are multiple LRMs, an indication as to which 1D reference system applies to the LRM position. An LRM position may be stated as an “at” LRM location using a single measure or as a “from” and “to” LRM location using a pair of LRM measures.

Match points are locations where two networks come together and need to be connected. For example, match points should exist at the end of each route that leaves a state and continues into the next state. Match points may also exist at other jurisdictional boundaries where maintenance of a road changes or where different modes of transportation connect.

A number that represents a position along a route, as defined by the applicable LRM and its 1D reference datum; also known as a route measure. A measure value cannot be stated without also providing the related route identifier and, if there is more than one, the applicable LRM datum. A measure value is not absolute and represents only a relative position found between two calibration points. A measure (m) may be stored for each centerline vertex as one of several coordinate variables; e.g., a GIS software shapefile allows the coordinates of X, Y, M, and Z.

LRM measures are stated in terms of a unit of measure, which is 0.001 mile (5.28 feet). This measurement unit has been converted to integer values and is symbolized by the Greek letter M (mu). LRM measures stated using an integer M-value can be converted to miles by dividing by 1,000; i.e., 1,000 M = 1 mile. Using integer values eliminates the difficulty of working with floating-point decimal numbers and the resulting potential for changes in precision (number of decimal places) between applications. Measure values may continue to be stored using decimal values, but the resulting mathematics will not produce aberrant answers.

Any physical or regulatory barrier, except a single- or double-painted centerline, that subdivides a roadway into directional flows. Median types recognized by the Road Network Data Model include Unprotected, Curbed, Positive Barrier, and Continuous 2-way Left-turn Lane. Each median should be represented in the dataset by a median element with an LRM position defined on the directional inventory route located on each side of the median.

A location along a dividing median where traffic may cross the median and/or execute a U-turn. A median-cut intersection does not subdivide a road element; it occurs along a road element. A median-cut intersection is located on each road element of a divided roadway. A topological connector is not provided to link the two median-cut intersections for use by routing applications. 

A connection from a roadway to another mode of travel, such as a vehicle ferry loading dock. A multimodal interchange point is used when continuity of travel is provided for the same vehicle. A multimodal terminus type is appropriate when the nature of travel requires a change in the transporting vehicle, such as a bus terminal or airport.

The area within an intersection where vehicles and/or pedestrians may select from multiple paths through and out of the intersection. A single intersection may contain only one navigation space. Due to inherent limitations of the LRM concept and the related scale of abstraction, an intersection is a singularity with no internal structure. However, MIRE and other safety and operational analyses must look at the internal structure of an intersection. To meet this need, the Road Network Data Model supports the use of separate cartographic treatments for revealing this internal structure, which may include a navigation space containing navigation points and turn segments for all but the simplest intersections. Intersection analyses may link approach segments to the navigation space.

A node is a point where two routes intersect with each other. ISO-20524 defines a "Node" as a zero-dimensional element that represents a topological junction where two or more "Edges" meet or where an "Edge" ends. This highlights the role of "Nodes" as fundamental building blocks in the topological structure of geographic data. Nodes can be tagged as a Drive node and/or Bike node and/or Walk node, depending on the type of routes that intersect at the node. A drive node is created when two vehicle routes intersect with each other. A Bike node is created when two bicycle routes intersect with each other. A walk node is created when two pedestrian routes intersect with each other. A node also serves as a decision point as it is a point where two routes intersect and travelers could decide about the route they would like to proceed on, i.e., whether they would like to turn left, turn right, or go straight. For this reason, nodes can be used to hold information about turn restrictions. Nodes also serve as the topological termination of an edge or link. ISO-19148 suggests that a "Node" could be used as a referent in a linear referencing system (LRS).

A means of constructing databases and applications in the form of discrete object classes that have defined behaviors expressed to the outside world by one or more interfaces. The internal structure of data and software is not visible to the user. An interface specification describes the inputs to the class, called arguments or messages, and the output of the class, called results. What happens inside the class is called the method. The three principles of object-oriented design are encapsulation, polymorphism, and inheritance. Encapsulation means that everything regarding the data and behavior of the class is inside the class. Polymorphism means that the user can send the same message to two object classes and get different results due to the unique methods of each class. Inheritance means the programmer can create a “child” class from a “parent” class, where the child class inherits all the interfaces and methods of the parent, and then adds new interfaces and/or methods. The creation of a class is called instantiation. A class may be abstract in that it can serve as a concept for a class but is not actually instantiated itself. "People" is an object class. "Person" is an abstract object. “You” are an instantiated object in the People class. What you do is your method. How you interact with the outside world, both in perception and expression, is through interfaces. The memories you contain, and the logic process you use to act in response to inputs are the data encapsulated in your brain. How your body works is not exposed to the outside world; it is encapsulated. You inherited certain data and behaviors from your parents.

An object-type is a data entity that is used to represent the physical and functional elements of a real-world highway infrastructure element in the digital world. An object is described by its attributes or properties, which can include both geometric data, such as the object’s dimensions in space, and non-geometric data describing the object’s characteristics, such as the object’s name, type, owners, and condition. A defined type of object in a database structure; also known as an object class. A class is the representation of a group of similar objects conforming to a shared definition within a data model; i.e., an abstract representation of a group of similar objects that includes defined attributes and may include specified behaviors. In a relational database implementation, a class is a table consisting of rows and columns with behaviors embedded in software that acts on the data.

An OTL lists standard object-type names (e.g., bridge, road, tunnel) and their attributes or properties.

ISO-20524 defines "Point Feature" as a Feature with a single spatial position. This definition establishes "Points" as fundamental elements within the GDF data model, capable of representing various real-world objects with specific locations. ISO-20524 demonstrates the versatility of "Point Features" in representing diverse geographic information. Points serve as building blocks for geometry, reference points for measurements, and discrete locations for features. ISO-19148 specifies a "point" operation that returns a “Geometry::Point” representing the spatial position equivalent to a linearly referenced position. This definition from ISO-19148 implies that Points are spatial features that can be used to represent any linear referenced event or object in the LRS. Therefore, AEGIST defines Points as a geospatial feature that can be used to represent following features in the road network: route calibration points, decision points (nodes), merge/diverge points, grade separation points on interchanges, gore points, traffic conflict points, intersection points, etc.)

A location stored in a database using a description conforming to specified rules. For example, a bridge’s location may be described using geographic coordinates or a route/LRM measure. A position is a relationship between a location and a datum. Time may also be a part of the position description, as in when the object was at this location.

The attribute(s) that are used to define a single instance of an object class. Primary keys are generally generated by the database management software and serve only to define a single object in the class. A single attribute is used to form a simple primary key. Multiple attributes are used to form a complex primary key. All object classes included in this document use complex primary keys to separate records that differ by time but describe the same object. Minimally, both the object identifier and the record date are needed to select a single record.

PIMs represent geometric, geospatial, non-geometric, and non-geospatial attributes of planned, programmed, active, and completed capital and maintenance infrastructure projects. This information may also include unstructured data such as project design documents and plans that are attached and georeferenced to the road or an asset on the road, and project information such as improvement type and improvement dates.

PIM contains information about design and construction aspects of a project or facility. PIM consists of documents, non-graphical data, and graphical information that define the constructed asset(s).

A mathematic process of converting a spherical coordinate system to a planar system, such as may be used to convert locations on the surface of the Earth stated using latitude and longitude values to locations on a flat piece of paper for mapping purposes. Projections typically seek to preserve shapes and/or spatial relationships.

A point of interaction between railroads and other modes of travel; also known as, highway-rail crossing. A divided highway will cause two adjacent intersection points to be created so information about the shared railroad grade crossing may be discovered. 

A special inventory route that represents a path of entry to or departure from a limited-access highway at an interchange. Typically, one end of an inventory route that serves as a ramp will coincide with a ramp junction point feature. The related intersection point feature is placed on the related directional centerline at right angles to the physical gore. The LRM measure for the ramp intersection is determined by this location.

The point at which the inventory route representing the ramp topologically connects to the limited-access highway. The location of the ramp junction corresponds with the ramp’s physical gore. A topological connector links the ramp junction intersection on the limited-access highway to the ramp merge/diverge point terminus for routing applications.

The point where a limited-access highway ramp begins or ends at the physical gore. A topological connector links this terminus to the related ramp junction intersection on the limited-access highway.

A model of a surface where the area of the surface is subdivided into equal subareas, called pixels, that contain the attributes of that subarea. Pixels are arranged into rows and columns. The position of a single pixel is defined by its row and column identifiers.

A physical entity that is represented in a model.

An object stored in the database, such as a row in a table.

In ISO-19148, "Referent" is defined as a foundational concept for relative linear referencing methods (LRMs) that represents a known location along a linear element (e.g., a road centerline) from which relative measurements are taken. ISO- outlines different types of referents, including "Node", "Reference Marker", "Intersection", “Mileposts”, and "Centerline Point". "Referents" enable the expression of locations as distances from these known points, facilitating relative LRMs. ISO 20524 defines a "Referent" as a Point Feature, emphasizing its representation as a specific, locatable point in geographic data.

Software used to store, manage, query, and retrieve data stored in a relational database is called an RDBMS. The RDBMS provides an interface between users and applications and the database, as well as administrative functions for managing data storage, access, and performance.

A requirement refers to a need associated with a use case activity or task that reflects what data are needed and the form and format in which it is needed. Corresponding to each road network data use case, there can be many requirements, and each requirement establishes the need for the type of road data, and the content, form and format of the data that is required to execute the activities and tasks.

A potential impediment to travel. Examples include bridges, tunnels, gates, and time-of-day limitations to travel for all or some vehicles. The routable aspect of topology in the Road Network Data Model includes only physical limitations to travel, such as may be presented by weight limits on bridges.

According to ISO-20524 (Geographic Data Files) and OGC CityGML, roads are physical transportation spaces that are used by vehicles, bicyclists, and pedestrians. ISO 20524 emphasizes the network aspect of roads. It defines a "Road" as a complex feature connecting two Intersections, composed of Road Elements. USRS defines a road as a portion of a highway that includes shoulders, for pedestrian and bicyclists use (in addition to the vehicle lanes). That is, roads are transportation spaces that are used for both motorized and non-motorized travel. ARNOLD reference manual (ARNOLD, 2014) establishes that all public roads need to be modeled and reported to FHWA. Roads refer to all public roads, and depending on administration responsibilities can be further sub-categorized as: State DOT-maintained roads, local, and private roads.

A Road Element is a section of a route between two nodes. It is also referred to as an edge or a link because it connects two nodes (decision points) in the route network data model. Road Elements are created when routes are segmented at points of intersection with each other, i.e., at nodes. They represent the most atomic segments of a road that do not have any entry or exit points for traffic (vehicle, bicycle, or pedestrian). ISO-20524 defines Road Elements as the smallest independent unit of a road network that has a node at each end. A route is a series of Road Elements that have the same route identifier. Furthermore, ISO-20524 emphasizes that road is a complex feature that is composed of multiple road elements. USRS also recognizes road elements and defines them as “a line feature that is terminated at each end by a point feature” USRS considers a line feature to be a sequence of one or more edges, and therefore, road elements as per USRS can be associated with one or more edges. Therefore, AEGIST defines Road Elements as a section of road that connects two nodes, but, can also span one or more nodes along the way.

A road network data or information model contains information about:

• Road: Road information in the model includes geospatial attributes such as road geometry; start/end (mile point or milepost or latitude-longitude); and non-geospatial attributes such as number of lanes, shoulder type, width, functional class, facility type, mobility performance (e.g., traffic volume, counts), safety performance (crash statistics), health performance (e.g., pavement roughness, cracking, faulting), and road surface type.
• Intersection/Junction: Intersection/junction information in the model includes geometry of the intersection/junction and non-geospatial attributes such as identifiers and names of the roads that intersect at the intersection, traffic control type (signalized/unsignalized intersection), etc.

A transportation facility path extending from an intersection to an intersection, from an intersection to a terminus, or from a terminus to an intersection. It is a representation of a road that has attribution that may or may not include geometry. Each road segment needs to be represented by one edge and terminate at two nodes. The ordering of termini defines the topological direction of the road segment. A Road Segment could contain multiple road elements or partial road elements.

Cartographically, a road segment is represented by a segment centerline, which may be part of a directional pair. A road segment is represented in the transportation network topology by an edge. When representing the path of a divided roadway, one or two topological connections may be constructed and added to the end of the road element (as defined by the inventory route’s LRM measures) to the intersection point.

A road segment is related to inventory route and road element as follows:

• • A road segment is an atomic element of an inventory route, i.e., an inventory route consists of one or more road segments. Road segments are sections of a route that are typically created based on certain sectioning or segmentation criterion. For example: 
    • Road Events: These are road segments that are created to collect HPMS sample data and are therefore also referred to as HPMS sample sections. 
    • NG911 Road Centerlines: These are road segments that are created when routes are segmented at nodes, provisional boundaries, county boundaries, or public service answering point boundaries.
    • HPMS Sample Sections: Sections of roadway on the Federal-aid system (excluding Rural Minor Collectors and Local roads) identified by State DOTs based on a statistically random process. Each sample section identifies a location where detailed roadway event data is provided to FHWA for modeling and analysis purposes. 
    • Pavement Construction History Segments 
    • International Roughness Index Segments
    • Rutting Segments
    • Faulting Segments
    • Cracking Segments
    • Pavement Management Sections (Segments): These are road segments that are created after dynamic segmentation is done based on pavement condition, pavement type and pavement construction history. 
    • Maintenance Segments: These are road segments that are created after routes are segmented based on highway maintenance jurisdictions. 
    • Traffic Sections/Segments: These are the traffic AADT segments that are computed based on point location of traffic count stations.
    • Project Sections/Segments: These are segments that reflect the location of active and completed capital projects that are typically maintained in a DOTs project management system and entered FHWA’s FMIS system (for federal-aid projects). 
    • Safety Sections/Segments: Per HSM are Safety sections are segments of road that traverse from one intersection to another. Often roadway characteristics such as number of lanes, urban/rural area, lane width, shoulder width, median presence/absence are taken into consideration for creating safety sections for diagnostic analysis of crash locations. 

Such as needed for a major driveway that has the characteristics of an at-grade intersection but involves only one route. Traffic control, crash instances, and other traffic data are typically provided. Intersections of this type do not automatically break road elements.

Any of several configurations of an at-grade intersection where vehicles operating along a directional rotary may move from one route to another; also known as a traffic circle or rotary. A roundabout will contain multiple internal navigation points and turning segments but is represented by a single intersection point (LRM instance) in the Road Network Data Model. 

The characteristics of a topological network with the ability to determine whether any two points—an origin and a destination—are physically connected by a continuous sequence of road elements. A routable network has the ability to determine whether a path is possible and to identify those road elements that form the path. Travel cost is determined by the length of each road element and (optionally) other user-selected attributes. Travel restrictions, such as bridges and tunnels, may be present on various road elements that can cause them to be eliminated from the transport network prior to conducting the routing analysis. This is the simplest aspect of pathfinding, which includes the ability to provide turn-by-turn directions to a traveler as to how to navigate the network to get from the origin to the destination. Routability depends on the road element choices available at each intersection. As a result, internal components of an intersection, such as navigation points and turn segments, are not included in the routable network. The routing application should be responsive to restrictions present on road elements.

Routes are paths or traversals along a road that are taken by motorized vehicles (personal and transit – bus/rail vehicles) and non-motorists (e.g., pedestrians, bicyclists). Routes can be used to represent the road as they represent the paths that are taken by travelers who travel along the road.

While not directly using the term "Route," ISO-20524 introduces the "Path" Feature. It defines a "Path" as a linear corridor, potentially spanning significant lengths (e.g., hundreds of miles for roads). A "Path" could represent a "Route" or a segment of a "Route."

IFC defines "Route" through the "IfcRoad" entity. It emphasizes the real-world function of a "Route" as a physical infrastructure element facilitating travel. IFC's definition focuses on "Routes" built on land for travel between locations. It includes various types like highways, streets, cycle paths, and footpaths, distinguishing them from railways.

ISO-19148 provides the broader framework for linear referencing, which is crucial for defining and managing "Routes." While not explicitly defining "Route," it establishes the concepts of "Linear Referencing Systems" (LRS) and "Linear Elements." These concepts underpin the definition and management of linear features like "Routes" in a standardized way.

Modeling a route involves establishing (a) Route geometry (b) Route attributes (characteristics) such as route identifier, functional class, facility type etc. and (c) Route Intersections or Interchanges. The geometry of a route is illustrated cartographically using centerlines. On a road, routes can be created to represent vehicle paths, pedestrian and bicycle paths. A Route is a published traversal that follows the path of a linear transportation facility identified by name or assigned route number. A Route is also a series of Road Elements that have the same route identifier.

The use of route nomenclature to determine the names of directional interactions of divided routes that have “root” names that place adjacent nodes into the same family, ergo the same hashtag or semi-hashtag intersection or collection of ramps at an interchange. Example: US-60 EB and US-60 WB both have a “root” value of US-60. US-93 NB and US-93 SB both have “root” values of US-93. There are eight combinations of US-60 and US-93 at a full hashtag intersection (A intersects B and B crosses A at four different locations). If the direction-bound suffixes (NB, SB, EB, WB) are discarded and the intersections are renamed in alphabetical order by route, all eight intersections and four locations will have the name US-60_US-93. The eight node interactions are an “intersection relationship” and their independent X/Y locations or shapes can be averaged to make a parent Intersection/Junction point to represent the complex location as a single point.

A topological representation or model of the routes (travel paths or traversals), the nodes (at which the routes intersect), the road elements (segments of route between two nodes) and match points (locations at which two routes connect). The route network data model is used to store information about the geometry of the routes and the associated attributes that characterize each route.

Gaps are breaks in geometry of a route, which may occur either due to two routes overlapping with each other (resulting in one of the overlapping routes being modeled using a gap), or, due to the route having a gap in the real world (wherein the road that is represented by the route starts and ends at multiple locations). A route may have gaps.

Serves as the outer boundary of a given State’s roadway system.

A data type that allows alphanumeric characters to be used to provide a value given for a defined attribute. The maximum number of such characters is usually specified in parentheses.

People-focused applications that are designed to equip and enable customers, partners, and employees with the tools they need to interact with the business. Systems of Engagement overlay and complement Systems-of-Record and harness any number of technologies including mobile, social, cloud, and big data innovation. They are designed so everyone in an organization can access the information needed to carry out daily tasks more effectively. This systematic approach complements an organization's investment in its larger business systems or systems-of-record. It provides convenient access to relevant spatial data and easy-to-use applications that enable and encourage collaboration.

An organization of data presented as a set of rows and columns. Each row describes a single object. Each column describes a single attribute of such objects. Note that the actual storage of data need not conform to the table structure, which is a means of showing data to a user.

A road element beginning or ending point that is not a roadway intersection.

A geometric point feature that represents the location of a terminus. A terminus point may only be coincident with a single road element.

An event or a portion of a centerline – hence a portion of a route – that exists for purposes of connecting design/survey centerlines that otherwise do not touch each other in the real world. For example, the ramp centerline and the main carriageway centerline (near an egress or ingress opportunity along a roadway) typically do not intersect because engineers designed them to be parallel to each other. They do transmit traffic via parallel lanes which can be traversed by vehicles moving from the ramp lanes to the mainline lines – or vice versa. GIS professionals have developed ways for forcing these parallel centerlines to connect or touch for business purposes. The connections tend to generate double counting of inventory unless the asset modelers take precautions to abridge all secondary route inventories near the edge of the primary route inventory. Some agencies will track topological connectors as events. Others will split them away from longer centerline feature class records and give them a Centerline Type attribute that designates them as a topological connector. In the latter form they are directly editable and useful for pathfinding connectivity because they also have a OneWay attribute for path restrictions. In the former form they can be redacted from inventory to correct inventories against double counting. When intersection legs approach an intersection, the two major legs should be treated as inventory and the remaining legs as topological connectors. If no legs are sub-dominant, then localized rulemaking should be consistently employed.

Within the context of the Road Network Data Model, topology is the connectivity of linear facilities at points of intersection or termination. Topology is provided only for road elements, which may be defined by the path between two intersections or one intersection and one terminus. Topology is not provided for inventory routes or ramp extensions.

The combination of measures that serve to preserve traffic capacity and improve the security, safety, and reliability of the overall road transport system. These measures make use of ITS systems, services, and projects in day-to-day operations that impact on road network performance.

A linear transportation facility devoted to travel by unlicensed vehicles, ridden animals, and/or pedestrians. Trails may be limited to use by pedestrians alone or to specified subsets of motorized and non-motorized vehicles. Road elements and inventory routes may be defined for trails. Trail heads and crossings involving one or more inventory routes should be noted by an LRM object and may define an intersection.

The mathematical process of converting positions from one reference framework to another.

The ability to move traffic from one lane to an adjacent lane. Solid lines indicate lack of transmissibility. Dashed lines allow for transmission of traffic between lanes. Zones of transmissibility are ranges of the longitudinal route that allow movement to any lane that is not protected by a solid line.

The term is principally part of the routes data model and is defined in Chapter 3, Terms. In the intersection data model, the term is used in describing approaches to and departures from interchanges.

The portion of a transportation facility that is intended for the movement of people and/or vehicles. The travel path does not include shoulders but does include bicycle lanes and other portions of the facility dedicated to the movement of designated vehicles.

A logical path through a transportation system. A traversal may be stable, as in the case of a numbered route or named street, or it may be transitory, as in the case of a path used once for a specific journey.

A structure conveying a traveled way beneath an obstacle. In the NBI, a tunnel is recorded as a bridge, with the route going through the tunnel begin listed as being under the bridge.

A path between nodes within a navigation space. Movements along turn segments may be restricted by vehicle type, time of day, etc. Turn segments have no LRM length. Most turn segments are short pathways internal to traditional intersections.

A use case represents a subset of activities and tasks in a business process or sub-process that use road network data. A use case establishes how road network data are used, processed, or manipulated as the activities and tasks associated with it are executed.

An abstraction of entities in the real world using simple geometric objects (features), typically points, lines, and polygons. A point feature is defined by a single set of coordinates. A line and the boundary of a polygon are described using one or more ordered coordinate sets. The actual structure of vector graphics is specific to each vendor, although some general standard methods exist. Typically, the coordinates of the first vertex (origin) in a sequence for lines and polygons is fully stated in terms of the applicable coordinate system and subsequent vertices are stated as offsets from the origin. Some GIS platforms support multipart vector objects. Attributes are associated with each vector feature.

A single coordinate set describing a geometric location in a coordinate system (plural – vertices). A vertex must be stated using all the required coordinate axes. A point consists of a single vertex. A line consists of two or more vertices. The boundary of a polygon must include at least three vertices.