Exchange Requirement: Horizontal Alignment
Name
Horizontal Alignment
Identifier
er_horizontal-alignment
Change Log
| Date (yyyy-mm-dd) | Action | Author (email) |
|---|---|---|
| 2025-12-09 | Initial draft | AI Generated |
Project Stage
Select the applicable project stage(s); remove rows that do not apply.
| Code | Stage |
|---|---|
| 0 | Portfolio requirements |
| 1 | Conception of need |
| 2 | Outline feasibility |
| 3 | Substantive feasibility |
| 4 | Outline conceptual design |
| 5 | Full conceptual design |
| 6 | Coordinated design and procurement |
| 7 | Production information |
| 8 | Construction |
| 9 | Operation and maintenance |
| 10 | Disposal |
Overview
Provide a textual overview of the exchange requirement under the headings Scope, General Description and Information Description. Keep it non-technical and aimed at an executive audience.
Scope
The scope of this exchange requirement is to enable the exchange of horizontal alignment geometry including tangents, curves, direction of travel, and alignment designation data necessary for design coordination and construction layout.
General Description
Horizontal alignments define the plan view geometry of roadways, forming the foundation for all corridor-based design. This exchange requirement captures the complete geometric definition including straight segments (tangents), circular curves, spiral transitions, and associated parameters such as curve radius, length, and stationing. The information model supports multiple alignment types (centerline, edge-of-pavement, construction baseline) and direction of travel designation.
Information Description
The information exchanged through this requirement includes the following parts:
- Alignment General
- Direction of Travel
- Horizontal Alignment Designation
- Superelevation
- Alignment Coordinates
- Azimuth and Bearing
- Horizontal Alignment Curve Length
- Horizontal Alignment Curve Type
- Circular Alignment
- Spiral Alignment
- Horizontal Alignment Curve Key Stations
- Horizontal Alignment Tangent Length
- Horizontal Alignment Tangent Key Stations
Information Requirements
Preconditions
Before exchanging horizontal alignment information, the following information must be available: Project coordinate system and datum must be defined. Design criteria including minimum curve radius and superelevation standards must be established. Alignment control points and horizontal control survey data must be available.
Parts
A part is a set of information that achieves a specific purpose or function within this exchange requirement (for example: Select Object, Assign To Group, Associate Library Reference). An exchange requirement is expected to consist of many parts.
Repeat the following block for each part.
Part: Alignment General
- Purpose: Provide general alignment identification, description, and classification data for project organization and document management.
Concept: Alignment Classification and Identification
- Purpose: Establish basic identification and classification of the alignment for design coordination and construction documentation.
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Alignment ID | Unique identification of the alignment for reference for vertical alignment, corridor elements, and other roadside components. (Type: STRING, Cardinality: R) |
| Alignment Description | Description of the alignment to further explain purpose and/or location. (Type: STRING, Cardinality: R) |
Part: Direction of Travel
- Purpose: Specify the intended direction of vehicular travel along the alignment for traffic operations, signing design, and construction phasing.
Concept: Travel Direction Designation
- Purpose: Define traffic flow direction to support signing and pavement marking design, traffic control planning, and safety analysis.
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Direction of Travel | The direction in which vehicles are moving on a roadway maybe expressed in terms of cardinal directions (Type: STRING, Cardinality: R) |
Part: Horizontal Alignment Designation
- Purpose: Classify the alignment by type (centerline, edge-of-pavement, construction baseline) and purpose for design coordination and construction layout.
Concept: Alignment Type Classification
- Purpose: Identify the role and application of the alignment within the project design framework.
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Baseline | Baselines are established as straight line segments or curves between known fixed points, generally within the right-of-way. (Type: BOOLEAN, Cardinality: R) |
| Horizontal Control Line | Control for horizontal alignment. The stationing for the roadway is measured along this line. (Type: BOOLEAN, Cardinality: R) |
Part: Superelevation
- Purpose: Describe the purpose of the Superelevation part
Concept: Superelevation Information
- Purpose: Describe the purpose of capturing Superelevation information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| End Normal Crown Station | Refers to the point on a roadway where the typical crown (or cross slope) of the road transitions to a different cross slope, such as when entering a superelevated section. (Type: REAL, Units: Stationing, Cardinality: R) |
| Tangent Runout Length | Tangent runout is the longitudinal distance needed to change from a normal crown section to a point where the adverse cross slope of the outside lane or lanes is removed (i.e., the outside lane(s) is level). (Type: REAL, Units: Feet, Cardinality: R) |
| Level Crown Station | Refers to the point where the slope of a lane being rotated is 0% or level at the end of the tangent runout. (Type: REAL, Units: Stationing, Cardinality: R) |
| Reverse Crown Station | Refers to the point where the slope of a lane being rotated is the reverse of a normal crown. (Type: REAL, Units: Stationing, Cardinality: R) |
| Superelevation Runoff Length | Superelevation runoff is the longitudinal distance needed to change the cross slope from the end of the tangent runout (adverse cross slope removed) to a section that is sloped at the design superelevation rate E. (Type: REAL, Units: Feet, Cardinality: R) |
| Full Superelevation Length | Refers to the point where the roadway is sloped at the design superelevation rate E. (Type: REAL, Units: Feet, Cardinality: R) |
Part: Alignment Coordinates
- Purpose: Describe the purpose of the Alignment Coordinates part
Concept: Alignment Coordinates Information
- Purpose: Describe the purpose of capturing Alignment Coordinates information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Start of Alignment Coordinate X | The initial point located by X coordinate from which the alignment is defined and serves as the reference for the entire alignment path. (Type: REAL, Units: Feet, Cardinality: R) |
| Start of Alignment Coordinate Y | The initial point located by Y coordinate from which the alignment is defined and serves as the reference for the entire alignment path. (Type: REAL, Units: Feet, Cardinality: R) |
| End of Alignment Coordinate X | The final point located by X coordinate from which the alignment is defined and serves as the reference for the entire alignment path. (Type: REAL, Units: Feet, Cardinality: R) |
| End of Alignment Coordinate Y | The final point located by Y coordinate from which the alignment is defined and serves as the reference for the entire alignment path. (Type: REAL, Units: Feet, Cardinality: R) |
Part: Azimuth and Bearing
- Purpose: Describe the purpose of the Azimuth and Bearing part
Concept: Azimuth and Bearing Information
- Purpose: Describe the purpose of capturing Azimuth and Bearing information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Bearing | The measure of a line’s direction with respect to compass directions. The direction of a line is expressed in 90 degree increments within the four quadrants of a compass. They are measured north to east, south to east, south to west and north to west and written with the maximums of each being N 90 E, S 90 E, S 90 W and N 90 W. (Type: REAL, Units: Degrees, Cardinality: O) |
| Azimuth | A measure of a line’s direction based on the horizontal angle measured clockwise from north starting at 0 degrees and measuring towards 360 degrees. (Type: REAL, Units: Degrees, Cardinality: O) |
| Bearing | The measure of a line’s direction with respect to compass directions. The direction of a line is expressed in 90 degree increments within the four quadrants of a compass. They are measured north to east, south to east, south to west and north to west and written with the maximums of each being N 90 E, S 90 E, S 90 W and N 90 W. (Type: REAL, Units: Degrees, Cardinality: O) |
| Azimuth | A measure of a line’s direction based on the horizontal angle measured clockwise from north starting at 0 degrees and measuring towards 360 degrees. (Type: REAL, Units: Degrees, Cardinality: O) |
Part: Horizontal Alignment Curve Length
- Purpose: Describe the purpose of the Horizontal Alignment Curve Length part
Concept: Horizontal Alignment Curve Length Information
- Purpose: Describe the purpose of capturing Horizontal Alignment Curve Length information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Length of Circular Curve | Refers to the distance measured along the arc of the curve from the Point of Curvature (PC) to the Point of Tangency (PT). This length is crucial for determining the geometry and alignment of the roadway. (Type: REAL, Units: Feet, Cardinality: R) |
| Length of Spiral | A spiral is a curve of constantly changing radius. The radius at each end matches the alignment into which it is going. Length of spiral refers to the length of this transition. (Type: REAL, Units: Feet, Cardinality: R) |
Part: Horizontal Alignment Curve Type
- Purpose: Describe the purpose of the Horizontal Alignment Curve Type part
Concept: Horizontal Alignment Curve Type Information
- Purpose: Describe the purpose of capturing Horizontal Alignment Curve Type information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Circular | An arc with a single constant radius connecting two tangents. (Type: BOOLEAN, Cardinality: R) |
| Spiral | A transitional curve where the rate of curvature begins at R = ? (tangent) and gradually decreases to R, which is the curvature of a simple curve. (Type: BOOLEAN, Cardinality: R) |
Part: Circular Alignment
- Purpose: Describe the purpose of the Circular Alignment part
Concept: Circular Alignment Information
- Purpose: Describe the purpose of capturing Circular Alignment information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Central Angle | The angle at the center of radius of a circular arc included between the radii that pass through the beginning point (P.C.) and the ending point (P.T.) of the arc. Also known as the delta angle. (Type: REAL, Units: Degrees, Cardinality: R) |
| Degree of Curvature | the arc definition, a D degree curve has an arc length of 100 feet resulting in an internal angle of D degrees |
| the chord definition, a D degree curve has a chord of 100 feet resulting in an internal angle of D degrees (Type: REAL, Units: DegreesPer100Feet, Cardinality: R) | ||
| Middle Ordinate | mid-point of arc to mid-point of long chord |
| Distance from the Mid-point of Curve to the mid-point of the straight line between the P.C. and the P.T. (the Long Chord) (Type: REAL, Units: Feet, Cardinality: R) | ||
| Long Chord | ‘Long Chord” - Straight line distance from the P.C. to the P.T. (Type: REAL, Units: Feet, Cardinality: R) | |
| External Distance | Point of Intersection (PI) to mid-point of curve (Units: Feet, Cardinality: R) | |
| Radius | A straight line distance from the center to the circumference of a circular curve. (Type: REAL, Units: Feet, Cardinality: R) |
Part: Spiral Alignment
- Purpose: Describe the purpose of the Spiral Alignment part
Concept: Spiral Alignment Information
- Purpose: Describe the purpose of capturing Spiral Alignment information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Spiral Angle | The total angle of deflection between the initial tangent of a road and the common tangent where the transition curve (spiral) meets the circular curve. (Type: REAL, Units: Degrees, Cardinality: R) |
Part: Horizontal Alignment Curve Key Stations
- Purpose: Describe the purpose of the Horizontal Alignment Curve Key Stations part
Concept: Horizontal Alignment Curve Key Stations Information
- Purpose: Describe the purpose of capturing Horizontal Alignment Curve Key Stations information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Curve to Spiral Point | Point of change from circular curve to spiral (Type: REAL, Units: Stationing, Cardinality: O) |
| Station Equation | A point that relates a system of stationing to another system of stationing. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Compound Curve | Point common to two curves in the same direction with different radii (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Curvature | The point where a tangent ends and a curve begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Intersection | The point where two tangents of a circular curve meet. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Tangency | The point where a curve ends and straight alignment begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Spiral to Curve Point | This is the point where a spiral curve meets the circular curve. It marks the end of the transition from the tangent (straight path) to the circular curve (Type: REAL, Units: Stationing, Cardinality: O) |
| Spiral to Tangent Point | This is the point where the spiral curve meets the tangent. It marks the end of the transition from the circular curve to the straight path (Type: REAL, Units: Stationing, Cardinality: O) |
| Tangent to Spiral Point | This is the point where the alignment changes from the back tangent to the entrance spiral (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Beginning | The point where an alignment begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Ending | The point where an alignment ends. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point on Curve | Point on a circular curve (Type: REAL, Units: Stationing, Cardinality: O) |
Part: Horizontal Alignment Tangent Length
- Purpose: Describe the purpose of the Horizontal Alignment Tangent Length part
Concept: Horizontal Alignment Tangent Length Information
- Purpose: Describe the purpose of capturing Horizontal Alignment Tangent Length information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Tangent Length | Length of straight segments of alignment (Type: REAL, Units: Feet, Cardinality: R) |
Part: Horizontal Alignment Tangent Key Stations
- Purpose: Describe the purpose of the Horizontal Alignment Tangent Key Stations part
Concept: Horizontal Alignment Tangent Key Stations Information
- Purpose: Describe the purpose of capturing Horizontal Alignment Tangent Key Stations information
Provide a table with the set of information requirements for each concept. Extend the table as needed.
| Idea | Explanation |
|---|---|
| Station Equation | A point that relates a system of stationing to another system of stationing. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Curvature | The point where a tangent ends and a curve begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Intersection | The point where two tangents of a circular curve meet. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Tangency | The point where a curve ends and straight alignment begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Spiral to Tangent Point | This is the point where the spiral curve meets the tangent. It marks the end of the transition from the circular curve to the straight path (Type: REAL, Units: Stationing, Cardinality: O) |
| Tangent to Spiral Point | This is the point where the alignment changes from the back tangent to the entrance spiral (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Beginning | The point where an alignment begins. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point of Ending | The point where an alignment ends. (Type: REAL, Units: Stationing, Cardinality: O) |
| Point on Tangent | A point on the tangent line that is used in the projection of the tangent line in a forward direction. (Type: REAL, Units: Stationing, Cardinality: O) |