Horizontal Alignment

Child Classes

Property Sets

Applicability

This specification applies to all Horizontal Alignments. It also addresses the child class Horizontal Alignment Curve. It also addresses the child class Horizontal Alignment Tangent.

Child Classes

Horizontal Alignment Curve

This child class inherits the requirements defined for the parent element.

Horizontal Alignment Tangent

This child class inherits the requirements defined for the parent element.

Property Set: Alignment General

ID Description Type Units Cardinality
alignment-id Unique identification of the alignment for reference for vertical alignment, corridor elements, and other roadside components. String   required
alignment-description Description of the alignment to further explain purpose and/or location. String   required

Requirements

  • All Horizontal Alignments must have the property Alignment ID in the set Alignment General.
  • All Horizontal Alignments must have the property Alignment Description in the set Alignment General.

Property Details

Alignment ID

Unique identification of the alignment for reference for vertical alignment, corridor elements, and other roadside components. Requirement: All Horizontal Alignments must have the property Alignment ID in the set Alignment General.

Alignment Description

Description of the alignment to further explain purpose and/or location. Requirement: All Horizontal Alignments must have the property Alignment Description in the set Alignment General.

Property Set: Direction of Travel

ID Description Type Units Cardinality
direction-of-travel The direction in which vehicles are moving on a roadway maybe expressed in terms of cardinal directions String   required

Requirements

  • All Horizontal Alignments must have the property Direction of Travel in the set Direction of Travel with a value being one of N, S, E, W, N/S, E/W.

Property Details

Direction of Travel

The direction in which vehicles are moving on a roadway maybe expressed in terms of cardinal directions Requirement: All Horizontal Alignments must have the property Direction of Travel in the set Direction of Travel with a value being one of N, S, E, W, N/S, E/W.

Property Set: Horizontal Alignment Designation

ID Description Type Units Cardinality
baseline Baselines are established as straight line segments or curves between known fixed points, generally within the right-of-way. Boolean   required
horizontal-control-line Control for horizontal alignment. The stationing for the roadway is measured along this line. Boolean   required

Requirements

  • All Horizontal Alignments must have the property Baseline in the set Horizontal Alignment Designation with a value being one of Yes, No.
  • All Horizontal Alignments must have the property Horizontal Control Line in the set Horizontal Alignment Designation with a value being one of Yes, No.

Property Details

Baseline

Baselines are established as straight line segments or curves between known fixed points, generally within the right-of-way. Reference: New York State Department of Transportation Highway Design Manual Requirement: All Horizontal Alignments must have the property Baseline in the set Horizontal Alignment Designation with a value being one of Yes, No.

Horizontal Control Line

Control for horizontal alignment. The stationing for the roadway is measured along this line. Reference: New York State Department of Transportation Highway Design Manual Requirement: All Horizontal Alignments must have the property Horizontal Control Line in the set Horizontal Alignment Designation with a value being one of Yes, No.

Property Set: Superelevation

ID Description Type Units Cardinality
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. Real Stationing required
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). Real Feet required
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. Real Stationing required
reverse-crown-station Refers to the point where the slope of a lane being rotated is the reverse of a normal crown. Real Stationing required
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. Real Feet required
full-superelevation-length Refers to the point where the roadway is sloped at the design superelevation rate E. Real Feet required

Requirements

  • All Horizontal Alignments must have the property End Normal Crown Station in the set Superelevation.
  • All Horizontal Alignments must have the property Tangent Runout Length in the set Superelevation.
  • All Horizontal Alignments must have the property Level Crown Station in the set Superelevation.
  • All Horizontal Alignments must have the property Reverse Crown Station in the set Superelevation.
  • All Horizontal Alignments must have the property Superelevation Runoff Length in the set Superelevation.
  • All Horizontal Alignments must have the property Full Superelevation Length in the set Superelevation.

Property Details

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. Synonyms: Tangent Runout Begin, Normal Slope Requirement: All Horizontal Alignments must have the property End Normal Crown Station in the set Superelevation.

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). Reference: Illinois Department of Transportation, Bureau of Design and Environment Manual, July 2024 Revision Requirement: All Horizontal Alignments must have the property Tangent Runout Length in the set Superelevation.

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. Synonyms: End Tangent Runout, Level Slope, No Crown Requirement: All Horizontal Alignments must have the property Level Crown Station in the set Superelevation.

Reverse Crown Station

Refers to the point where the slope of a lane being rotated is the reverse of a normal crown. Synonyms: Adverse Crown, Reverse Slope Requirement: All Horizontal Alignments must have the property Reverse Crown Station in the set Superelevation.

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. Reference: Illinois Department of Transportation, Bureau of Design and Environment Manual, July 2024 Revision Requirement: All Horizontal Alignments must have the property Superelevation Runoff Length in the set Superelevation.

Full Superelevation Length

Refers to the point where the roadway is sloped at the design superelevation rate E. Requirement: All Horizontal Alignments must have the property Full Superelevation Length in the set Superelevation.

Property Set: Alignment Coordinates

ID Description Type Units Cardinality
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. Real Feet required
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. Real Feet required
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. Real Feet required
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. Real Feet required

Requirements

  • All Horizontal Alignments must have the property Start of Alignment Coordinate - X in the set Alignment Coordinates.
  • All Horizontal Alignments must have the property Start of Alignment Coordinate - Y in the set Alignment Coordinates.
  • All Horizontal Alignments must have the property End of Alignment Coordinate - X in the set Alignment Coordinates.
  • All Horizontal Alignments must have the property End of Alignment Coordinate - Y in the set Alignment Coordinates.

Property Details

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. Requirement: All Horizontal Alignments must have the property Start of Alignment Coordinate - X in the set Alignment Coordinates.

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. Requirement: All Horizontal Alignments must have the property Start of Alignment Coordinate - Y in the set Alignment Coordinates.

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. Requirement: All Horizontal Alignments must have the property End of Alignment Coordinate - X in the set Alignment Coordinates.

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. Requirement: All Horizontal Alignments must have the property End of Alignment Coordinate - Y in the set Alignment Coordinates.

Property Set: Azimuth and Bearing

ID Description Type Units Cardinality
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. Real Degrees optional
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. Real Degrees optional
bearing-2 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. Real Degrees optional
azimuth-3 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. Real Degrees optional

Requirements

  • All Horizontal Alignment Curves may have the property Bearing in the set Azimuth and Bearing.
  • All Horizontal Alignment Curves may have the property Azimuth in the set Azimuth and Bearing.
  • All Horizontal Alignment Curves may have the property Bearing in the set Azimuth and Bearing.
  • All Horizontal Alignment Curves may have the property Azimuth in the set Azimuth and Bearing.

Property Details

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. Reference: Georgia DOT Basic Highway Plan Reading Requirement: All Horizontal Alignment Curves may have the property Bearing in the set Azimuth and Bearing.

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. Requirement: All Horizontal Alignment Curves may have the property Azimuth in the set Azimuth and Bearing.

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. Reference: Georgia DOT Basic Highway Plan Reading Requirement: All Horizontal Alignment Curves may have the property Bearing in the set Azimuth and Bearing.

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. Requirement: All Horizontal Alignment Curves may have the property Azimuth in the set Azimuth and Bearing.

Property Set: Horizontal Alignment Curve Length

ID Description Type Units Cardinality
length-of-circular-curve-lc 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. Real Feet required
length-of-spiral-ls 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. Real Feet required

Requirements

  • All Horizontal Alignment Curves must have the property Length of Circular Curve, Lc in the set Horizontal Alignment Curve Length.
  • All Horizontal Alignment Curves must have the property Length of Spiral, Ls in the set Horizontal Alignment Curve Length.

Property Details

Length of Circular Curve, Lc

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. Requirement: All Horizontal Alignment Curves must have the property Length of Circular Curve, Lc in the set Horizontal Alignment Curve Length.

Length of Spiral, Ls

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. Reference: New York State Department of Transportation Highway Design Manual Requirement: All Horizontal Alignment Curves must have the property Length of Spiral, Ls in the set Horizontal Alignment Curve Length.

Property Set: Horizontal Alignment Curve Type

ID Description Type Units Cardinality
circular An arc with a single constant radius connecting two tangents. Boolean   required
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. Boolean   required

Requirements

  • All Horizontal Alignment Curves must have the property Circular in the set Horizontal Alignment Curve Type with a value being one of Yes, No.
  • All Horizontal Alignment Curves must have the property Spiral in the set Horizontal Alignment Curve Type with a value being one of Yes, No.

Property Details

Circular

An arc with a single constant radius connecting two tangents. Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Curves must have the property Circular in the set Horizontal Alignment Curve Type with a value being one of Yes, No.

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. Reference: Illinois Department of Transportation, Bureau of Design and Environment Manual, July 2024 Revision Requirement: All Horizontal Alignment Curves must have the property Spiral in the set Horizontal Alignment Curve Type with a value being one of Yes, No.

Property Set: Circular Alignment

ID Description Type Units Cardinality
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. Real Degrees required
degree-of-curvature-d 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 Real Degrees / 100 ft required
  middle-ordinate-mo 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) Real Feet required    
  long-chord-lc �Long Chord” - Straight line distance from the P.C. to the P.T. REal Feet required
  external-distance-e Point of Intersection (PI) to mid-point of curve   Feet required
  radius A straight line distance from the center to the circumference of a circular curve. Real Feet required

Requirements

  • All Horizontal Alignment Curves must have the property Central Angle in the set Circular Alignment.
  • All Horizontal Alignment Curves must have the property Degree of Curvature (D) in the set Circular Alignment.
  • All Horizontal Alignment Curves must have the property Middle Ordinate (MO) in the set Circular Alignment.
  • All Horizontal Alignment Curves must have the property Long Chord (LC) in the set Circular Alignment.
  • All Horizontal Alignment Curves must have the property External Distance (E) in the set Circular Alignment.
  • All Horizontal Alignment Curves must have the property Radius in the set Circular Alignment.

Property Details

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. Requirement: All Horizontal Alignment Curves must have the property Central Angle in the set Circular Alignment.

Degree of Curvature (D)

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 Reference: WashDOT Highway Surveying Manual January 2005 Requirement: All Horizontal Alignment Curves must have the property Degree of Curvature (D) in the set Circular Alignment.

Middle Ordinate (MO)

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) Reference: Illinois Department of Transportation, Bureau of Design and Environment Manual, July 2024 Revision

Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Curves must have the property Middle Ordinate (MO) in the set Circular Alignment.

Long Chord (LC)

�Long Chord” - Straight line distance from the P.C. to the P.T. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Curves must have the property Long Chord (LC) in the set Circular Alignment.

External Distance (E)

Point of Intersection (PI) to mid-point of curve Reference: Illinois Department of Transportation, Bureau of Design and Environment Manual, July 2024 Revision Requirement: All Horizontal Alignment Curves must have the property External Distance (E) in the set Circular Alignment.

Radius

A straight line distance from the center to the circumference of a circular curve. Reference: TPF-5(480) SME Consensus Definition Requirement: All Horizontal Alignment Curves must have the property Radius in the set Circular Alignment.

Property Set: Spiral Alignment

ID Description Type Units Cardinality
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. Real Degrees required

Requirements

  • All Horizontal Alignment Curves must have the property Spiral Angle in the set Spiral Alignment.

Property Details

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. Requirement: All Horizontal Alignment Curves must have the property Spiral Angle in the set Spiral Alignment.

Property Set: Horizontal Alignment Curve Key Stations

ID Description Type Units Cardinality
curve-to-spiral-point-cs Point of change from circular curve to spiral Real Stationing optional
station-equation A point that relates a system of stationing to another system of stationing. Real Stationing optional
point-of-compound-curve-pcc Point common to two curves in the same direction with different radii Real Stationing optional
point-of-curvature-pc The point where a tangent ends and a curve begins. Real Stationing optional
point-of-intersection-pi The point where two tangents of a circular curve meet. Real Stationing optional
point-of-tangency-pt The point where a curve ends and straight alignment begins. Real Stationing optional
spiral-to-curve-point-sc 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 Real Stationing optional
spiral-to-tangent-point-st 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 Real Stationing optional
tangent-to-spiral-point-ts This is the point where the alignment changes from the back tangent to the entrance spiral Real Stationing optional
point-of-beginning-pob The point where an alignment begins. Real Stationing optional
point-of-ending-poe The point where an alignment ends. Real Stationing optional
point-on-curve-poc Point on a circular curve Real Stationing optional

Requirements

  • All Horizontal Alignment Curves may have the property Curve to Spiral Point (CS) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Station Equation in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Compound Curve (PCC) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Curvature (PC) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Intersection (PI) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Tangency (PT) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Spiral to Curve Point (SC) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Spiral to Tangent Point (ST) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Tangent to Spiral Point (TS) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Beginning (POB) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point of Ending (POE) in the set Horizontal Alignment Curve Key Stations.
  • All Horizontal Alignment Curves may have the property Point on Curve (POC) in the set Horizontal Alignment Curve Key Stations.

Property Details

Curve to Spiral Point (CS)

Point of change from circular curve to spiral Reference: WashDOT Highway Surveying Manual January 2005 Requirement: All Horizontal Alignment Curves may have the property Curve to Spiral Point (CS) in the set Horizontal Alignment Curve Key Stations.

Station Equation

A point that relates a system of stationing to another system of stationing. Synonyms: Equality Station, Station Relation Reference: Colorado DOT Basic Highway Plan Reading Course Requirement: All Horizontal Alignment Curves may have the property Station Equation in the set Horizontal Alignment Curve Key Stations.

Point of Compound Curve (PCC)

Point common to two curves in the same direction with different radii Reference: WashDOT Highway Surveying Manual January 2005 Requirement: All Horizontal Alignment Curves may have the property Point of Compound Curve (PCC) in the set Horizontal Alignment Curve Key Stations.

Point of Curvature (PC)

The point where a tangent ends and a curve begins. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Curves may have the property Point of Curvature (PC) in the set Horizontal Alignment Curve Key Stations.

Point of Intersection (PI)

The point where two tangents of a circular curve meet. Synonyms: HPI Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Curves may have the property Point of Intersection (PI) in the set Horizontal Alignment Curve Key Stations.

Point of Tangency (PT)

The point where a curve ends and straight alignment begins. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Curves may have the property Point of Tangency (PT) in the set Horizontal Alignment Curve Key Stations.

Spiral to Curve Point (SC)

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 Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Curves may have the property Spiral to Curve Point (SC) in the set Horizontal Alignment Curve Key Stations.

Spiral to Tangent Point (ST)

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 Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Curves may have the property Spiral to Tangent Point (ST) in the set Horizontal Alignment Curve Key Stations.

Tangent to Spiral Point (TS)

This is the point where the alignment changes from the back tangent to the entrance spiral Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Curves may have the property Tangent to Spiral Point (TS) in the set Horizontal Alignment Curve Key Stations.

Point of Beginning (POB)

The point where an alignment begins. Reference: Bridge Geometry Manual

Publication No. FHWA-HIF-22-034 Requirement: All Horizontal Alignment Curves may have the property Point of Beginning (POB) in the set Horizontal Alignment Curve Key Stations.

Point of Ending (POE)

The point where an alignment ends. Requirement: All Horizontal Alignment Curves may have the property Point of Ending (POE) in the set Horizontal Alignment Curve Key Stations.

Point on Curve (POC)

Point on a circular curve Requirement: All Horizontal Alignment Curves may have the property Point on Curve (POC) in the set Horizontal Alignment Curve Key Stations.

Property Set: Horizontal Alignment Tangent Length

ID Description Type Units Cardinality
tangent-length Length of straight segments of alignment Real Feet required

Requirements

  • All Horizontal Alignment Tangents must have the property Tangent Length in the set Horizontal Alignment Tangent Length.

Property Details

Tangent Length

Length of straight segments of alignment Reference: New York State Department of Transportation Highway Design Manual Requirement: All Horizontal Alignment Tangents must have the property Tangent Length in the set Horizontal Alignment Tangent Length.

Property Set: Horizontal Alignment Tangent Key Stations

ID Description Type Units Cardinality
station-equation A point that relates a system of stationing to another system of stationing. Real Stationing optional
point-of-curvature-pc The point where a tangent ends and a curve begins. Real Stationing optional
point-of-intersection-pi The point where two tangents of a circular curve meet. Real Stationing optional
point-of-tangency-pt The point where a curve ends and straight alignment begins. Real Stationing optional
spiral-to-tangent-point-st 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 Real Stationing optional
tangent-to-spiral-point-ts This is the point where the alignment changes from the back tangent to the entrance spiral Real Stationing optional
point-of-beginning-pob The point where an alignment begins. Real Stationing optional
point-of-ending-poe The point where an alignment ends. Real Stationing optional
point-on-tangent-pot A point on the tangent line that is used in the projection of the tangent line in a forward direction. Real Stationing optional

Requirements

  • All Horizontal Alignment Tangents may have the property Station Equation in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point of Curvature (PC) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point of Intersection (PI) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point of Tangency (PT) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Spiral to Tangent Point (ST) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Tangent to Spiral Point (TS) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point of Beginning (POB) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point of Ending (POE) in the set Horizontal Alignment Tangent Key Stations.
  • All Horizontal Alignment Tangents may have the property Point on Tangent (POT) in the set Horizontal Alignment Tangent Key Stations.

Property Details

Station Equation

A point that relates a system of stationing to another system of stationing. Synonyms: Equality Station, Station Relation Reference: Colorado DOT Basic Highway Plan Reading Course Requirement: All Horizontal Alignment Tangents may have the property Station Equation in the set Horizontal Alignment Tangent Key Stations.

Point of Curvature (PC)

The point where a tangent ends and a curve begins. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Tangents may have the property Point of Curvature (PC) in the set Horizontal Alignment Tangent Key Stations.

Point of Intersection (PI)

The point where two tangents of a circular curve meet. Synonyms: HPI Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Tangents may have the property Point of Intersection (PI) in the set Horizontal Alignment Tangent Key Stations.

Point of Tangency (PT)

The point where a curve ends and straight alignment begins. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Tangents may have the property Point of Tangency (PT) in the set Horizontal Alignment Tangent Key Stations.

Spiral to Tangent Point (ST)

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 Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Tangents may have the property Spiral to Tangent Point (ST) in the set Horizontal Alignment Tangent Key Stations.

Tangent to Spiral Point (TS)

This is the point where the alignment changes from the back tangent to the entrance spiral Reference: Wyoming Department of Transportation

Road Design Manual Requirement: All Horizontal Alignment Tangents may have the property Tangent to Spiral Point (TS) in the set Horizontal Alignment Tangent Key Stations.

Point of Beginning (POB)

The point where an alignment begins. Reference: Bridge Geometry Manual

Publication No. FHWA-HIF-22-034 Requirement: All Horizontal Alignment Tangents may have the property Point of Beginning (POB) in the set Horizontal Alignment Tangent Key Stations.

Point of Ending (POE)

The point where an alignment ends. Requirement: All Horizontal Alignment Tangents may have the property Point of Ending (POE) in the set Horizontal Alignment Tangent Key Stations.

Point on Tangent (POT)

A point on the tangent line that is used in the projection of the tangent line in a forward direction. Reference: Illinois Department of Transportation, Survey Manual, May 2015 Revision Requirement: All Horizontal Alignment Tangents may have the property Point on Tangent (POT) in the set Horizontal Alignment Tangent Key Stations.