Horizontal Alignment Options

Use the first set of these options to define each horizontal segment in a horizontal alignment (HAL). Use the second set of options to define each curve at a Point of Intersection (PI) in a HAL. They are available on the Horizontal tab of the Alignment Editor.

Note: The input modes are defined in Project Settings, which can be accessed by clicking the Project Settings icon in the editor.
Note: Depending on the input mode that is set, some of the values below may not be required.


Segment-based alignment options
Type	POB (Point of Beginning) - Denotes the starting point for the alignment. Define the station, and northing and easting coordinates of the POB. Line - Select this to enter a straight segment. Define the azimuth or bearing, and length of the line. Note: Segment transitions default to tangent. Arc - Select this to enter a curved segment with a constant radius. Define the azimuth or bearing, radius, direction of the curve, and length/delta/station (depending on the input mode defined in Project Settings). Spiral In - Select this to enter a transitional spiral segment with a decreasing radius. Generally, use this to connect a line with an arc. Define the azimuth or bearing, radius, direction of the curve, and length/station/A parameter. Spiral Out - Select this to enter a transitional spiral segment with an increasing radius. Generally, use this to connect an arc with a line. Define the azimuth or bearing, radius, direction of the curve, and length/station or A parameter. Combining Spiral - Select this to spiral between two arcs with different radii. Define the azimuth or bearing, side from the POB, radius 1, radius 2, and length/station/A parameter. Note: See also the Spiral Type and Curve Type Combinations section in Create anAlignment.
Azimuth (North or South) or Bearing	Specify a bearing or an azimuth value at the beginning of the segment, or accept the default of Tangent, which is the bearing from the previous segment. For lines, this is the bearing of the entire segment. For arcs and spirals, it is the tangent bearing into the segment.
Radius	Specify the distance between the arc and its center point.
Left / Right	Select the direction an arc should curve (left or right) in the direction from the POB.
Length	Specify the length of the segment. For arcs, and spirals, this is the actual length, not a chord length.
Delta	Specify the central angle of the arc.
A Param	Specify the standard factor used as a roadway design criteria in establishing the required length of the spiral. The A parameter reflects the rate of change of the radius, in relation to the distance along the spiral.
Station	Specify the station value at the end of the POB segment. For other segment types, this either displays the computed station or requires a station to be entered, depending on the input mode. To base alignment stationing on a different alignment: Use reference alignment stationing to apply stationing based on the stationing of another alignment (usually where a design alignment is slightly different from the as-built alignment). Select the main alignment and press [F11] to open the Properties pane. Find the Appearance section and select the reference alignment that has the stationing you want to use in the Reference Alignment list. Note: The stationing shown in the Alignment Editor does not change when based on a reference alignment. Tip: You can confirm the use of a reference alignment's stationing by selecting the main alignment, right-clicking in any Coordinate control (such as used, e.g., in Pan Precise), selecting Offset > Offset Line snap, picking the main alignment, and moving your cursor along the main alignment. The rubber-band line will be perpendicular to the alignment based on the stationing of the reference line, not its own stationing. In this simplified example, notice how the rubberband line is perpendicular to the lower reference alignment, not the main alignment above it.
Northing	Specify the northing coordinate of the POB. For other segment types, this displays the computed northing coordinate of the segment's end point. Note: The order of the Northing and Easting columns can be set in Project Settings by clicking the Project Settings icon.
Easting	Specify the easting coordinate of the POB. For other segment types, this displays the computed easting coordinate of the segment's end point.
PI-based alignment options
Type	No curve - Select this to create a straight segment at the PI. Typically, this is used for transitions with a small delta. Define the northing and easting coordinates of the PI. Arc - Select this to inscribe an arc with a constant radius from the Point of Curvature (PC) to the Point of Tangency (PT). Define the radius of the arc, and the northing and easting coordinates of the PI. Spiral - Select this to inscribe a curve that spirals in from the PC for a defined distance, then arcs, and then spirals out for a defined distance to the PT. Define the radius, spiral in distance, spiral out distance, and the northing and easting coordinates of the PI.
Radius	Specify the distance between the arc and its center point.
Spiral In	For the start of spiral curves, specify the length of the transitional spiral with a decreasing radius.
Spiral Out	For the end of spiral curves, specify the length of the transitional spiral with an increasing radius.
Station	Specify the station value of the POB.
Northing	Specify the northing coordinate of the POB or PI.
Easting	Specify the easting coordinate of the POB or PI.