Create Curves at Horizontal Intersection Points

Description

Create combined curves at an alignments horizontal intersection points using a horizontal design standard and a design velocity.

Access

Alignment / Properties / Horizontal Intersection Points Intersection Points

Requirements

Design module
A horizontal design standard

Controls

Control	Description
Alignment	Select an alignment to compute curves at horizontal intersection points.
Horizontal Standard	Select the horizontal design standard to use for the curve computations.
Alignment Velocity	Type the design velocity for the alignment. Note: If you edit the alignment velocity all curves computed using the Alignment Velocity method are recomputed.

List Controls	Description
Automatic	Do one of the following: Select the checkbox to recompute the curve and allow the Curve Type to change when the curves are recomputed due to changes in the alignment geometry or the Horizontal Standard. Clear the checkbox to preserve the curve type when the curves are recomputed. Note: If you edit the Curve Type, the checkbox is automatically cleared. If you change to a different design standard the checkbox is automatically selected.
Intersection Point	All horizontal intersection points in the alignment. Note: A vertex between two straight segments in an alignment is considered an intersection point. An attempt is made to fit a curve that complies the standard at these vertices.
Curve Type	An attempt will be made to compute a curve within the horizontal design standard constraints at each intersection point. You can override the computed curve type. No Curve - A curve is not placed at the intersection point Circular Curve - A circular curve is placed at the intersection point Combined Curve - A circular curve and two equal transitions are places at the intersection point. Note: To comply with the standards, curves must be separated by straights using the minimum curve separation value defined in the horizontal design standard. A curve type highlighted red indicates the curve could not be computed but there were no design parameter failures. Check that the curve geometry can be created with the curve separation requirement specified in the standard. A curve type highlighted amber indicates the curve could be computed but the curve type is different to what is required by the design standard. This will only occur if you override the curve type that is automatically generated.
Method	The method used to compute curve: Alignment Velocity - A minimum radius is computed for the curve using the Alignment Velocity, the side friction coefficient determined from the maximum side friction parameter set and the superelevation determined from the maximum superelevation parameter set. If the computed radius is less than the maximum radius requiring transition curves, transition lengths are then applied using the minimum transition length for the Alignment Velocity. If the curve computation method in the horizontal design standard is configured to 'Design Minimum' the curve is created at the smallest allowable radius taking into account the minimum curve length. If the curve computation method in the horizontal design standard is configured to 'Design Maximum' the curve is created at the largest possible radius taking into account the minimum curve length, minimum transition length and the curve separation. Velocity - Type a velocity in the Velocity column. A minimum radius is computed for the curve using the velocity, the side friction coefficient determined from the maximum side friction parameter set and the superelevation determined from the maximum superelevation parameter set. If the computed radius is less than the maximum radius requiring transition curves, transition lengths are then applied using the minimum transition length for the keyed in Velocity. If the curve computation method in the horizontal design standard is configured to 'Design Minimum' the curve is created at the smallest allowable radius taking into account the minimum curve length. If the curve computation method in the horizontal design standard is configured to 'Design Maximum' the curve is created at the largest possible radius taking into account the minimum curve length, minimum transition length and the curve separation. Radius - Type a radius in the Radius column and a velocity in the Velocity column. The curve length is computed using the keyed in Radius. If the radius is less than the maximum radius requiring transition curves, transition lengths are then applied using the minimum transition length for an internally computed velocity, suitable for the keyed in Radius. Transition Length - Type a radius in the Radius column, a transition length in the Transition Length column and a velocity in the Velocity column. The transition length is held fixed and the radius is used to compute the velocity allowed using the design standards. Curve Length - Type a curve length in the Curve Length column and a velocity in the Velocity column. Note: If the method on existing curves is something other than 'Design Velocity' the keyed in value will be preserved when updating the alignment.
Velocity	The design velocity for the curve. Note: This is the Alignment Velocity when the Method is configured to 'Alignment Velocity'. You can key in a value when the Method is configured to something other than 'Alignment Velocity'.
Radius	The curves radius. Note: When the Method is configured to 'Alignment Velocity' and the Curve Computation method in the horizontal design standards is configured to 'Design Minimum' this value is the minimum radius computed for the curve. You can key in a value when the Method is configured to 'Radius'. The keyed in value is highlighted amber if it is less than the minimum radius computed for the curve at the design Velocity.
Length	The length of the curve. Note: When the Curve Type is 'Combined Curve' this is the total length of the circular curve and the two transition curves. A curve length highlighted amber, indicates that the curve length is less than the minimum curve length for the velocity. You can key in a value when the Method is configured to 'Curve Length'.
Transition Length	The length of the transition curve. Note: If the computed transition curve is highlighted amber, the transition length is less than the minimum transition curve length configured for the design velocity. You can key in a value when the Method is configured to 'Transition Length'.

Notes

Select an alignment in the model view prior to clicking the command to automatically select the Alignment.
The curves are automatically computed when you select a design standard.
Select the 'Alignment Velocity' or 'Velocity' method to compute the best values for the curves based on the design standard. Select alternate methods if you want to input and fix a preferred value for a curve component.
Click outside the control to compute the curve using the Method, the keyed in values and the horizontal design standard.
Click OK to accept the curve geometry for all alignments. If a curve was unable to be computed at an intersection point, a curve will not be generated at this location in the alignment geometry.
Click Cancel revert to the original alignment geometry.
When a horizontal standard is applied to an alignment the alignment will always start and end with straight.
The computed entry and exit transitions are equal length.
If the selected alignment has pre-existing curves and the horizontal design standard has not changed, the curve type, method and previously fixed values will be retained.
If the design standard is changed to another standard, the method and previously fixed values will be retained, however the curve type may change depending on the design parameters.
If the design standard is changed to 'None', no curves will be displayed for the intersection point. Click OK to save the alignments geometry but disconnect it from the design standard.
If the design standard is changed from 'None' to a project horizontal standard, the curve computation determines a suitable design velocity for the radius of the curve at the intersection point, then uses the Radius curve computation method to compute a curve that complies with the design standard while attempting to maintain the appearance of the alignment. If an alignment contains a transition curve the transition curve method is used to preserve the length of the transition curve. You should choose a design standard that replicates the standard initially used to design the alignment. If the entry and exit transition curves at an intersection point are a different length, only one of the transition lengths is preserved.
If a curve cannot be computed for the intersection point, within the constraints of the horizontal design standard, the curves row is highlighted red. A cell highlighted amber in this row, indicates the value does not satisfy the parameters. You should, review the placement of the intersection points, the design velocity, the horizontal design standard, and the method and curve type used to compute the curve.
Curves will not be generated at the start and end vertices of the alignment.

Possible Errors

Error message	Description	Solution
Could not compute the curve with the current design parameters.	A curve could not be computed using the design parameters and design standards configured for the alignment.	Try one of the following: Consider lowering the design velocity for the curve. Change the alignment geometry so that it is better suited to the specified design standards.