Design Horizontal Alignment
The function then prompts you to select the design segment you wish to you. After doing so, it will show the design horizontal alignment form, and number each inflection point on the design segment.
To run this function: Choose Design > Road design > Design horizontal alignment, or...
Fields on the Design horizontal alignment form
Design Segment
Output string: The string that is created by this function. A new segment containing the curved horizontal design will be created at the end of this string.
Name: The name of the road. This has no effect on the road design at all, but the road name is placed in D1 on the first point of both the design segment, and the output segment.
Initial Chainage: This will be the chainage value of the very first point produced. All chainage values appear in D2 during the road design process.
Chainage Interval: This is the distance between each point produced for the curved road centreline.
Calculate Road Parameters
This is used to aid the you in calculating transition curve lengths and super elevations for the road. You type in the speed of the vehicles, and then hit the calculate button. Any row in the road design details section that does not have the "Fixed" column ticked will have the transition length and super elevation values changed to match the vehicle velocity. Note that this may produce an invalid road design, and the status of those rows and the surrounding rows will be set to "Invalid".
Road design details
This section allows you to edit the specific details for the road design. For each inflection point you can manipulate the radius of curvature, transition length and superelevation.
The radius for each inflection point is the radius used to create the circular curve to go between straight road segments. The curve will be placed so that the incoming and outgoing tangents of the circle match that of the straight road segment.
The transition length row allows you to add in a transition curve on both sides of the circular curve. This gives a smoother curve into the circular curve. The length of measurement here is the length along the road curve.
The superelevation is the amount of tilt applied to the road. The angle here must always be greater than or equal to zero, because the road will always tilt inwards if it needs to.
Output
After filling out the form, press apply, and a new segment will be created in the specified string that contains the new curved road centreline. Each point on the new centreline will have the following information in the description fields
D2 - chainage of the point. This is how far along the road curve a point is
D3 - This contains either "Circular Curve", "Tangent Point", or is empty. Any point marked with "Tangent Point" indicates this is the point where a straight segment of road becomes a curve. The curved part may either be a transition curve, or a circular curve depending on what was used. If a point has "Circular Curve" in D3, then this point marks where a transition curve transforms into a circular curve.
D4 - Contains the superelevation at the given point, or it can be empty. A point will only contains a superelevation value if it needs to, otherwise superelevations will be interpolated from the nearest known superelevations.