Creating NURBS Roadways

The Roadway (NURBS) tool uses NURBS curves to define the road shape. However, the Roadway (NURBS) object does not represent accurate alignments of low-speed roadways, which are typically constructed with arcs (constant radius) and tangents (straight lines); use the Roadway (Poly) tool for this.

NURBS roadways can also be created by drawing a polyline or polygon and then selecting the Create Objects from Shapes command (see Creating Objects from Shapes).

● Select Redistribute and Smooth Curve from the Object Info palette of the selected roadway once or twice to smooth out the road slightly, so it does not follow every hill and valley in the existing terrain.

● Manually reshape the road in 3D as required (to match other road elevations, garage elevations, and so on).

● Only select Redistribute Stations for more or fewer station annotations. Fewer stations are easier to work with when sketching and reshaping, but a road construction company might require more stations to be specified. Redistribute Stations is also useful to ensure that the station spacing is equal after reshaping the road.

2. Click in the drawing file to set the start point of the road, and then click to set the position of each additional NURBS vertex. Double-click the last point to complete creation of the roadway (NURBS) object.

3. If this is the first time a NURBS roadway is placed on the drawing, the object properties dialog box opens. Specify the default preferences, which apply to all NURBS roadways placed subsequently in this drawing. Click OK.

Parameter	Description
Z height	Adjusts the elevation of the entire road
Rotation	Specifies the number of degrees to rotate the object (0.00 is horizontal)
Text Style	Select a text style from either the default content or the current file’s content. To use the style associated with the class, select <Class Text Style>. To format the text using options on the Text menu, select <Un-Styled>. See Using Text Styles and Formatting Text.
Road Length	Displays the length of the road
Paving Width	Specifies the overall width of the paved road surface (without curbs)
Paving Height	Specifies the road paving thickness (without curbs)
Curb Width	Specifies the curb or shoulder width
Curb Height	Specifies the curb or shoulder height
Left Guardrail	Adds a guardrail to the left side of the road
Right Guardrail	Adds a guardrail to the right side of the road
Show Stations	The NURBS curve vertices are used as the station points; select to display the station points. In 2D, stations display as loci with text displaying the point elevation. In 3D, the stations display as round stakes.
Create Pad for Site Model	Creates a pad modifier for the Roadway (NURBS) object
Create Grade Limits for Site Model	Creates a grade limits modifier for the Roadway (NURBS) object, to control the zone where the terrain transitions between the existing elevation and the road elevation
Grade Limits Method	Specify whether to create offset or sloped grade limits
Grade Limits Off.	When creating offset grade limits, specify the distance from the road to the grade limits
Grade Limits Slope	When creating sloped grade limits, specify the batter slope
Paving/Curb Class	Select a class for each category of roadway geometry, to control the appearance and/or visibility. The classes present in the drawing are listed; alternatively, create a new class by selecting New, select the default class name (roadway items are placed in the Site-Paving class category), or select the Roadway (NURBS) class, which places the paving item in the same class as the NURBS roadway object.
Redistribute Stations	Redistributes the stations at a specified spacing interval
Redistribute and Smooth Curve	Redistributes the station points at a specified spacing interval and smooths the NURBS curve
Send Stations to Surface	Click to set the Z value of the stations to the surface of the site model. The stations can be set to either the surface of the existing site model, or to the surface of the proposed site model, which may have been altered by modifiers. If the stations are sent to the surface of a proposed site model which has been changed by modifiers, it may be necessary to deselect Create Pad for Site Model and Create Grade Limits for Site Model for the Roadway (NURBS) in order to prevent site modifier errors caused by crossing pads or grade limits.
Align Stations Vertically	Sets the elevation of the indicated station points to a specific plane. As the starting and ending stations are indicated, a red line previews the included station points. The % Grade indicates the grade that will be set between station points.
NURBS curve parameters	Edits the roadway NURBS curve

5. If necessary, use the Reshape tool to modify the locations of the vertices after object creation, or use the vertex editing controls on the Object Info palette to move the vertices or change the degree of vertices.

6. Update the site model. Select the site model and click Update from the Object Info palette.

Creating NURBS Roadways

Parameter

Description