How do I build a highway interchange (curves, grades, etc) and is SketchUp right for my intentions?


Hi all…

Humbly, I have two questions.

I’m coming to SketchUp endeavoring to better my drawing and painting skills. I want to use the program to aide with perspective when composing pictures or shots. I love being able to move around a space to find a frame. For this, I also appreciate the camera tools. I’d like SketchUp to help me with lighting as well, or at least shadows and how they fall on forms. The idea is then to take these basic constructions from SketchUp as 2D images and work on them in a painting program.

For example, I would like to build a highway interchange, with ramps and curved roadways. I first searched the older Google groups before finding the forums here, and it appears this objective came up a few times over the years. The most recent I found was from 2010. Help from the community usually involved recommending multiple plug-ins along with (what seemed to me like) tedious work. I was/am intimidated, and so before digging into those old instructions, figured I’d see if things have changed at all toward that kind of thing being any easier or more novice-friendly.

Have there been additions to the software or plug-ins since then that facilitate in this? I used SketchUp 8 for a while a few years ago. I’ve just downloaded the 2015 Pro trial.

I love SketchUp, and look forward to learning more of the program. But my skill level is rudimentary. And so my other question is, before I leave the trial version and somehow cobble together enough to buy the real deal (I think I need Pro because of the camera tools), does anyone think I’d be better off using something else for the purposes described. Thanks for your time and mind.



I don’t know how accurately you are wanting to model the grades and roadways, but if you’re just looking for a way to quickly lay things out and then followup with using it as a template for a final drawing, the Spirix plugin might be of interest. Since roads are simply a cross-section driven perpendicularly to the direction of travel, Spirix can pretty much create any combination of extruded spiraling rotating helical surfaces to describe them.

Here’s a whimsical animation of a “roadway” created using Spirix:


Here’s an overpass I modeled using native tools for a similar question:



(cracking knuckles)

Thanks jimhami42 and Gully! When I can do similarly to either of your examples I will be very pleased.




I have the spirix added to my extensions: alas I am very unable to make use of it to design a road. Could kindly you specify the process…for this looks to be the exact and ideal way to create overpasses, road lengths, ect.

Many Thanks,


I feel your pain. It’s not a very easy-to-use plugin and the documentation is sketchy. Much of what it can do is better handled by other plugins or simply using the built-in functions of SketchUp. However, it does have a couple of functions that allow you to create polygon mesh surfaces that combine simultaneous mathematical transformations. Also, make sure you have the newest version [here] as it works in metric as well.

The best approach is to create a sequence* of edges and circles and then use the Spirix Group function to name them for future reference. The group is then used as a generatrix for the desired surface(s).

(1) Groups may be revolved about the z-axis any number of times (1.0 rev = 360 degrees) creating a specified number of segments comprising the contour… any contours should be oriented in the +X/Z plane in reference to the origin**. While being revolved, a group may also simultaneously change in Z (helix) and/or X (spiral) and/or rotate about an arbitrary centroid offset in X and Y and/or morph into another group’s shape and/or be scaled (down to 0.0 is okay). Each of the sub-transforms are performed using a variety of math functions that specify the equations used to describe the desired path.

(2) If not revolved about the z-axis, the groups should lie in the X/Y plane. In this mode, a group can be rotated about its centroid (or offsets) while being shifted in X and/or scaled and/or changing in Z (height) and/or morphing into another group.

(3) Offset surfaces can be created to add a uniform arbitrary thickness to a surface (as well as side and end “skirts” to make it solid).

I think it can help in some parts of it … it’s intended to add some more polygon mesh creation tools to your toolbox.

*sequence of edges - geometry must be created in the order you want the points to be processed. When grouping the geometry using the Spirix Group function, there should be no other “loose” (or un-grouped) geometry except what you want for your contour. Creating the contours and naming them is a good place to start. Once grouped, they can be scaled, moved, rotated, etc. for use.

Here’s a simple example … a 12m lane width to 8m transition while rising (or falling) 10m and merging 12.72m sideways. I created a 12m line and used the Spirix Group funtion to name it “L1” and then created a second 8m line and named it “L2”. Then I moved things around in the X/Y plane and used the Spirix Surface function with the parameters shown to create the surface. I then moved it into place and added lane extensions:

If you can provide some sort of idea of what you need, I’ll be happy to try and help you with specifics. With more specifics, you might also get additional assistance from others to do what you need in a simpler way or using another plugin.