Technically, the answer to the question above is “when it has a zero radius.” In other words, a curve isn’t a curve when it’s a line – or is it?
I’ll be the first to admit that I don’t know everything (shocking, isn’t it?) And, I have plenty of friends who seem to wait for me to be wrong so they can gleefully point it out and laugh at me. So I won’t say it was a terrible shock last night when I was watching House, MD and my phone buzzed. It was one of my closest friends, Nick Zeeben, pointing out that I was wrong, wrong, wrong. You see, he had read the comments on this post of mine and noticed that I was incorrectly saying that you cannot add superelevation to an alignment with no curves. Nick schooled me and showed me that it could be done, and knowing what a hot topic this is, I wanted to share with you, Loyal Reader (nothing like a 7:30 AM reference to Stephen King, huh?) So without further ado, I’d like for you to hit the jump so that I can school you just as I was schooled last night.
Above, you see an alignment. Look at all those curves! No? Well, for the sake of this blog post, we’re going to imagine curves in this alignment – or at least one curve. And we’re not only going to imagine it, we’re going to superelevate it. So let’s get started!
First, I am going to select the alignment. I do this simply because it brings up the contextual ribbon and allows me to see the alignment-specific commands. I want to pick the Superelevation pulldown on the Modify panel and select Calculate/Edit Superelevation, as shown below:
Once the Calculate/Edit Superelevation button is selected, a new dialog will pop up with two options – you can either calculate the superelevation now or open the superelevation curve manager. This is where the program starts to eat at your logical brain – or at least mine. I would expect to calculate superelevation, right? After all, there are no curves in my alignment, so why would we need to go into the superelevation curve manager? All I have to say here is don’t trust your brain – you’re going to need to click on Open the Superelevation Curve Manager. I know it defies all logic, but just do it.
Now you should be seeing the Superelevation Curve Manager palette, as shown below:
You should notice a not-too-surprising lack of data here – we don’t have any curves, so why should there be curve information displayed here? To add in information, there is a handy button that says Create User Defined Curve. Going back to the title of this post, remember that a curve doesn’t always have to be a curve, at least not in this scenario. Click the button and see what happens. The command line will say “Select starting entity for superelevation curve group.” If you’ve read this far, you can probably guess what I’m about to do and you will probably think I’m crazy. Well I am, just a little, but humor me anyway – pick the beginning of the alignment (which is simply a single tangent.) Now you will be asked to select the ending entity for superelevation curve group. I picked toward the end of the tangent, and the whole tangent lit up, as shown below:
What’s more, you will now see some data in the Superelevation Curve Manager – granted, it’s not calculated yet, but it gives you something to calculate:
Now, change anything in here that you might need to change, such as the design speed, and then you can calculate your superelevation via the superelevation wizard. If you’re not familiar with the wizard, then you probably are really confused by this point. If you are, go through it and work your magic. Once you are finished, let the program know by clicking the Finish button on the wizard.
Once that window is closed, you have a panorama showing that gives you all of your superelevation data, as shown below:
Here, you can tweak and edit your superelevation to your heart’s delight.
I hope this clears things up a bit regarding superelevation on tangents. Much thanks to Nick Zeeben, AutoCAD Civil 3D Product Manager for setting me straight so I can bring the news to you. You’ll be hearing a bit more about Nick in the near future – stay tuned!