One of the cool features of Civil 3D 2012 is the ability to force tangency on an alignment. This can occur if you are starting an alignment from lines/polylines and the sections are not quite tangent with each other.
When you create the alignment from these entities, by default a warning symbol will appear over the section where it is not tangent with the other entity.
This can be turned on or off from the Alignment Properties found on the Alignment tab and Modify panel. Or you can simply right-click on the alignment and select Alignment Properties. The Alignment Properties dialog will open. It is the Design Criteria tab that you are interested in.
When you take a look at the alignment, a little more in-depth by looking at the Geometry Editor (Alignment tab, Modify panel) and then selecting the Alignment Grid View tool, you can see the alignment tangency problems a little clearer.
By clicking on one of the Tangency Constraints that are highlighted as not being tangent, you can see some new options.
For the purposes of our exercise, we want to make the lines/curves all tangent to each other. So we will select the Constrained on Both Sides (Free) option.
You can see instantly, that the arc section has been modified so that tangency is created. The warning symbol disappears. Do this for all constraints which are not constrained. Further, you can (of course) modify the curve radius for each curve section.
So, you can see the finished alignment. The new alignment tools in Civil 3D 2012 are indeed powerful.