In AutoCAD Civil 3D, using the intersection command can yield disappointing results under certain conditions. One of them is when an incoming road is wider than its outgoing version.
In the intersection offset parameters dialog, there is no accounting for the offset value of the incoming or outgoing geometry of the road, just the left and right side.
In this case, it is not necessary to abandon the intersection command to manually create this area of the corridor. With a few grip edits after the creation of the intersection, we can still make the intersection work for us.
In this scenario, create the intersection by entering the widened version of the primary road for the left and right offset values. No out-of-the-ordinary adjustments need to be made to the other intersection parameters.
Once the intersection is created, temporarily turn off the corridor layer.
Drag the intersection label out of the way and note the left and right offset alignments for the primary road which is the widened road in this case.
Click on one of the offset alignments for the primary road, then click the grip that looks like a plus sign to create a widening.
Click the triangular grip to adjust the widening so it coincides with the width of the outgoing part of the primary road. You will see the curb return alignment automatically adjust.
Click the large round grip to activate/reveal the widening grips. These will appear as two smaller round grips to each side of the larger one.
Take each widening grip (the smaller round grips and pull up to coincide with the curb return of the incoming road and the curb return of the outgoing road.
Repeat for the other side.
Rebuild the corridor and turn on the corridor layer. Rebuild the intersection if necessary.
Using this method of inserting widenings on the primary road’s offset alignments, keeps the intersection in a state where the parametric relationships created by the intersection command remain dynamic with any design changes that may occur later in the intersecting roads.
– Cyndy Davenport