Fixing bad triangles at intersections with null regions

Last updated: 2026-01-06

Total video time: 05:20

crdr-isu-null-regn.mp4 5:20

At some intersections, the corridor surfaces may exhibit undesirable triangulation within the curb return regions.

Due to unknown reasons, at times the surface triangles try to connect from a sideroad region on one side of the mainline to a sideroad region on the other side of the mainline. There are is a simple solution to break these connections.

Remove redundant feature lines

If not completed yet, adjust the intersection assemblies to remove redundant feature lines as shown here: Redundant intersection corridor feature lines (wi.gov). This should be done on every intersection on every project.

Add a null region on the sideroad baseline

If removing redundant feature lines does not correct this situation, add in a null region along the sideroad baseline. When building an intersection, a designer may typically only have corridor regions on the sideroad where there is a roadway section that needs be built. Because part of the sideroad alignment/baseline goes through and intersects with the mainline corridor regions, there will be a gap in the regions along the sideroad baseline.

  1. Create a Null Assembly
    1. Home Tab > Create Design Panel > Assembly > Create Assembly
      1. Name: Null
      2. OK
    2. Digitize the location of the assembly
    3. Do not add any subassemblies. As the name implies, this assembly will be “empty.”
  2. Add a region in the sideroad gap using the Null assembly.
    1. Select the corridor > Contextual Ribbon > Add regions
    2. Select the sideroad baseline
      1. Utilize the baseline preview to determine and select the sideroad baseline.
    3. Specify the region start station
      1. The region should begin at the intersection of the sideroad alignment and mainline ETW.
    4. Specify the region end station
      1. The region should end at the intersection of the sideroad alignment and opposite mainline ETW.

    5. Create Corridor Region dialog:
      1. Region Name: Leave default or assign custom region name
      2. Assembly: Null
      3. OK
    6. Warning Dialog box: No targets found in scripts
      1. OK
  3. Verify that triangulation is corrected.