Corridor and refinement surface progression

Last updated: 2020-10-26

Recommended surface progression

There are multiple methods for creating the Datum and Top refinement surfaces. Both surfaces need to cover the entire limits of proposed work within Daylight codes (slope intercepts). To minimize the amount of data, work, and processing time, designers can create the Crdr-Top surface from Daylight to Daylight and create the Crdr-Datum surface only under the roadway, then paste it over the Rfnt-Top surface.

In the recommended progression, the Crdr-Datum surface only extends to the edge of the roadway subgrade (typically 2 ft outside the back of curb and gutter in urban or the subgrade shoulder point in rural). The Crdr-Top surface extends to the slope intercepts. Any refinements outside the roadway then automatically appear in the Rfnt-Datum surface.

Benefits

There are several instances in our roadway design workflows that require us to build an additional surface in order to progress the design. Listed below are a few of those cases:

  1. Pipe Networks: For pipe networks, we create a special corridor surface called Crdr-PipeDatum. The purpose of this surface is to provide a reference for the pipe network cover rule. This surface includes the roadway subgrade only. Since the recommended Crdr-Datum surface has the same definition, the Crdr-PipeDatum surface can be eliminated.
  2. Crdr-Ultimate surface: This surface is used for several purposes and is typically combined with the existing surface to show a "finished project" state. Possible uses include rural driveway workflow, curb ramp workflow, visualization, and others. Since the recommended Crdr-Top surface has the same definition, the Crdr-Ultimate surface can be eliminated.
  3. Urban surface refinement: The benefit demonstrated is for surface refinements that span the ETW_Datum_CG feature line (point typically 2 ft behind curb and gutter). The purpose of those refinements is for driveways and curb ramps. The refinements must occur on a top surface that spans the ETW_Datum_CG feature line. Those refinements are then reflected automatically in the Rfnt-Datum surface. This recommended workflow can be beneficial anywhere there is a need for surface refinements that span the connection of Top and Datum.
  4. Quicker visualization models: If a quick visualization model is needed, the recommended Crdr-Top surface can be used.

Drawbacks

The drawback to this workflow shows up in the Crdr-Datum surface boundary creation when the surface is not continuous in the transverse direction. A divided highway is a good example of this scenario. The recommended workflow will require the user to create two surface boundaries:

  1. One that follows the outside subgrade shoulder points
  2. A second "hide" boundary that follows the median side subgrade shoulder points.

Alternatively, the user could create two separate Crdr-Datum surfaces; one for the NB/EB subgrade, and a second for the SB/WB subgrade.

Surface model deliverable impact

Since the result of the refinement surfaces is not changed, the impact to the surface model deliverable is not affected, with one exception.

Warning: Rural driveway surfaces should not be pasted into the Rfnt-Top surface. Since the Rfnt-Top surface is a component of the Rfnt-Datum surface, the rural driveways must be kept separately.

Contractors do not want the rural driveways to be part of the datum surfaces based on the workflow of their construction operations. The rural driveways surface is a separate surface model deliverable. See FDM 15-5-7 for additional details on design model requirements.