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Level of Detail

The following information supplements PDDM Section 9.6.1.

Digital Design Data

Develop highway design surveys and road designs using Bentley GEOPAK and/or(?) Open Roads software. Provide design data in native MicroStation file formats compatible with these programs. These may include:

  • MicroStation design files (DGN files) including plan and profile view geometry and cross-sections;
  • Existing ground terrain models as a Triangular Irregular Network (TIN) in both GEOPAK TIN and Land XML formats;
  • GEOPAK Coordinate geometry data provided in its native GEOPAK format (GPK files); and
  • 3D digital design model representing the proposed finished grade surface (and other secondary surfaces when applicable) in GEOPAK TIN, Land XML and InRoads DTM formats.

Adhere to current FLH CADD standards. Submit a Design File Log listing all files with a description of the file's content (i.e. GPK file with all chains and profiles listed, DGN files, etc.). Specify the coordinate system, datum and any project projection factors used to establish mapping control. Obtain coordinate systems, datums and projection factors from the original base map.

MicroStation Design files contain 2D or 3D proposed plan and profile view or cross-section geometry. Plan view geometry includes items such as pavement edges, shoulders, curbs, gutters, sidewalks, retaining walls or any other feature used in the generation of a 3D model. Cross-section geometry refers to the master proposed cross-section files (not the cross-section sheets) for all alignments found in the GPK file, if applicable. Proposed cross-section files are required to include the GEOPAK cross-section cells. The files include all existing ground lines including subsoil conditions, proposed templates including all pavement, shoulders, curbs, gutters and sidewalks, and all other side slope conditions.

Existing Ground 3D Model represents the existing ground conditions as provided by FLH, third party surveyor or a combination of both. The file is submitted both in the native GEOPAK TIN and LandXML format.

Coordinate Geometry Data contains all final alignments used in the development of the contract plans. Alignments include all chains, existing and proposed profiles, control points and any special profiles used for drainage purposes or other design features such as sidewalks, retaining walls, etc. Remove all preliminary alignments from the coordinate geometry file. Create descriptive names for all geometry contained in the GPK file that are representative of the designed alignments and features found in the plans. Provide the coordinate geometry information in both the native GEOPAK (.gpk) format and the LandXML version.

Superelevation Transitions: Submit files containing all transition points showing stationing, cross-slopes, superelevation rates, runoff lengths and runout tangent lengths. Submit the superelevation transitions in ASCII text format as generated using the GEOPAK superelevation tools. In addition, include the MicroStation pattern-shape file generated using the GEOPAK superelevation tools.

Submit an all-inclusive 3D Digital Design Model of the project corridors as a design data deliverable. At a minimum, create surfaces representing the proposed finished grade AND a surface representing the subgrade, or top of aggregate (both should daylight to the side slopes). Submit the 3D digital design models in the GEOPAK TIN or OpenRoads DGN, and LandXML formats.

3D Model Application During Design Development

Exhibit 9.6.1A-1 illustrates the types and uses for 3D design data reviewed during any stage of the project design. Each design stage adds additional model elements and uses; therefore continue to check information for prior stages.

Exhibit 9.6.1A-1: Design Model Usage During Milestones
Design Stage3D Design Model Elements3D Design Model Uses
Preliminary DesignExisting conditions surface
Low density proposed surfaces
Proposed roadway corridor model
Existing utilities
Design results due to avoidance of sensitive resources such as cultural and wetlands
Quantify impacts on sensitive resources, if any
Minimize ROW impacts
Compute quantities
Plan surface drainage
Create preliminary plans and estimate
Intermediate DesignMedium density proposed surfaces
Proposed structures (external faces)
Existing and proposed utilities
Storm drainage systems
Site distance checks
Visual impact analyses
Earthwork quantities
Interdisciplinary design coordination
Staging and constructability review
Minimize utility relocations (clash avoidance)
Plan-In-Hand DesignHigh density proposed surfaces
Proposed structures
Proposed utilities
Storm drainage systems
Surface drainage review
Create 3D graphics and 4D videos for ROW
Acquisition and Public involvement
Compute quantities
Maintenance of Traffic conceptual plans
Create ROW and utility relocation plans
Final PS&E DesignVery high density proposed surfaces
Proposed structures (major systems)
Final Storm drainage systems design
Design validation and interdisciplinary review
Compute final quantities
Maintenance of Traffic review
Create final contract plans and estimate
Create 3D model reference data
PS&E ApprovalVery high density proposed surfaces
Final roadway corridor model
Final structures (major systems)
Final proposed utilities
Final storm drainage systems
Create contract documents
Create staking/layout design
Create AMG/real-time verification models

Level of Details for 3D Data

Each project type requires different features and a varying Level of Detail (LOD) to depict the design intent sufficiently accurately for 3D design reviews and use during construction. Due to schedule, scope, and/or budget constraints, the level of detail of the 3D data requirements may be left to the discretion of the design project manager. During the course of design it may be necessary to obtain additional data or to increase the level of detail of data previously collected.

There are various methods to create 3D models of highway design features:

  • Corridor Model – typical sections created (in GEOPAK Corridor Modeler) based on parametric rules placed at defined stations (template drops). This is the most common tool for modeling linear elements that are generally regular in shape parallel to the alignment. Standard uses of corridor models include roadways and ditches. Advanced uses of corridor models include retaining walls, bridge abutments and intersections.
  • String Model – uses rules (in Open Roads) to offset linear features horizontally and vertically. This is a common tool for modeling non-linear features that follow consistent rules perpendicular to the base feature. Standard uses of string models include drainage basins and parking lots. Advanced uses include intersections and lane transitions.
  • Feature Modeling – these 3D line strings can be either created manually or output from corridor or string models. This is a common tool for hand-grading small areas like around headwalls. Add features to surfaces as break lines.
  • Subsurface Utility Modeling – GEOPAK Drainage visualizes single bore pipes in 3D. Bentley Subsurface Utility Design and Analysis (SUDA) creates 3D models of subsurface utility pipes and structures of predefined shapes and dimensions. These models follow parametric rules to modify depths and lengths as structure inverts or locations change. They also are able to compute storm sewer hydraulics and incorporate design changes in the 3D model. The pipes and structures function as 3D Solid Models.
  • 3D Solid Modeling – other 3D elements usually created manually. A library of 3D solid model elements like standard headwalls, light standards, sign posts and other structures is under development.
Exhibit 9.6.1A-2: 3D Model Features
FeatureDesign MethodData Type
RoadwaysCorridor ModelAlignment, Surface & 3D Line Strings
Side SlopesCorridor or String ModelSurface & 3D Line Strings
Gore AreasCorridor, String or Feature ModelingSurface & 3D Line Strings
Intersections & InterchangesCorridor or String ModelAlignment, Surface & 3D Line Strings
Sidewalks & Bike PathsCorridor or String ModelSurface & 3D Line Strings
Lane Width TransitionsCorridor or String ModelSurface & 3D Line Strings
Headwall GradingString ModelSurface & 3D Line Strings
Guardrail Berm TransitionsCorridor, String or Feature ModelingSurface & 3D Line Strings
Benching TransitionsCorridor, String or Feature ModelingSurface & 3D Line Strings
Bridge AbutmentsCorridor or String ModelSurface & 3D Line Strings
Bridge Substructures3D Solid Modeling3D Line Strings
Bridge Superstructures & DecksCorridor, String or Feature ModelingSurface & 3D Line Strings
Stormwater Ponds, Ditches & SwalesString or Feature ModelingSurface & 3D Line Strings
Drainage & Utility PipesSubsurface Utility Model3D Solid Models
Drainage & Utility StructuresSubsurface Utility Model3D Solid Models
Pavement MarkingsCorridor, String or Feature Modeling3D Line Strings
Curb & GuttersCorridor, String or Feature Modeling3D Line String (flow line)
3D Line String (top of curb)
Retaining WallsCorridor, String or Feature Modeling3D Line Strings

The following table details design features to be completed by milestone along with the optimal data density:

Exhibit 9.6.1A-3: Design Features Data Density by Milestone
FeaturePreliminary DesignPlan-In-Hand DesignFinal Design
Roadways – Top of Surface
Roadways – Interim Surface
Roadways – Subgrade Surface
Roadways (Data Density)10 ft [2.5 m] in curves
25 ft [5 m] in tangent
10 ft [2.5 m] in curves
25 ft [5 m] in tangent
1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Side Slopes10 ft [2.5 m] in curves
25 ft [5 m] in tangent
10 ft [2.5 m] in curves
25 ft [5 m] in tangent
1 ft [0.25 m] curves
5 ft [1 m] in tangent
Gore Areas10 ft [2.5 m]10 ft [2.5 m]1 ft [0.25 m]
Intersections & Interchanges10 ft [2.5 m] Intersections
25 ft [5 m] Interchanges
10 ft [2.5 m] Intersections
25 ft [5 m] Interchanges
1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Medians & Cross-overs1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Sidewalks & Bike Paths1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Lane Width Transitions10 ft [2.5 m]10 ft [2.5 m]1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Headwall Grading1 ft [0.25 m]
Guardrail Berm Transitions1 ft [0.25 m]
Benching Transitions1 ft [0.25 m]
Bridge Abutments1 ft [0.25 m]
Bridge Substructures1 ft [0.25 m]
Bridge Superstructures & Decks1 ft [0.25 m]
Stormwater Ponds, Ditches & Swales25 ft [5 m]25 ft [5 m]1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Drainage and Utility Pipes
Drainage and Utility Structures
Pavement Markings25 ft [5 m]25 ft [5 m]1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Curb & Gutter25 ft [5 m]25 ft [5 m]1 ft [0.25 m] in curves
5 ft [1 m] in tangent
Retaining Walls10 ft [2.5 m]10 ft [2.5 m]1 ft [0.25 m] in curves
5 ft [1 m] in tangent

Note: The maximum recommended intervals are shown; density may be lowered based on the Project Manager's discretion.

Updated: Monday, March 28, 2022