Parametric Road Design for Practical Road Construction

Parametric Road is an open-source, FreeCAD-based road design platform that automates alignments, profiles, corridors, cross-sections, earthwork quantities, and BIM-ready outputs.

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Inspiration

Parametric Road was inspired by the high cost, limited flexibility, and proprietary workflows of conventional road-design software. We wanted to create an open and programmable alternative that could automate practical road modeling using FreeCAD and Python.

What it does

Parametric Road is an open-source road-design platform that automates:

  • Horizontal and vertical alignments
  • Existing and finished-grade profiles
  • 3D centerlines
  • Parametric cross-sections
  • Corridor modeling
  • Cut and fill analysis
  • Engineering and BIM-ready outputs

Its core workflow is:

Terrain
→ Alignment
→ Profiles
→ 3D Centerline
→ Assembly
→ Cross-Sections
→ Corridor
→ Quantities

How we built it

We developed Parametric Road as a custom FreeCAD Workbench using Python and the FreeCAD API.

The system combines horizontal alignment coordinates with vertical elevations by station to generate a 3D centerline:

[ \mathbf{C}(s)= \begin{bmatrix} x(s) \ y(s) \ z(s) \end{bmatrix} ]

Road assemblies are placed along the centerline, oriented to the local road direction, and connected to create corridor geometry. CSV and LandXML workflows are also used for data exchange and testing.

Challenges we ran into

The main challenges included:

  • Combining horizontal and vertical geometry accurately
  • Maintaining stable cross-section orientation along curved 3D paths
  • Preventing twisted or invalid loft geometry
  • Creating valid shells and watertight solids
  • Managing FreeCAD object dependencies and recomputation
  • Calculating reliable cut and fill quantities from terrain data

Accomplishments that we're proud of

We successfully built an integrated parametric workflow that connects terrain, alignments, profiles, 3D centerlines, assemblies, cross-sections, and corridor models.

We are especially proud that the project can generate road geometry from engineering parameters instead of relying on repetitive manual modeling. It also demonstrates that FreeCAD can be extended into a practical civil-engineering platform.

What we learned

We learned that road design software requires more than visible 3D geometry. Reliable topology, object dependencies, recomputation order, and engineering outputs are equally important.

We also learned how civil engineering rules, computational geometry, parametric CAD, and open data standards must work together in one consistent system.

What's next for Parametric Road Design for Practical Road Construction

The next stage is to make Parametric Road suitable for practical road-construction workflows by adding:

  • Superelevation and crossfall
  • Cut and fill side slopes
  • Intersections and ramps
  • Drainage structures
  • Automated cross-section drawings
  • Quantity and earthwork reports
  • IFC 4.3 and OpenDRIVE export
  • Watertight solid validation
  • AI-assisted design review and automation

Our long-term goal is to make road design more open, programmable, reproducible, and accessible.

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