The asphalt edge

Where the pavement ends · output = clean CAD polylines · High confidence Low–Med effort

The edge isn't an object standing on the road — it's the boundary of the road itself. And since we already extract the road surface, step one is nearly free: trace its outline.

The Autobahn twist: usually no curb

Most textbook "road edge" methods hunt for the height step of a kerb. On the German motorway that step usually isn't there — the asphalt simply meets gravel or grass at the same height. So the height signal, the star of the curb literature, is benched.²⁷ The edge is still perfectly visible — but as a change in texture, not height.

The pavement doesn't drop — it just turns bumpy. So the strongest signal is roughness: asphalt is locally flat and smooth; grass and gravel scatter the laser.

Which signals are reliable?

Signal	Useful here?
Roughness (smooth vs bumpy)	✅ Strongest cue on a curbless edge
Point density	✅ Changes at gravel / vegetation
Slope	◐ Helps at gutters & embankments
Brightness (asphalt is darker)	◐ Only locally — never as a fixed threshold³⁰
Height step	✗ Usually absent on the Autobahn

The brightness caveat matters: laser brightness depends on distance, angle and the sensor itself, so the same asphalt can read light in one scan and dark in another. "This side is darker than that side, right here" is safe; "asphalt is below value X everywhere" is a trap.³⁰

The proposed pipeline

Outline the road surface we already extract — draw the boundary of the surface points. A good first draft for free.
Walk along the road and refine — every metre, look at a thin slice across the road and snap the edge to the strongest roughness / density / slope change.
Smooth & simplify — tidy the wobble and thin the points into clean left/right lines (standard Python: SciPy, Shapely).
Export CAD polylines — the same deliverable format as our road markings.

⚠ One rule with teeth At exits and on-ramps, do not bridge the gap. The edge genuinely branches there; an algorithm that "helpfully" connects across a slip road is inventing geometry. Fill only short gaps (a parked truck's shadow) where both sides clearly line up.

➜ Recommendation & first experiment Start with the free part: outline the road surface on a few finished segments and simply look at how well it hugs the true edge. That one afternoon tells us whether we need the full slice-refinement step everywhere or only at trouble spots — and settles the open question of whether concrete gutters (Rinne) get swept into the surface.