# PA Ramp Build Spec — reconciled

Written 2026-08-03 after research + measurement. Supersedes ad-hoc azimuth
tuning in `MapBuilder.luau`.

## Source conflict — READ THIS FIRST

Two sources disagree, and the disagreement matters:

| | Generic standard (AASHTO/FHWA/JP, via research) | Measured Daikoku (OSM circle fits) |
|---|---|---|
| Ramp form | short shallow **parallel slip road** | **loop helix**, 150–220° of turn |
| Radius | 80–120 m (285–430 studs) | 71–204 m, mean 131 m (**469 studs**) |
| Arc | 30–45° | 217° (main helix, rms 1.2 = truly circular) |

**Resolution: measured Daikoku wins for THIS build.** The generic spec describes
a typical roadside PA on a flat ground-level expressway. Daikoku PA is not that
— it sits at the bottom of a **five-level junction stack** on reclaimed land, so
its ramps are genuinely helical loops, not slip roads. The satellite plan view
(`aerial/daikoku_z19.jpg`) shows one large-radius arc sweeping around the lot.

The generic spec is still authoritative for the **merge detail** (below), which
is not Daikoku-specific.

## Numbers to build to

| Quantity | Value | Source |
|---|---|---|
| Scale | 3.571 studs/m (1 stud = 0.28 m) | project |
| Main entry helix radius | **525 studs** (147 m) | OSM way 32403901, rms 1.2 |
| Secondary helix radius | **440 studs** (124 m) | OSM way 779045459, rms 0.7 |
| Tight connector radius | 255 studs (71 m) | OSM way 32355896 |
| Turn direction | **clockwise (right) — BOTH ramps** | 6 of 8 OSM ways; video 「右、右」 |
| Divergence at merge | 2–5° (current build: 0.1–0.2°, tangent) | AASHTO/FHWA |
| Deceleration lane | 150–200 m before gore | AASHTO |
| Acceleration lane | 200–300 m after gore | AASHTO |
| Gore apex angle | < 5°, chevron-painted over 30–50 m | AASHTO |
| Superelevation | 4–8% bank on curves | AASHTO |
| Deck-to-deck spacing | 36–43 studs/level (10–12 m) | JP standard |

## Hard constraints (checkable in a probe)

1. **Entry and exit ramps must NEVER intersect.** Current build fails this:
   2547 point-pairs within 30 studs planar at < 12 studs dY, worst case
   **0.5 studs apart at dY = 0.0**. This is the dominant visual defect —
   it reads as a bowtie tangle. Probe must assert 0 such pairs.
2. Both ramps curve **the same direction** (clockwise). They are at opposite
   ends of the lot and wrap the same way; they do not mirror into each other.
3. Ramp arc wraps **outside** the parking apron, forming its boundary — it does
   not cut across the lot interior.
4. Merge is tangent (already achieved: 0.1–0.2°).
5. No ramp part intersects any Workspace-level building model (obstacle scope
   must be INVERTED, not a name whitelist — see verification skill).

## Edge / structure treatment (from onboard video + Commons photos)

- Edge = **low concrete jersey base + see-through chain-link mesh fence above**.
  NOT a tall solid parapet. Current build's heavy kerb chain is why the ramps
  read as thick white rails.
- **Red/orange chevron shoulder paint** through every ramp curve — present in
  all five reference videos, day and night. Cheapest high-value detail.
- Piers: **large cylindrical columns**, widely spaced, under a **trapezoidal
  box-girder** deck underside. White/pale concrete.
- White zebra hatching fills the gore wedge.