# South Tower railway clearance follow-up

The earlier zero-intersection result checked only the two rail lines. It did not
test the space between, beside or above them. It therefore missed visible
conflicts between the approximate railway corridor and the modeled steel.

`check_path_clearance.mjs` now checks oriented solid boxes against the actual
production steel triangles. The **9-ft width and 12-ft height are diagnostic
choices**, not a sourced train clearance gauge or a tunnel diameter. Reference
markers and connection symbols are excluded. Thin steel between the rails and
at body height are explicit regression witnesses.

The SKA12/84 source rereading adds approach controls for Tracks 2 and 4 near the
northeast corner. No survey registration, structural member workpoint, section
envelope or rail elevation was changed. With the same diagnostic volume, the
previous trace flags six path/member pairs; the revised trace flags three:

- Track 2 / east column 301;
- Track 2 / east M5 left return strut;
- Track 2 / north M5 right return strut.

The subsequent [Book 1 corner correction](../south-corner-review/README.md) checks SB-125–128 and 1-B2-52/53. The two northeast M5 returns were modeling errors: neither source elevation shows them, and real corner connections cross the chamfer diagonally. After correcting the corner topology and replacing the eight terminal-column placeholders with their scheduled plate sections, the same probe flags **one** component: Track 2 / column 301. The railway and probe dimensions are unchanged.

This remains an unresolved model conflict, not evidence of a historical collision. Do not shrink the probe or invent a grade to claim clearance. Cross-source registration, track setting-out and approach grade still require verification.

The focused [column 301 measurement](../path-301-review/README.md) quantifies the current result: the closest rail line clears steel by 12.8 in, while the unchanged diagnostic width overlaps by 13.0 in. The overlap corresponds to about 1.5 pixels in the tracing frame. This scale comparison does not prove clearance or justify a corrective offset. The original raster comparison and measured finding are now available in the South Tower inspection; all geometry remains unchanged.

`rail-baseline.json` freezes the older terminal; `south-corner-review/baseline-components.json` freezes the earlier steel. `verification.json` reports three stages: six conflicts before the rail rereading, three before the corner correction, and one after the corner correction. The South Tower inspection includes nearby rails clipped from the shared source polylines without separate placement.

## Old tube versus later terminal

R-74 labels an existing south PATH tube passing east-west through the core.
[Book 3, drawing 3-B3-8, PDF page 138](https://archive.org/download/WTCI000013L/WTCI-000013-L.PDF#page=138)
specifies removing temporary trusses 607 and 907 and installing permanent columns
when that tube is removed. It separately identifies 507, 707, 806 and 1007 as
permanent transfers. Their retained openings do not establish an active tube in
the completed building. The later SKA12/84 terminal route is a different
arrangement. The old tube has **not** been inserted into the completed model.

Tamaro's 2002 account gives a nominal 17-ft tube diameter, but no vertical survey
through this core was recovered in this pass. A historical tube volume is not
part of this completed-state reconstruction.

Run `build_sublevels.py`, `build_slurry_wall.py`, `check_path_plan.py` and
`build_structural_details.py`, then `node tools/check_path_clearance.mjs` and the
South frame / core / tower integration checks. The source preservation review is
`tools/review_path_reconciliation.py`. No browser or GPU inspection was performed.