# Combined city drive mode (r343)

## Runtime

The main viewer accepts `world=combined`. It loads 14 gzip chunks for the deduplicated union of the eight exported region
meshes, then assembles the 163 MiB GLB in memory. The uncompressed source is
`reverse-engineering/city-bayview-combined-candidate.glb`. The normal Region selector remains active: it chooses the
route, traffic, light, barrier, and marker data while the full combined mesh
continues to provide visible scenery and road support. The browser transfers 89.48 MiB across 14 gzip chunks with gzip support;
browsers without `DecompressionStream` fall back to the raw 163 MiB chunks.
First load remains heavier than selecting one region.

## Chrome captures

- L4RA Route 736 reached `City scene ready` with no page error, 77,603 nearby
  triangles, and the r341 authored lane offset of 1.8056 m.
- L4RB reached `City scene ready` with no page error, 68,832 nearby triangles,
  229 nearby textures, 99 routes, and 12 ambient vehicle body models. The view
  is on a raised divided road with source dashed markings and a traffic car
  ahead.
- A 1.8-second W hold in the combined L4RB view moved the car from
  `(24.01, 743.58)` to `(28.95, 741.17)` while retaining road support and the
  ready state.

The views show no obvious building crossing the selected pavement at these
two points. This is still an experimental visual union. Some same-transform
regional placements have different payloads, and the union has not been
audited across the complete map for overlapping surfaces or wrong placement.

## Route and traffic scope

The viewer still loads route, traffic, lighting, and other regional records
from the selected region. The combined mesh makes the whole exported road
surface available to the player's existing road-support movement, but the
traffic graph has not been made continuous across region files. Raw route IDs
are reused between regions, so a unified graph needs namespaced route identity
and verified transitions before the viewer can safely join regional traffic
paths. L4RH and L4RR have no recovered free-roam routes.

This mode does not establish retail steering or suspension response; see
[`route736-start-lane-review-r341.md`](route736-start-lane-review-r341.md) and
[`driving-feel-review-r340.md`](driving-feel-review-r340.md).