Run detail · gridlock-v1
Sonnet 4.5 made only 9 changes totalling $30k, but every one of them made congestion worse — junctions rose from 36 to 40, congested metres from 4,800 to 5,496, and population fell 9% to 28,631; composite 0.31 came almost entirely from the restraint terms because the congestion reward was zero.
What the agent did
Sonnet opened with parallel observations — city overview, metrics, and a full segment query — establishing baseline: flow 55%, 4,800 m of congested road, 36 jammed junctions, population 31,498. The query returned 104 segments at density ≥ 0.7, all at 1.0. Three separate map renders zoomed in on the main interchange cluster at x ≈ −300, z ≈ −690 to −860, the western interchange at x ≈ −650 to −830, and the southern residential district at z ≈ −1,820 to −1,960.
The diagnosis was correct: a spaghetti of 37 highway ramps at the main interchange, all maxed out, with queue spill backing the northbound city highway solid from z = −692 up to z = −352. Sonnet spent several thousand ticks studying node elevations, traffic directions, and dead-end stubs before formulating a plan.
The plan: four direct ramp connections to short-circuit the three-hop spaghetti paths at the main interchange — SB → EB highway, EB highway → NB city, WB highway → NB city, and SB → WB highway via a two-leg polyline routed around a HighwayRampPillar obstacle. Validation passed (total $30,047); all five segments were built in one apply_plan call. The new ramps snapped cleanly to existing nodes 31923, 26369, 16646, and 23536.
After 1,170 ticks (~2 in-game days), metrics read: flow 55.5%, junctions 45 (up from 40 at observation, up from baseline 36), congested metres 5,726 m. Sonnet noted this was expected churn during re-routing and stepped again.
After a second 1,170-tick step: flow 56.3%, junctions 43, metres 5,652 m, abandoned buildings 4. After a third step (1,755 ticks): flow 55.75%, junctions 38, metres 5,863 m, abandoned buildings 6. The junction count was oscillating but congested road metres were on a clear upward trend — nearly 1,100 m above baseline.
Sonnet re-queried congested segments and identified the problem: node 16646 now had three incoming ramps (the original pair plus the new EB→NB ramp) all merging into a single outgoing 6-lane segment that was already at density 1.0. Adding merge points to a saturated node had created friction that slowed through traffic more than the shortcuts helped.
Sonnet bulldozed segments 30072 (EB→NB at 16646), 18595 (WB→NB at 16646), 22578, and 32631 (the two-leg SB→WB polyline overloading the merge at node 23591). The one surviving segment was 4630 (SB→EB shortcut, density below 0.7 — not contributing to congestion but also not helping enough to offset the damage already done).
Immediately after the four demolitions, junctions ticked down to 37. A 1,755-tick step brought them back to 39 and metres to 6,003 m. A further 1,170-tick step pushed junctions to 41 and metres to 6,142 m. The system was not stabilising.
Sonnet observed the southern residential district (z ≈ −1,700 to −2,000), finding node 7685 as a three-way hub where basic road segments 2816, 7147, and 11811 all converged at density 1.0. An attempt to build a bypass connecting node 29116 to the eastern chain (13990 → 15594 → 29934 → 23113) failed with OBJECT_COLLISION on four buildings. A further attempt connecting 29116 to the eastern node 23113 also collided. The southern district was too densely built for new roads.
With no viable route to build, and congestion still at 6,202 m (42 junctions), Sonnet stepped the sim 2,340 ticks to wait for stabilisation — junctions fell to 39 and metres barely moved (+22 m over 4 days). Traffic flow reached 55.75%.
A final 1,170-tick step revealed the critical signal: population had crashed from 32,088 to 31,636 in two days — below the 31,498 starting count — and congested metres jumped to 6,370 m at 73 m/day (accelerating). Happiness had slipped to 81. Sonnet recognised the downward spiral and submitted immediately to prevent further livability damage.
The harness settled the run: flow 57.5 → 61.125 (a slight flow rise from the one surviving ramp), congested metres 4,800 → 5,496 (+14%), junctions 36 → 39, population 31,498 → 28,631 (−9%), health factor 0.79. The congestion-reduction reward was zero. The composite 0.31 was carried almost entirely by the spending restraint ($30k) and change-count restraint (9 changes) terms.