The Demand Engine

Every coin you earn is a delivered passenger, and passengers are generated by a gravity model with three strict rules. Understand these three and you understand where your money comes from.

Rule 1 — Trips only flow between different-coloured stations

Every station is automatically assigned a colour. There are six colours; the first six stations each get a distinct one, and from the seventh onward the colours recycle. A passenger boards at one station wanting to reach a station of a different colour.

The consequence: a line where two neighbouring stations share a colour generates zero trips between them. This is the silent killer behind "I built loads of stations and made no money" — past six stations you start pairing same-coloured stops that can't trade with each other. (More than six stations is still fine — a seventh still trades with every station of a different colour — it just can't trade with its own-colour twin.)

Rule 2 — A station only "sees" 2 cells

Each station scans a 2-cell radius (king-moves) around itself. A building's contribution falls off with distance:

So a building more than two cells from every platform earns you nothing at all — but still bills its full upkeep every period. Pack your homes and workplaces tight to the line. (A building counts for every station within range, so two stations placed too close both draw on the same few buildings — another reason not to overlap stops needlessly.)

Rule 3 — Demand is workers × jobs, balanced

Each building type feeds the gravity model:

Commuter demand across the network behaves, in effect, like:

demand ≈ total Jobs × min(total Workers, total Jobs)

It is maximised when workers and jobs are balanced (W ≈ J). The key asymmetry to keep in mind:

• Surplus workers are dead. Once you have more workers than jobs, extra houses add no commuter trips at all — they're flat in the formula. They still cost upkeep.
• Surplus jobs are merely under-used. More jobs than workers still adds demand, but your low worker count is the bottleneck and the extra job capacity is upkeep you're not fully using.

Because a House supplies 2 workers and a Factory offers 10 jobs, the balance point is roughly 5 houses per factory (Office Blocks soak up even more — about 2.5 Apartments per Office). A common mistake is "two-thirds houses, one-third workplaces": with those weights that's actually worker-short, leaving your demand below what your job capacity could support. Match the two sides.

Parks are the third axis. Trees and shrubs generate weekend leisure trips, and that channel has stronger gravity than the weekday commute. A green station that workers travel to is a genuine income stream — not just decoration — and it isn't capped by jobs.

The cap that ends over-building

The per-phase demand pool is capped by era — 20 (Steam) → 45 → 100 → 200 (Modern). Once your workers × jobs are large enough to hit that cap, more buildings add zero income but keep adding upkeep. This is the point where a smart player stops adding catchment and spends instead on a bigger train (to actually collect the capped demand) and on land (to make each trip pay more).

Knowing that you've hit the cap is the whole game's turning point — covered next in Stations, Trains & Throughput.