Curitiba bought garbage with bus tokens and food

By the late 1980s Curitiba's population had grown twentyfold in five decades and its favelas — narrow, unplanned, truck-proof — were drowning in uncollected garbage, with disease following. The customary fixes, widening roads or bulldozing, needed money the city simply did not have. Jaime Lerner's team worked under a standing rule: no money means more creativity, not less ambition.

Câmbio Verde inverted the problem: instead of sending trucks in, it paid residents to bring garbage out — a bus token for a bag of sorted trash, food parcels bought from surplus-crop farmers for recyclables, notebooks for school paper drives. Three unsolvable problems (garbage, transit access, farm surpluses) were paired into one trade.

Jaime Lerner's city paid for pre-sorted trash bags with bus tokens, and paper with food chits — pairing the waste problem with the mobility and food problems instead of solving any of them head-on.

Paid residents with bus tokens for sorted trash and food chits for paper, so they carried waste out—using existing transit and farm surplus as currency.

Residents could carry trash where trucks couldn't go, so the constraint was the truck, not the trash.

Bus tokens were already issued, so paying with them cost no new cash.

Surplus food was already subsidized, so it was a cheap currency for recyclables.

Each trade cleared because one side's abundance was the other's lack, creating mutual incentive.

When several problems are each unfundable alone, look for a barter where each side's surplus is the other's need, so the exchange funds itself.

The 62 poorest neighbourhoods traded 11,000 tonnes of garbage for nearly a million bus tokens; schools traded 200 tonnes for 1.9M notebooks; the Câmbio Verde runs to this day. The 62 poorest neighbourhoods traded 11,000 tonnes of garbage for nearly a million bus tokens; over one three-year stretch schools swapped 200 tonnes for 1.9 million notebooks. The programme still runs, and 'align two problems until they solve each other' became the signature of Curitiba's whole planning school.