Public-private partnership (PPP)

A public-private partnership (PPP) is a long-term contract in which a private consortium finances, builds and often operates a piece of public infrastructure, gets paid over years — by the government, by users, or both — and hands the asset back at the end. The World Bank's working definition adds the test that matters: the private party must carry significant risk, and its payment must be linked to performance.

In this atlas, PPPs are mostly how streetlights, metros and fare systems actually got paid for. Washington D.C.'s 15-year streetlight P3 raised roughly $160m in private activity and revenue bonds, alongside about $150m of sponsor equity, to convert more than 75,000 lights. Montreal's REM shows a different payment shape: the driverless metro belongs to the pension fund's infrastructure arm, and the regional transit authority pays it a fee for every passenger-kilometre travelled.

The demand forecast is the whole deal. Busan's Gimhae light rail was let as a build-transfer-operate concession with a minimum revenue guarantee written against a forecast of 176,358 riders a day; 30,084 came, and the two cities paid 906.8 billion won in support between 2011 and 2025. A guarantee attached to an optimistic forecast transfers no risk — it only delays the bill. Contracts also outlive the technology they were signed for, which is why some fare systems here stay locked to one supplier for decades.