Even with its increased Gold bonus in Rise and Fall, chances are you won't get much use out of Public Transport. If you're trying to build the largest cities possible (or you just want places to build Food Markets and Shopping Malls), it could be worth slotting until you've replaced your Farms with Neighborhoods and then immediately swapping it out for something less situational.
Civilopedia entry Edit
Public transport – in Asia, run as profit-driven, privately owned enterprises; in the Americas, generally as government operations; in Europe, a mix of state-owned and private companies – provide inexpensive passenger services to the general public … buses, subways, trams, commuter trains, ferries, and such. The first such organized system appears to have been the omnibus service that operated in Paris commencing in 1662, but it didn’t last long. Omnibuses were reintroduced in Nantes in 1826, and in London in 1829. Shortly thereafter, as London became more crowded and unsanitary, good folk began settling in “suburbs” around the city, a development helped by the creation of the Metropolitan Railway in the 1860s which offered cheap fares into the heart of the capital. Soon, every industrial city wanted a public transit system too.