MARTA — the Metropolitan Atlanta Rapid Transit Authority — was created by state law in the 1960s and began rail service in 1979. Its structure is unusual: the authority was set up so that its operations had to be funded largely out of fares and a local sales tax, a constraint that made expansion politically and financially difficult from the beginning.

Why the map looks like this

Only Fulton and DeKalb counties joined the system when it was formed; most of the surrounding counties stayed out, and later votes in other counties failed. The result is a rail network that mostly serves the city and its two core counties, and a bus network that carries the riders with the least political leverage. A majority of MARTA's riders are Black, and the system's busiest corridors run through Black Atlanta.

Who pays for it now

In 2016, City of Atlanta voters approved a sales tax dedicated to expanded transit, and the city — not the state — became the largest single funder of new service inside its own boundaries. That changed who gets to decide, and made the city's transit future a city question first.