The MTA is resurfacing a long-dormant idea to bring transit service to existing freight train tracks running from Bay Ridge all the way up to Astoria .

The agency on Thursday awarded a $1.3 million contract to AECOM, an engineering firm, to study the feasibility of the sprawling project, which would stretch 16 miles and pass near 19 subway lines and the Long Island Railroad. If implemented, it would represent that largest expansion of the city's transit capacity since World War II.

“This project is hugely exciting—partly because it is based on the concept of squeezing more out of our already existing infrastructure so we don’t always have to build new subway lines from scratch,” MTA Chief Development Officer Janno Lieber said in a statement.

The "Bay Ridge branch," as the MTA is calling it, would begin at the south Brooklyn waterfront, passing Brooklyn College then running parallel along the L line from East New York to Broadway Junction and Bushwick, before turning into Queens and heading up toward Roosevelt Avenue/Jackson Heights and eventually Astoria. Potential connections would exist to N, F, Q, 2, 5, L and M trains.

A similar idea known as the Triboro RX line was first proposed by the Regional Plan Association in 1996. That version would have extended into the Bronx, with the new line stretching over the Hell Gate Bridge to meet the 6 line in Hunts Point.

The new line being studied would pass through several transit-starved neighborhoods—including East Flatbush, Brownsville and Maspeth—and is expected to serve some 76,000 riders daily, roughly 50 percent more than Mayor Bill de Blasio's $2.7 billion streetcar plan, which was also recently resurrected. About half of the Bay Ridge line's riders would be people who don't typically ride the subway, according to some modeling.

A map of the MTA's proposed Bay Ridge branch that is being studied.

A major obstacle, as always, is funding. The Regional Plan Association has previously pegged the project between $1 and $2 billion—not exactly cheap, though less painful when you consider we recently spent $1.5 billion to extend the 7 train into Hudson Yards.

There are also some concerns about adding subway service to an active, if underutilized, freight line. Rep. Jerry Nadler threw cold water on the idea back in 2013, telling Gothamist the proposal was "not compatible" with the existing Bay Ridge freight line due in part to scheduling conflicts.

Meanwhile, cities like London and Chicago have found a way to share freight and passenger service on a single set of tracks. And while it'll be years, at least, before the project gets off the ground, transit experts say there is reason for optimism.

“Regional Plan Association is thrilled that the MTA is moving forward on this study, which is the crucial first step to realize our Triboro vision," said RPA President Tom Wright. "Transit service on the Bay Ridge Line would not only provide better transit service between the outer boroughs but also cut construction and acquisition costs since the rail tracks are already there."

In the meantime, you can build your own dream subway extension here.