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Transit honchos are considering a new billion-dollar passenger train that would run through southern Brooklyn, Queens, and the Bronx in an effort to better serve the transit-starved outer-boroughs, authorities announced on Oct. 15.

“Over the last 15 years, over half of job growth has been in the outer-boroughs,” said Maulin Mehta, a senior associate at the Regional Plan Association, which first proposed the commuter rail in 1996. “But right now, a lot of the train service is very Manhattan-centric.”

The Metropolitan Transit Authority will test the feasibility of retrofitting a series of pre-existing freight lines for use ferrying commuters, offering crosstown service from the Brooklyn Army Terminal in Sunset Park to East New York, before veering north parallel to the L line through Brownsville and Bushwick, and on to distant Queens and the Bronx.

The train, which the Transit Authority has dubbed the Triboro Line, would make 11 stops at new and preexisting stations in Brooklyn, providing connections to the R, N, D, F, Q, 2, 3, 5, and L trains. In all, the train would make 22 stops between Brooklyn Army Terminal and Co-Op City in the Bronx.

Brooklyn trains would travel on the Bay Ridge Branch — a freight line that is currently owned and operated by Amtrak, Long Island Railroad, and freight operator CSX.

The recently-announced study will examine the feasibility of roughly half the route from Brooklyn to Ridgewood, Queens, and would determine the project’s potential construction costs, impacts on the community, and frequency of service, according to Mehta.

Support for the Triboro Line ramped up after Assemblywoman Latrice Walker (D-Brownsville) proposed a bill calling on the Metropolitan Transit Authority to conduct a study for the project in June.

Sadly, the project’s hefty price tag makes the Triboro Line a distant reality at best — Mehta pegged the projected cost between $1 billion and $2 billion, which would eat up a sizable chunk of the transit authority’s $5.7 billion budget for all LIRR-related work in its 2020-2024 Capital Plan.

Another recent MTA study revealed that a similar proposal to restore passenger service along an existing Rockaway line would cost a jaw-dropping $6.8 billion, NY1 reported.

The Bay Ridge Branch rail line hasn’t carried passenger trains since 1924, but urban planners say that the freight line is well-suited for the project because its tracks are currently underutilized, and the existing infrastructure would help keep costs down relative to building new tunnels.

And while no other passenger trains in the city share rails with freight lines, Mehta claimed that the practice is common in other big cities.

“London and Chicago have commingled freight and passenger service, and have had success,” he said.

The Transit Authority’s study will begin by the end of the year, according to MTA spokesman Aaron Donovan.