Transit advocates hope the MTA will invest in opening closed subway entrances in North Brooklyn before the L train shuts down as a way to brace for people using alternative lines and transfer routes. View Full Caption DNAinfo/Gwynne Hogan

WILLIAMSBURG — Closed subway staircases and entrances in North Brooklyn, which were shuttered years ago to cut costs, should be reopened to brace for the looming L train shutdown between Manhattan and Brooklyn, transit advocates say.

There are currently ten closed entrances and 27 staircases blocked off along the G, L, J, M and Z lines in North Brooklyn, the MTA confirmed.

And while advocates have been working with local politicians to push the MTA to reopen the defunct staircases and entrances for years citing surging ridership, news that L train service will be disrupted between Manhattan and Brooklyn for between 18 months and three years has given them a renewed sense of urgency, they said.

"This is an opportunity for MTA to do something now that will help out when the L train shut down happens," said Alan Minor an organizer for Neighbors Allied for Good Growth. "More people will be taking the J, M, Z. More people will be taking the G."

"These lines have just a shockingly high number of closed entrances and staircases," Minor said.

Along the above-ground J and Z line, straphangers may be familiar with gated staircases at 12 locations along Broadway, according to the 2014 data.

But more inconspicuous, are the covered staircases that you could pass by every day and never notice unless someone pointed them out to you, Minor said.

"[They're] hidden in plain sight."

Take the Metropolitan and Lorimer G and L stop, a transfer station that could see a huge bump in riders switching to the G train if the L doesn't run into Manhattan.

That Williamsburg station has six closed staircases and one closed entrance, according to the MTA.

On either side of Union Avenue where Hope and Powers streets intersect it, there are two yellow grates emblazoned with the words "Subway Keep Clear."

On the corner of Grand Street and Union Avenue, there's another metallic grate with the same words, and across Union from that, Minor suspects, is one staircase that's been sealed with concrete.

MTA spokesman Kevin Ortiz confirmed the agency was looking into reopening closed entrances and staircases, but didn't elaborate.

"As part of our efforts to accommodate growing ridership, we are studying and evaluating closed access points throughout the subway system and we’re looking at every idea for how to provide alternate service to L customers during any potential shutdown," Ortiz said.