A new proposal calls for Brooklyn’s Grand Street to be closed to vehicular traffic and converted into a “peopleway” to make commuting easier during the L train shutdown.

The transit advocacy nonprofit Transportation Alternatives has begun rallying behind the idea as a way to increase safety, capacity and offer a more established Brooklyn connection to the Williamsburg Bridge, which is poised to play a vital role in absorbing L train riders during the 2019 shutdown.

“Grand Street’s a popular route for Brooklynites traveling to Manhattan,” said Caroline Samponaro, deputy director of Transportation Alternatives. “It’s a straight shot to the bridge and is a wide enough street with space to work with. We can make better use of that public space.”

A reimagined Grand Street might help some of the 225,000 straphangers who take the L train between boroughs each day. They’ll be stranded in 2019 when the MTA shuts down Manhattan L service order to make necessary Superstorm Sandy-related repairs to the line’s Canarsie Tunnel.

Transportation Alternatives is eyeing the conversion for a 1.5-mile route along Grand Street, from Metropolitan Avenue to Borinquen Place. While the idea is in its nascent stages, the concept would prioritize bus traffic and give cyclists better, protected bike lanes. Between 10,000 and 13,000 people use that Grand Street corridor each hour, according to city DOT data.

With the redesign, the advocacy group estimates that the street will be able to carry 33,000 people per hour by getting cars out of the way of high-capacity buses. Grand Street would serve as a compliment to the Manhattan version of this proposal; several transit groups have called to eliminate vehicular traffic from 14th Street during the shutdown, which would create a busway to mimic the L train service below.

“This is about using shutdown an opportunity to better serve transit riders, bike riders and pedestrians” on city streets, Samponaro said.

Both projects would require the collaboration of the city Department of Transportation, overseer of city streets, and the MTA, which runs the buses on those streets.

“As we continue our traffic modeling and other studies related to the Canarsie closure, we welcome ideas from others, and will gladly discuss ideas with DOT and other stakeholders,” said MTA Spokesman Kevin Ortiz in a statement.

14th Street, lined with institutions and chain stores, is a much different scene from Grand Street’s row houses and small businesses ranging from ethnic restaurants, delis and pet shops, to taverns and dimly-lit bars.

Business owners and cyclists who are open to the idea complained that trucks heavily use the local street as a thoroughfare to get from the Williamsburg Bridge to Queens.

“I’ve always felt that there’s been too much truck traffic and that traffic has really kept the neighborhood from being as charming as it could be,” said Stephanie Schneider, owner of the Huckleberry Bar on Grand Street.

Gigi Lee, whose father has owned Lee’s Furniture on Grand for 17 years, said she believe something needs to be done to mitigate traffic even though the furniture store is trucking merchandise in and out of the shop between 10 a.m. and 7 p.m.

“Without the L train, there’ll just be too many people trying to use this street,” Lee said. “It’ll be a problem.”

On the stretch of Grand this year, there have been nine recorded traffic injuries and two traffic fatalities, according to city data, including the high-profile death of the 35-year-old Queens cyclist Matthew von Ohlen, who was hit and killed by a driver as he pedaled through Grand’s bike lane.

Transportation Alternatives plans to meet with more businesses and local elected officials to gain support. The office of Councilman Antonio Reynoso, who has called for the city to install protected bike lanes on the street after von Ohlen’s death, refrained from commenting on the proposal until it’s heard more details from the group. Homer Hill, of the Grand Street Business Improvement District, refrained from commenting for the same reasons.

“Grand Street, as it is, needs an improvement anyway,” said Amanda Stosz, 32, a Clinton Hill resident and friend of von Ohlen, who has regularly commuted on Grand Street in the past for her photography industry job. “There’s just going to be even more bike commuters, more pedestrians who would normally take the L train trying to get into Manhattan.”