Manhattan’s 14th Street would be shut to all private vehicle traffic and “reserved exclusively for pedestrians, cyclists and two dedicated bus lanes” during the coming L train overhaul if the Regional Plan Association’s comprehensive recommendations are adopted.

This week, the think tank issued a report recommending that the MTA exploit the opportunity presented by planned repairs to the Canarsie tunnel to completely shut down the entire overburdened line for 14-18 months to permit a batch of upgrades that will forestall future shutdowns.

The RPA wants the MTA to repair stations, add needed entrances, widen platforms, boost electrical power and increase train storage capacity to better handle the 300,000 passengers a day the L train now shuttles.

Under the new RPA recommendations, “no private vehicles would be permitted” on 14th St. from Union Square. That’s so the masses of buses needed by inconvenienced commuters and other riders will have easier passage.

“Trucks would be allowed to make deliveries in this area overnight, and loading zones would be provided on adjacent avenues north and south of the intersections during the day, displacing on-street parking,” during daytime, according to the report.

Manhattan Borough President Gale Brewer has said she prefers that repairs be “limited to the nights and weekends option to minimize effects on daily commuters and businesses.”

But the RPA report recommends doing all the disruptive work at once to “spare riders more inconvenience.” Also, “it’s less costly to bundle these upgrades together than to spread them out over years,” according to the RPA.

Five Manhattan L train stations also need to be shut down, said the report, to permit “unimpeded 24/7 access by work crews.” The recommended improvements would also help make the Eighth Ave., Sixth Ave., First Ave. and Third Ave. stops in Manhattan ADA compliant and add additional access for people with disabilities.