With the city’s progressive establishment firmly behind the drive to close the Rikers Island jail, Mayor Bill de Blasio’s plan to build four new borough jails to replace it moved ahead Tuesday.

Since the mayor controls seven of the 12 votes, the city Planning Commission’s OK of the land-use plan was a given. And the raucous protesters were even more radical, chanting, “No new jails! Close Rikers now!”

The City Council has 50 days to amend or kill the plan, but that will only mean favor-trading to buy off members whose constituents fear a new jail in their neighborhood.

In fact, the rush is on to get as much built as possible before de Blasio leaves office, though the plan doesn’t call for Rikers to close before 2026.

This would leave the city with just 4,600 jail beds and no easy way to handle a serious spike in crime. Nor is that the only safety concern: As the city reduces the jail population to the hardest of the hard core, more pretty tough characters are walking the streets — and jail violence is on the rise, putting correction officers at greater risk.

Having a Plan B in place for when things go wrong sure would be nice.