As The Post reports today, City Councilman Mark Gjonaj (D-Bronx) is prepping one Plan B in case Albany doesn’t renew the city’s school-zone speed-camera authority before classes start up again in September.

Fair enough — and we expect Mayor de Blasio has the NYPD and city Department of Transportation working on their own backup plans, even if City Hall doesn’t want to go public on it yet, lest it take the pressure off.

To recap: As The Post found last week, drivers are already zipping through school zones at perilous speeds, now that nearly all the cameras have gone dark.

We’ve warned that Senate Majority Leader John Flanagan could have blood on his hands if the Senate refuses to renew the city’s camera powers. But while Flanagan says he’s willing to cut a deal, he won’t OK the Assembly-passed bill to expand the program — and any actual agreement seems elusive.

Gjonaj’s idea has some merit: If the cameras don’t get restored, put up “radar signs” displaying drivers’ speeds — a cheap solution that could be rolled out at every school, not just the 120 where cameras had been active.

But City Hall can plainly do better — assigning police officers to high-risk areas, say, or having DOT install speed bumps.

Again, we don’t blame the mayor for not going public with any such plans yet. But with young lives at stake, drawing up a Plan B (and C and D) is also a moral duty.