Police have woken up more than 100,000 sleeping straphangers on the subway this year — as part of ongoing efforts to deter crime in the city’s underground transit system, the NYPD’s transit chief revealed Monday.

The tactic helps ensure that riders “protect themselves by them being aware of their surroundings,” Transit Chief Ed Delatorre told an MTA board committee meeting.

Those roused by officers are given “crime prevention cards that highlight the risks of inattention and encourage riders to be mindful of their property,” an NYPD spokesperson later added.

The program is referred to by some NYPD insiders as “shake and wake.”

When riders are awake, they are less vulnerable to attack — which prevents crimes before they happen, a high-ranking police source told The Post.

“It’s imperative that you wake people up,” the source said.

“[Criminals] know they’re going to find some person who’s asleep. They walk up, watch them for a couple minutes cut their pants pocket or their purse strap. You wake up during that and they’ll slash you in your face or your arm.”

The source expressed shock at transit riders who snooze through their commutes in the first place — particularly given this year’s spike in serious crimes like sexual assault and robbery.

“Why would you go into a subterranean forest and think it’s OK to go to sleep down there?” the source said. “You get robbed because you’re asleep and now it’s our job to find out who did it to you?”