Transit advocates slapped the NYPD with an “F” for failing to enforce bus lanes across the city on Tuesday — and their report claims cops are among the city’s biggest transit blockers.

The department’s “general culture of disrespect for bus lanes” leaves the MTA with little recourse against obstructing autos, the Bus Turnaround Coalition asserted in its report released Tuesday.

The MTA’s efforts “are negated by the number of squad cars and personal vehicles with NYPD parking placards that routinely obstruct bus lanes and bus stops,” according to the report.

Even though cops are handing out more bus lane violations in 2019, “the real breakthrough will come when police stop blocking bus lanes themselves and start cracking down on parking placard abuse that makes life harder for bus riders,” the report said.

New York City’s buses are the nation’s slowest and have hemorrhaged riders for nearly two decades. Experts say sluggish speeds are a major cause of the ridership slide.

Dedicated lanes let buses circumvent the city’s brutal gridlock — but they only work if cleared of obstructions.

“We’ve seen a lot of good things from [NYPD]. They’re definitely ramping up their ticketing,” TransitCenter staff analyst Ashley Pryce, who wrote the report, told The Post.

But, Pryce said, “Any cars, particularly NYPD cars, that are blocking bus lanes mean that but riders can’t get where they need to go quickly and efficiently.”

“How can they expect anyone else to respect bus lanes if they’re not?” she added.

The city and MTA have stepped up camera-based bus lane enforcement this year, after the state legislature eliminated the limit on the number of routes where such enforcement can exist.

Two bus routes — the M15 and B44 — were recently equipped with bus-mounted cameras. In the 10 days after cameras turned on, M15 cameras caught 1,500 bus lane violators.

The NYPD defended officers blocking lanes as an unfortunate side effect of police work.

“Due to the nature of police work, including responding to 911 calls, officers may temporarily place police vehicles in restricted areas in order to provide an emergency response,” Sgt. Jessica McRorie said in a statement.

“The use of parking placards by NYPD members is restricted and misuse of placards is prohibited,” McRorie said.