Across the five boroughs, drivers routinely block bus lanes and bike lanes, slowing down transit riders and putting cyclists at risk. The worst offenders are police officers and placard holders who undermine the city’s efforts to improve conditions for transit and cycling on the streets.

Mayor de Blasio is their boss, but on his weekly appearance fielding calls on the Brian Lehrer show, he deflected questions from a listener who asked what the mayor intends to do to about it.

The caller, Alex Bell, is a computer scientist whose work quantifying the obstruction of bike lanes and bus stops in Harlem was profiled by the Times yesterday. Bell found that one bus stop on St. Nicholas Avenue was blocked 57 percent of the time, while nearby bike lanes were obstructed 40 percent of the time.

Bell mentioned his findings before putting his question to the mayor. “With bus service at an all-time low and falling, bicyclists and pedestrians dying in the streets, how are you going to fix the problem of enforcement?” he asked. “Because the laws are there, the NYPD is unwilling and unable to enforce traffic laws. What is your solution? And don’t tell me it’s a state issue.”

De Blasio became very defensive, accusing Bell of having “an ideological worldview” that doesn’t reflect the “facts.” MTA buses aren’t operated by the city, he noted, and NYPD had to prioritize other moving violations over bike and bus lane violators.

Pressed by Lehrer on whether he thought Hall had “an ideological axe to grind,” de Blasio said he thought he did. Not for the first time, the mayor went on to excuse bike lane blockers.

“I think it is obviously, there’s always the question of where we put our officers to have the maximum impact,” he said. “If someone is blocking, for example, a bike lane for 30 seconds while they take out their groceries or they let their kid off, I don’t think they should get a ticket for that. If someone leaves their car for any meaningful amount of time, they should be penalized.”

It was one of de Blasio’s more clueless performances. He displayed no awareness of the pervasiveness of bus lane and bike lane obstruction, why it undermines his own transportation initiatives, or the role of agencies under his control — namely NYPD — in perpetuating the problem. Police officers don’t just fail to enforce bus lanes and bike lanes, they are the worst violators.

As mayor, de Blasio oversees the police who obstruct lanes that should be clear, the placard system that leads to rampant violations of bus lanes and bike lanes without consequence, the stipulated fine program that reduces incentives for delivery companies to observe parking rules, and the curbside regulations and meter prices that clog streets with illegal parking.

These are all policy levers within de Blasio’s power to address, they’re not up to the MTA or Albany. Without an engaged mayor who understands that, New York’s relentless traffic dysfunction will continue.