Here’s another example of how James Vacca and Jessica Lappin, if they’re serious about street safety, targeted the wrong agency for a public scolding yesterday.

In September, DOT completed the installation of Manhattan’s first 20-mph “Slow Zone,” between Dyckman and W. 218th Streets west of Broadway, in Inwood. This Slow Zone was requested by my neighbors and approved by Community Board 12. Within its boundaries are two parks, several churches and schools, and at least one daycare center — and of course the homes of thousands of people who want to walk and bike their neighborhood without fear of being harmed by speeding motorists.

Before the Slow Zone was completed, the 34th Precinct, which covers all of Inwood and part of Washington Heights, had issued a total of 50 speeding citations in 2012. In the three months after the speed humps and Slow Zone markings went in, and the speed limit in Inwood west of Broadway was lowered to 20 mph, the precinct handed out two speeding tickets. In November and December, not one driver was cited for speeding by the officers of the 34th Precinct.

We have asked NYPD how many speeding tickets, if any, were issued on Inwood surface streets by the Highway Patrol in October, November, and December, but have yet to hear back.

Vacca has endorsed a 20 mph speed limit for all of New York City. He understands that speed kills. He is also surely aware of the proverbial three “E”s of traffic safety: education, engineering, and enforcement. While DOT has succeeded in educating the public on the concept — there are more applications than DOT can handle — and the engineering cues are impossible to miss, to achieve its full potential the Slow Zone program needs NYPD to provide enforcement. Under Ray Kelly, however, NYPD has demonstrated little to no interest in doing its part to help make streets safer, whether the task is enforcing speed limits or holding dangerous drivers accountable.

The fact is no city agency is doing more to reduce traffic deaths and injuries than NYC DOT. If anything, thanks to lax enforcement by police and electeds who prefer grandstanding to governing, NYPD and the City Council have made it more difficult for DOT to do its job.

If Vacca and Lappin have any doubts about which department has failed to hold up its end of the deal on matters of street safety, I have a Slow Zone to show them.