When a large organization in Los Angeles County suddenly faces a new and possibly existential safety — and perception of safety — problem, the urge for its leaders to create a security solution of their own is often the first response.

And very often — most of the time — such a notion is a wrongheaded, wasteful one indeed.

Los Angeles Metro knows that, post-pandemic, one of the reasons ridership has been hard to lure back is because of the preponderance of unhoused, drug-using riders on its trains and buses.

The upwardly mobile, middle-class CPA in Azusa does not want to start her day riding to work in Chatsworth accompanied by dozing junkies.

That’s why Metro in recent months began putting uniformed Ambassadors in some of its cars, helpful types whose very presence, it is hoped, will make riders feel safer.

But the Ambassadors are neither armed nor trained law-enforcement professionals, and there is a feeling more policing is necessary.

While that may be true, Sheriff Robert Luna is correct to warn, as he did this month at a meeting of Metro’s Public Safety Advisory Committee, against Metro creating a new police force of its own.

In an eight-page letter sent to Metro in October and recently uncovered, Luna said a Metro plan announced in June “severely underestimated the costs of starting and maintaining an in-house police department,” as our staff writer Steve Scauzillo reports.

Currently, Metro contracts with the sheriff and with the Los Angeles and Long Beach police departments as well for security. The Metro study claims it could create and run an internal department with 290 field officers for $134.5 million annually, cheaper than the $173 million a year it currently pays.

Nonsense, says the sheriff. The study doesn’t account for start-up costs, for pensions, for facilities, for liability costs. His analysis shows the idea would cost $433 million more over five years than the status quo.

There’s a reason 42 of the county’s 88 cities contract with the sheriff for law enforcement: efficiency.

We realize the LASD is not perfect. If Metro needs more tailoring in its contract, then press for it. But don’t try to reinvent the transit wheel.