For those making policy to ameliorate problems, there is a typical dilemma. Saving lives usually means spending a lot of money. Saving money can often mean losing or damaging lives—the current debate over health policy underscores that set of tradeoffs. Rarely do we find a policy option that both saves lives and saves money. But that option is here for this immense problem. It is called crisis intervention team training, or CIT, and it works—there’s data, and results, to prove it.

Miami-Dade County is a behemoth; it’s the seventh most populous county in the United States, with over 2.7 million people in 34 incorporated cities and towns. It also has the highest concentration of those with serious mental illnesses in the country: 9.1 percent of the general population, which translates to 192,000 adults and 55,000 children. Seventeen years ago, Miami-Dade experienced the same kind of violent encounters on a regular basis that we see reflected in the news today. There was, on average, one death a month stemming from interactions between police and residents with these illnesses, along with about 20,000 arrests and incarcerations each year.

Yet since 2010, the two largest police agencies, the City of Miami and Miami-Dade County police, have handled 71,628 mental health-related calls—and have made only 138 arrests. Miami-Dade taxpayers were on the hook for millions of dollars from wrongful-death lawsuits; today, fatal shootings are down almost 90 percent. More than 20 percent of those in county jails had serious mental illnesses, costing many millions to keep them there. Recently, the decline in arrests and incarcerations enabled the county to close a jail and save taxpayers $12 million a year.

What changed? A comprehensive program to structurally transform the way the community responded to people with mental illnesses (which Miami-Dade County Judge Steve Leifman, one of the authors of this piece, initiated). A key component was the CIT training of over 5,400 police officers in Miami-Dade, representing all 36 police departments, using a 40-hour program crafted initially in Memphis, Tennessee, in the late 1980s. To be sure, it was not easy. First, many police officers believe they know what they are doing and don’t think they need additional training. Second, it was a battle to convince police chiefs to take their cops off the beat for a week to take the course.

Aided by a grand-jury report investigating the criminalization of people with mental illnesses by the local state attorney, Katherine Fernandez Rundle, the program took off. Police dragged reluctantly into the program became believers—especially after they saw the results firsthand when they went back onto the streets. Most officers don’t seek confrontation; they prefer peaceful resolution of incidents or disputes. As Miami-Dade Police Director Juan Perez put it, “Our police department understands and believes that treatment over arrest for the mental-health population provides better, long-lasting results.”