(Benjamin C. Tankersley/The Washington Post.)

States may finally be getting a handle on a problem that’s been festering for years.

For decades, state prisons have added inmates at a rate three times faster than the nation has added people. By 2012, they were spending more than $50 billion annually on prisons. But two years earlier, a federal program was created to nudge downward the trajectory of costs and population growth. It offered money to analyze and address the problem and a new report shows that it may help states save as much as $4.6 billion and, in some cases, dramatically shrink prison populations.

If projections fully materialize, the program, called the Justice Reinvestment Initiative, “will represent a massive return on the federal and private resources invested,” according to the report from the Urban Institute. It’s of course too early to say for sure whether the estimates will come true, but if they do, it would amount to a 270-fold return on the federal government’s investment of $17 million.

The report focuses on 17 states. In that group, corrections accounted for anywhere from 4 percent to 12 percent of spending, with most in the 7 or 8 percent range. The program offered a framework to follow—one that starts by convening a bipartisan working group, preferably with members from various branches of government. States could get also grants for training, data management, program development and administrative assistance.

Some themes emerged from their assessments:

• Probationers and parolees were often returning to jail, sometimes for committing new crimes but often for technical violations, such as alcohol and drug infractions. In Missouri, those violations accounted for more than 80 percent of probation revocations to prison between 1995 and 2010. So states began investing in ways to minimize those infractions, such as increased funding for mental health and substance abuse services.

• States also found sentencing policies were driving up incarceration rates. Trends in the way judicial decisions were made, along with limited probation or diversion programs, made jail the preferred option when alternatives could have been implemented. So some states changed sentencing guidelines, removing or weakening mandatory minimum requirements for first-time offenders involving minor crimes, for example.

• Other themes affecting cost and population included: poor supervision and support programs and parole processing delays or denials. States responded by freeing up resources for support programs and reforming those parole systems.

The reforms are estimated to shrink state prison populations by anywhere between 0.6 percent in some states to as much as 19 percent. Hawaii, for example, expects to shrink its population by about 800 inmates between 2012 and 2018, amounting to a 14 percent reduction. In several states, such as Arkansas, the prison population is still projected to grow, but more slowly than without the program’s reforms.

Prison reform savings. (Urban Institute.)

Implementing the various reforms is also expected to save $4.6 billion over 11 years by reducing operating and construction costs. Arkansas is projected to save $875 million over 11 years, more than any other state in the report. North Carolina and Ohio are projected to save more than $500 million over six and four years, respectively.

There’s no guarantee the projections will become reality. Even the authors note that the findings should be taken with caution. “Data are still limited—for most states, it is too early in the implementation process to offer definitive conclusions,” the authors warn.

But if states see cost and population reductions anywhere near those huge projections, it would still represent a sizable return on the federal government’s investment.