Split sentencing, in which a felon serves a portion of his time in jail and another portion in the community but under supervision, shows promise.

Criminal defendants convicted of felonies in California used to be sentenced to state prison. Most, after serving 50% of their terms, were released on parole and returned to their communities. And of them, most ended up back in prison, either because they committed new crimes or because they were caught violating parole. California was good at running felons through a revolving door and very bad at guiding their safe return to society: getting the addicted off drugs, getting treatment for the mentally ill, getting those with antisocial and criminal mind-sets into structured, supervised programs with reliable records of reforming those former inmates who were amenable to reform.

The state had a Department of Corrections and Rehabilitation, but in most cases it neither corrected nor rehabilitated. It kept criminals incapacitated, but when they returned to their neighborhoods, they were at least as dangerous as when they were sent away.

Today, defendants convicted of felonies defined by law as violent, serious or sexual continue to go to state prison; and despite widespread public misunderstanding and assertions to the contrary by officials who ought to know better, defendants convicted of lesser felonies also go to state prison if they have rap sheets that include past violent, serious or sexual offenses.

But since October 2011, newly convicted "non-non-non" felons — those whose offenses are not violent, serious or sexual — with no current or previous record of serious convictions go to county jail. Just like their counterparts in state prison, they will serve their time, get out and return to their communities.

And then what? The addicted and the mentally ill will most likely remain untreated; they and other inmates badly in need of life skills, anger management counseling or similar programs will leave jail at complete liberty, with an unstructured reentry into society. Their prospects for success — shunning trouble, getting work, leading productive, crime-free lives, leaving their neighbors safe — will be about the same as those of felons returning from state prison: not good.

Evidence has shown, time and again, that the outcomes are better for inmates who begin programs in jail — and who then return to society under supervision while continuing mandatory treatment and education. There are three choices for dealing with inmates, and three well-documented outcomes: no treatment or education in or out of jail, and a poor chance at success; compelled treatment and education in jail, and slightly better chances; and mandatory treatment in jail followed by mandatory treatment and monitoring, for a period of time, on return to society, with much improved prospects of breaking the cycle of offending, being locked up, returning to the streets and offending again. And keep in mind: The beneficiaries of these programs are not just the offenders but also those who are victimized by them.

AB 109, the criminal justice realignment laws adopted in 2011 that gave counties new responsibilities over low-level felons, also proposed a reinvention of the reentry process to deal with criminal recidivism. Defendants could receive what is known as a "split sentence," with a portion of the time to be served in jail and another portion to be served in the community, under supervision by probation officers who would monitor mandatory participation in rehabilitation and other programs. The period served under supervision in the community, after release from jail, is known as a "tail."

In keeping with the spirit of realignment, which gives counties maximum flexibility to experiment, compile data, compare notes and adjust as necessary, AB 109 doesn't mandate split sentencing. Nor does it compel counties to abide by any formula or guideline in determining how much it can spend on programming, or what kind of programs to offer. Counties can decide whether to spend more of their realignment funding on incarceration or reentry.

Some counties — especially those already geared toward community-based corrections for their misdemeanor defendants — have embraced split sentencing. In Contra Costa County, for example, 90% of the AB 109 felony sentences are split. Other counties and their trial courts are also turning to split sentencing, pairing the post-incarceration tail with innovative and proven programs that reintroduce felons to their neighborhoods with carefully tailored treatment and scrutiny. Because more time is served under community supervision, jail cells are freed up for the most dangerous offenders.

So how tightly is the state's largest jurisdiction, Los Angeles County, embracing the opportunities presented by split sentencing? This county is bottom of the barrel, with a supervised tail in only 4% of sentences.