A number of states have used ballot initiatives for some measures of criminal justice reform:

Arizona

In 2002, the voters passed Proposition 302 that expanded current law so that a person who is convicted for the first time of personal possession or use of drug paraphernalia is eligible for probation and drug treatment and is not subject to incarceration.

California

In Proposition 47, which was approved by the voters in 2014, a variety of crimes were redefined down.  According to Ballotpedia:

The measure required misdemeanor sentencing instead of felony for the following crimes:

  • Shoplifting, where the value of property stolen does not exceed $950
  • Grand theft, where the value of the stolen property does not exceed $950
  • Receiving stolen property, where the value of the property does not exceed $950
  • Forgery, where the value of forged check, bond or bill does not exceed $950
  • Fraud, where the value of the fraudulent check, draft or order does not exceed $950
  • Writing a bad check, where the value of the check does not exceed $950
  • Personal use of most illegal drugs

    In January 2015, it was announced that as many as 1 million Californians could be eligible to change past felony convictions on their records under Proposition 47.New Jersey

    This state has recently reformed its bail system.  In 2014, a referendum was passed to completely restructure the system.  According to the Drug Policy Alliance:

    The legislation implements wide-ranging reforms including non-monetary release options for low-risk individuals; a system under which pretrial release decisions are based on risk rather than resources; the use of risk assessments for suspects enabling courts to make individualized determinations of what conditions of release are appropriate; establishment of a pretrial services unit within the court system that will provide appropriate levels of monitoring and counseling for those awaiting trial.