SACRAMENTO—For almost 29 years, California insurers have uttered the phrase “Proposition 103” like a curse.

The 1988 voter-approved initiative forced insurance companies to roll back home and auto rates by 20 percent and to obtain the approval of an elected commissioner before increasing them. It also required insurers to set car policy rates based primarily on three factors: a driver’s safety record, his or her years of experience behind the wheel and the number of miles driven annually.