Thomas Boccaleoni, 47, pleaded no contest in Sonoma County Superior Court to forcible anal or genital penetration on Nov. 18, 2008, attempted sexual battery on Jan. 6, 2009, and assault with intent to commit rape on April 18, 2009.
Boccaleoni will be sentenced to 15 years and 8 months in prison on Nov. 7 as part of his plea agreement, under which the other seven charges against him will be dropped.
His trial was scheduled for Nov. 2. He had faced 28 years in prison if convicted of all 10 charges.
According to testimony at his preliminary hearing, on two occasions, Boccaleoni flashed the headlights of his car at vehicles with female drivers. Each time, when the driver pulled over, he told her to call 911 because there had been a motorcycle accident. He would then sexually assault the women.
In the third incident, when the female driver pulled over, Boccaleoni told her that her car was leaking fluid and might catch fire, according to the preliminary hearing testimony.
He then wedged himself between her car door and fondled her from her thigh to her neck, according to the testimony.
Boccaleoni Thursday morning admitted having a prior strike for committing a residential burglary in San Francisco on Dec. 15, 2005. That admission doubled his sentence in the Sonoma County roadside assaults case to 15 years and eight months.
Defense attorney Andy Martinez said Boccaleoni agreed to plead no contest because he didn't want any of the women to have to testify.
There also was an issue about the availability of DNA evidence against Boccaleoni throughout the legal proceedings, Martinez said. The defense alleged that some of the evidence had been destroyed at a Department of Justice lab in the East Bay.
Boccaleoni will have to register as a sex offender and will be on parole for 10 years after is released from prison, Martinez said.
He has been in jail since his arrest on April 28, 2009, and will receive some credit for time served.