A majority of the San Diego County Board of Supervisors rejected key parts of the San Diego Association of Governments’ new multibillion-dollar plan for regional transportation. The divided board voted 3-2 Tuesday for the county to oppose much of the new proposal, which would dramatically shift regional transportation priorities toward expanding public transit and away from building highways and roads. Supervisors Dianne Jacob, Jim Desmond and Kristin Gaspar voted for the measure, while Supervisors Greg Cox and Nathan Fletcher voted in opposition.