The San Diego Board of Supervisors will consider on Tuesday whether or not to support a new multi-billion dollar plan by the San Diego Association of Governments that would dramatically shift that group’s regional transportation plan toward prioritizing public transit expansion over building highways and roads. The proposal, which SANDAG unveiled Friday at a special meeting, would better position the region to meet state mandates related to greenhouse gas emissions and would add hundreds of miles of high-speed transit lines throughout the county, as far east as Poway and as far north as Oceanside, supporters say.