Ringing the Bay with medium- to high-density housing is the best way to save on mounting infrastructure costs and reduce commuter congestion as the region's population grows, according to a plan being shopped around by regional transportation experts. [...] What that development might look like ranges from skyscrapers in metropolitan downtowns to two- to five-story buildings along the Peninsula, according to officials. "There won't be a one-size-fits-all solution, so the type of growth that would fit in San Francisco or Oakland wouldn't necessarily make sense in less urban areas," said Janet McBride, planning director for the Association of Bay Area Governments."