SAN DIEGO—Some board members of the San Diego Association of Governments (SANDAG) on Dec. 3 are looking for alternatives—instead of charging county residents for every mile they drive—to fund the county’s regional transportation plan. The four-cents-per-mile road usage tax proposal—and two half-cent regional sales taxes proposed for 2022 and 2028—was envisioned as a way to help fund SANDAG’s long-term regional plan. This ambitious 30-year, $160 billion plan could include no-cost public transit and a 200-mile, $43 billion regional rail network. Some of the most powerful members of the SANDAG board, which weighs votes by a city’s population, said they were uncomfortable with the details of such a tax. “At this time, the local road usage charge as a replacement for the gas tax remains highly speculative, with very few details available about how it would work or be applied in a fair way,” said Encinitas Mayor Catherine Blakespear, chair of SANDAG’s Board of Directors. “I am concerned that the road usage …