TAUNTON — State transportation officials are planning a public meeting to discuss ongoing efforts to develop a South Coast commuter rail line from Boston to New Bedford and Fall River.The meeting is scheduled to start at 6:30 p.m. Monday at Martin Middle School in Taunton.The Massachusetts Department of Transportation last month filed a draft supplemental environmental impact report for the project.The report describes MassDOT's approach to providing the new commuter rail service by taking advantage of existing active freight rail lines.