BTU, making it the seventh-lowest state in terms of consumption of energy per capita, and 31 percent of that energy came from natural gas. In 2014 and 2015, Massachusetts was ranked as the most energy efficient state the United States while Boston is the most efficient city, but it had the fourth-highest average residential retail electricity prices of any state. In 2018, renewable energy was about 7.2 percent of total energy consumed in the state, ranking 34th. Transportation Massachusetts has 10 regional metropolitan planning organizations and three non-metropolitan planning organizations covering the remainder of the state; statewide planning is handled by the Massachusetts Department of Transportation. Transportation is the single largest source of greenhouse gas emissions by economic sector in Massachusetts. Regional public transportation The Massachusetts Bay Transportation Authority (MBTA), also known as "TheT", operates public transportation in the form of subway, bus, and ferry systems in the Metro Boston area. Fifteen other regional transit authorities provide public transportation in the form of bus services in the rest of the state. Four heritage railways are also in operation: The Cape Cod Central Railroad, operating from Hyannis to Buzzard's Bay The Berkshire Scenic Railway, operating from Lee to Great Barrington Edaville Railroad in Carver The Lowell National Historical Park Trolley Line in Lowell Long-distance rail and bus Amtrak operates several inter-city rail lines connecting Massachusetts. Boston's South Station serves as the terminus for three lines, namely the high-speed Acela Express, which links to cities such as Providence, New Haven, New York City, and eventually Washington DC; the Northeast Regional, which follows the same route but includes many more stops, and also continues further south to Newport News in Virginia; and the Lake Shore Limited, which runs westward to Worcester, Springfield, and eventually Chicago. Boston's other major station, North Station, serves as the southern terminus for Amtrak's Downeaster, which connects to Portland and Brunswick in Maine. Outside of Boston, Amtrak connects several cities across Massachusetts, along the aforementioned Acela, Northeast Regional, Lake Shore Limited, and Downeaster lines, as well as other routes in central and western Massachusetts. The Hartford Line connects Springfield to New Haven, operated in conjunction with the Connecticut Department of Transportation, and the Valley Flyer runs a similar route but continues further north to Greenfield. Several stations in western Massachusetts are also served by the Vermonter, which connects St. Albans, Vermont to Washington DC. Amtrak carries more passengers between