Transportation to and from the Boston area is virtually shut down Friday morning, with the exception of airplanes, which continue to take off and land at Logan International Airport. Amtrak has stopped trains about an hour south of the city in Providence, R.I. The Massachusetts Bay Transportation Authority, which operates commuter trains into Boston as well as the city’s subway – called the T – and the city’s buses suspended all operations. JetBlue, the largest airline in Boston, is allowing anybody scheduled to fly to or from Boston to change their ticket for free. Megabus has canceled at least 18 buses between Boston and New York, New Haven, Conn., Hartford, Conn., Burlington, Vt. and Philadelphia.