Highways in the Midwest faced lengthy delays because of snowy weather or crashes and authorities in parts of Indiana, Michigan, New York and Ohio urged motorists to avoid nonessential travel.The Federal Aviation Administration (FAA) imposed ground stops or delays for de-icing at a number of U.S. airports because of winter weather.Transportation Secretary Pete Buttigieg told CNN the U.S. aviation system "is operating under enormous strain" with two different storms and high winds affecting airports around the country.Another 10,400 U.S. flights were delayed on Friday - including more than 40% of those operated by American Airlines (AAL.O), United Airlines (UAL.O), Delta Air Lines (DAL.N) and Southwest Airlines (LUV.N) - after 11,300 flights were delayed Thursday.The FAA lifted a ground stop there due to snow and ice but late Friday delays were still averaging nearly three hours."