A sinkhole was discovered under the railroad track eastbound lane of the grade crossing in Bethel.  Greenwood Avenue in Bethel is closed between Library Place and Blackman Avenue while Metro North makes repairs to the railroad crossing. Drivers should use South Street as a detour.  First Selectman Matt Knickerbocker says this will be an extended closure, likely through the weekend.  The repair requires the removal and replacement of about 30 yards of track, ties and grade crossing platforms.  Metro North is running substitute bus service between Danbury and Redding, with train service running between Redding and South Norwalk as normal.