6:27 p.m. Update:

Red Line problems continue. Trains heading to Shady Grove are experiencing delays due to a train malfunction at Dupont Circle.

6:09 p.m. Update:

The single-tracking has cleared, though delays are continuing in both directions. Transit police report that the person who appeared to be suffering a heart attack is being taken to an area hospital.

6 p.m. Update:

It appears the sick customer suffered a heart attack, according to the Metro Transit Police:

Original Post:

Red Line trains are sharing a single-track between Judiciary Square and Union Station due to a sick rider at Union Station, creating major delays in both directions.