Jan 20 will be on a Tuesday, with the inauguration ceremony at noon. Daily commuter traffic in and out of DC is around 400-500K, so they will need to deal with six times normal commuter traffic.
They have scheduled overtime for all the mass-transit workers, and will be supplying rush-hour-level service from 4am to 7pm on the day. I don't think this will be enough.
DC will be much more of an insane zoo than usual.
Let us not underestimate the audacity factor.