From Rt 50 down 301 from Bowie at last count there were 52 traffic lights, several with cameras, to the bridge into VA which has on going construction. Don't bother just go on into the DC beltway I-95 495. I don't know if the new WW drawbridge has ever been opened so I wouldn't worry about that. I always go straight down I-95 through Richmond but with the trailer might be easier to take the by pass. For some reason traffic is always slow in SC and the road its self is awful. Depending where you are going offers some options in FL, if going to the East coast, Orlando stay on I-95 right through Jacksonville. If going down the other side take exit 129, FL route A1A over to Callahan and hit 301 which takes you right down through the center to just North of Ocala where you can get on I-75. You even have choices after that. Trick to DC Baltimore area is timing. You come through there at the wrong time you are in for a long day. I just made this trip 6 weeks ago on the west side and last year to West Palm Beach. Be safe