The hov lane starts right before the 14th street bridge entering Virginia. If you got up to 3 digits before crossing the bridge, that would be quite impressive, heh. VA cops regularly patrol their side of 395 and the HOV lane in that area now, so it would be hard to get away with it these days.
I got a ticket for 79 in a 55 in that same area about 6 years ago. The fine was nearly $400 IIRC. I haven't done that again since, heh.