Do the roundabouts usually only have one lane? The circles in DC usually have three lanes. The usual practice is for traffic that is going a longer way around the circle to get into the inside lane and traffic that is getting on and off to use the outside lane. I guess the middle lane is a transitional lane. With the circles, there are usually at least six and sometimes eight possible turn-offs because the circles occur where two roads going at right angles to each other intersect with an avenue or two, which usually run diagonally to the other roads.

DC is on a grid system with all of the main roads having either a letter name (going east/west) or a number name (going north/south). The exception to this rule is the avenues which go pretty much wherever they want, but mostly diagonally in relation to the other streets. I think the circles only occur where numbered and lettered streets intersect with avenues.