Re: Never trust a 'Merkin to build a roundabout.
Stupid Americans... Oh, wait... Did *WE* design this rotary with the traffic lights...?
As to the one that you showed -- Dupont Circle in Washington, D.C.; you can blame the French for that! Pierre Charles L'Enfant designed it in a grid, with diagonal streets radiating from large open squares spaced around the city. Which worked passably well for horses and carriages, but not so well for lots and LOTS of cars. Rotaries were the only real answer. And with lots of cars, and lots of pedestrians wanting to use the greenspaces in the middle of those areas, yeah... Short of constructing pedestrian over- or under-passes to go from the outside of the rotary to the park in the middle, stoplights at pedestrian crossings were really the best solution in a high-traffic area like that.
Specifically regarding Dupont Circle: Given the limitations imposed by L'Enfant's original street layout, there are only two streets on which you can unerringly pass through the intersection: Massachusetts and Connecticut Avenues. Mass. Ave. (The one that runs from 10 o'clock to 2 o'clock) uses the inner ring of the rotary.You can only ENTER the inner ring FROM Massachusetts Ave., and you can only EXIT it ONTO Massachusetts Ave., so it's not like you don't know where you're coming out -- you're coming out on the same street that you started on, going in the same direction, just on the the other side of the Circle. While one COULD enter from one of the other streets and veer into the inner ring at one of the Mass. Ave. entrances, you'd pretty much have to ACTIVELY turn into it -- the "bump-outs" to the outer ring at the Mass. Ave. exits and the divider between the two are fairly obvious guides. With Connecticut Ave. (The next street clockwise from Mass. Ave.), you can either ENTER the rotary, or -- if you simply want to continue down Connecticut -- pass UNDER it and come out on the other side, staying on Connecticut the whole time. Considering that L'Enfant's plan put FIVE major thoroughfares crossing in that square, it actually seems a rather elegant solution.