I appreciate the information very much.  I'm guessing that the 2 Dowling roundabouts are too small for the amount of traffic they carry.  (Just "eyeballing" it, I don't believe they are over 150' in diameter.)  I wonder if studies have been made that consider the speed of vehicles approaching a roundabout.  Vehicles on the exit ramps are rapidly decelerating, but Dowling traffic tends to move more quickly.

I realize this has nothing to do with the accident, but I've wondered why the roundabouts seem to be more of a nuisance ... it could be a design fault that makes me nervous about using them.  I notice other commenters have similar reactions.  I try to avoid those roundabouts, especially during rush hour.