The Double Roundabout interchange uses Roundabouts
instead of signal- or stop-control at Diamond interchange
ramp terminals. Intended benefits include reduced
delay for ramp traffic, a narrower bridge width,
and the elimination of signal coordination and progression
issues between the two ramp terminals.
The Roundabouts in the Double Roundabout design
can have two different shapes, either circular or
"raindrop". The use of true circular islands is desirable
when U-turns or access to other approach legs are
to be permitted. Raindrop-shaped central islands
eliminate direct U-turn movements (U-turns can be
made by circulating around both Roundabouts), but
reduce yielding conflicts for vehicles entering
the Roundabout from the ramps, thus improving the
capacity of the Roundabouts and reducing ramp delays
and queuing.