Superstreets

"A "superstreet" is a roadway where the signalized intersections have been modified to eliminate left turns and straight-through traffic on the cross street. Doing this reduces the number of traffic signal phases required to move traffic through the intersection thereby allowing for longer green times on the major roadway and thus reducing congestion caused by the signals."

They are a little complicated but are much cheaper than overpasses, and allow much more traffic than regular intersections.