Rebecca Lynn Haley, author of the study, defines the concept:
"Superstreets, also known as the restricted crossing u-turn (RCUT) by the Federal Highway Administration (FHWA), works by redirecting the side street left turn and through movements to a downstream, one-way median opening. Left turns from the major road can be accommodated by a u-turn maneuver after the intersection or by a left turn crossover at the main intersection."
Randal O'Toole concludes, from reading the report, that "...this greatly reduces both the time required for traffic signals to cycle and the number of conflict points between the two streets."
Diagrams of the traffic flow are available at The Antiplanner.