Chlewicki (2003) introduced two new designs developed by himself, the Synchronized Split-Phasing Intersection and the Diverging Diamond Interchange (DDI).The diverging diamond interchange developed from the concept of the synchronized split-phasing design. The designs take advantage of the benefits of split-phasing and signal synchronization to theoretically improve signal timing at heavy volume interchanges or heavy turning movements. Simulations were conducted to compare the delay of these new designs to other conventional designs. The idea behind the DDI was to use the crossing over movement on an interchange design. The conventional diamond interchange seemed to be the easiest design to create crossover movements for. The main goal was to better accommodate left turn movements and potentially eliminate a phase in the cycle for the signals. Figure 1 shows the layout of the diverging diamond interchange. The highway portion, shown in the northbound/southbound direction, does not change but the movements off the ramps change for left turns. Through and left turn traffic for the arterial road also maneuvers in a different manner from a conventional diamond interchange because the traffic crosses to the “wrong” side in between the ramps.
The biggest potential benefit for the DDI is the ability to combine phases in ways that cannot be done in other interchange designs. Ramp phases can be combined with a mainline through movement, and mainline left movements can be combined with though movement throughout the whole phase. Also coordination of the signals can be made between a ramp phase and a through phase without much difficulty and the reduction of a phase could benefit the signal timing. Also the diverging diamond interchange was found to have less conflict points than a conventional diamond interchange. The diverging diamond interchange was compared to a conventional diamond interchange, where the total delay for the conventional diamond was about three times as great as the diverging diamond, and the stop delay was over four times. The authors stated there seemed to be great potential for the DDI design but more research would be needed to be done to look into changes in traffic patterns and signal spacing, as well as a cost analysis.