Lane Utilization at Two-Lane Arterial Approaches to Double Crossover Diamond Interchanges

Double crossover diamond (DCD) interchanges, also known as diverging diamond interchanges, are popular and promising alternative interchanges that are increasingly being implemented nationwide. One unique feature of a DCD interchange is that through movements on the arterial road have to cross each other twice to complete their movements, while enabling left-turn movements from the arterial to the freeway to proceed without stopping at the downstream intersection. Consequently, interchanges with heavy left-turn movements are good candidates for DCD implementation. This unique feature of a DCD interchange means that there is a need to research lane utilization at the upstream approach intersection of DCD interchanges, as the lane use could be unbalanced. This unbalanced lane utilization could have a significant effect on operations at the first crossover and the interchange as a whole. This study examined lane utilization factors provided in the Highway Capacity Manual 2010 (HCM) for conventional diamond interchanges and found that they are not generally applicable to DCD interchanges. The study then proposed a lane utilization model calibrated with field data obtained at three DCD sites. The new model fit observed conditions at the DCD sites better than previously developed HCM factors. The model was then validated with three additional DCD interchanges, and validation results confirmed that the new model adequately predicted DCD lane utilization. The authors recommend that DCD interchange designers and analysts use the new model where it is applicable but also that more research be conducted to find lane utilization factors for other DCD configurations.