Displaced Left-Turn Intersection: A Two-Stage Model and Application Insight

To improve intersection performance by reducing left-turn conflicts, the displaced left-turn (DLT) intersection, including the continuous flow intersection (CFI) and parallel flow intersection (PFI), could serve as an at-grade solution. This study proposes a two-stage model for the optimal design of DLT intersections. At Stage 1, a mixed integer linear program (MILP) is formulated to jointly determine the reserve capacity, lane configuration and green ratio. At Stage 2, based on the output of Stage 1, we propose a linear program to coordinate the signal plans between the main intersection and four sub-intersections created for left-turn traffic. Numerical experiments examine the effect of traffic demand and left-turn proportions on DLT while comparing DLT with conventional intersections. Results show that CFI outperforms conventional intersections and PFI in most cases. Little difference exists on vehicular delay between CFI and PFI under the small/medium demand input, while the difference becomes more prominent as left-turn traffic demand increases.