Optimal operation of displaced left-turn intersections: A lane-based approach

• Ten types of displaced left-turn intersections (DLT) are integrated in a unified framework.
• A generalized lane-based optimization model is developed for operation of DLT.
• Spatial and temporal parameters of DLT are optimized simultaneously.
• Extensive numerical analyses are conducted to reveal the effectiveness of the proposed method.
• Applicable domain of different DLT is identified and analyzed.

Displaced left-turn (DLT) intersections that resolve the conflict between left-turn and opposing-through movements at the pre-signal are probably the most extensively used innovative intersection designs. The DLT intersection concept can be extended to ten different types according to the location of the left-turn transition area, the number of DLT approaches, and the possible setting of the bypass right-turn lane. This paper presents a generalized lane-based optimization model for the integrated design of DLT intersection types, lane markings, the length of the displaced left-turn lane, and the signal timings. The optimization is formulated as a mixed-integer non-linear program. This program is further transformed to a series of mixed-integer linear programming problems that can be solved by the standard branch-and-bound technique. Results from extensive numerical analyses reveal the effectiveness of the proposed method, as well as the promising property of assisting transportation professionals in the proper selection of DLT intersection types, and the design of geometric layout and signal timings.