Increasing signalized intersection capacity with flexible lane design

Limited road space presents major challenges in enhancing the operational efficiency of isolated intersections. Lane layout optimization emerges as a critical strategy for harnessing the potential capacity within these constrained spaces. Current methods primarily focus on optimizing lane allocation based on a fixed number of lanes with standard widths, proving ineffective in addressing the growing trend of vehicle miniaturization. This study introduces an innovative lane layout design approach that simultaneously determines the optimal lane number, width, type, allocation, and signal settings, thereby increasing the capacity of isolated intersections. The proposed method introduces three distinct lane types: conventional width lane (CWL), special width approach lane (SWAL), and dedicated passenger car lane (DPCL) to fully utilize available road resources. The interdependencies among CWL, SWAL, and DPCL are initially clarified, followed by quantifying the adjusted saturation flow rate for each lane type. Subsequently, a refined lane-based method is proposed to determine the optimal lane layout and signal timing, with road width as the primary input parameter. The optimization model is formulated as a mixed-integer quadratic programming problem, which can be solved using the standard branch-and-bound technique. Comprehensive numerical analyses demonstrate that the integration of DPCL and SWAL leads to an average capacity increase of 12.51 % at intersections. Furthermore, utilizing road width as the input parameter significantly enhances optimization flexibility, resulting in greater capacity improvements compared to relying solely on the number of lanes. Importantly, this lane layout design method proves versatile and applicable to intersections with diverse road widths, varying heavy vehicle ratios and traffic fluctuations.