Use of Decision Assistance Curves in Advanced Warrant Analysis for Indirect Left-Turn Intersections

Abstract

This paper develops decision assistance curves (DACs) to compare delay-based performance measures for three indirect left-turn (ILT) intersections—median U-turn, continuous-flow intersection, and jughandle—relative to a conventional signalized intersection. The DACs consist of two graphical tools: (a) a DAC classifier and (b) two sets of DAC contours. DAC classifier plots are used to select the intersection type that produces the minimum system average delay for a specified main and cross-street volume configuration. DAC contour plots are used to estimate the system average delay difference between a chosen ILT and a conventional signalized intersection and to estimate the increase in average delay compared with a conventional signalized intersection for the movement most negatively affected. These tools can be used by planners, engineers, or other decision makers to identify visually the intersection type that provides the least average system delay under given volume conditions and estimated trade-offs for specific intersection types. The conventional signalized intersection, with protected left turns, was never optimal under studied scenarios. This finding implies that, for all the studied conditions, at least one ILT or permitted left-turn alternative produces lower delay than the conventional signalized intersection.