The shared use of a single traffic lane by through and left-turn movements is one of the more complex operations that can occur at signalised intersections. A closed-form solution for evaluating the effect of shared lane use is described in the highway capacity manual (HCM). This paper investigates the methodology of the HCM shared lane analysis. It also extends that methodology to recognise the operational interdependence of saturation flow rate and lane use on opposing approaches. This extension is in the form of an iterative modification wherein the saturation flow rate and lane use on opposing approaches are incrementally updated. Using the modified methodology, several investigations were undertaken to determine the behaviour of shared lane operations. These investigations included comparing the modified methodology with the original HCM methodology; studying convergence trends; evaluating the effects of various timing and volume conditions; isolating a maximum volume threshold; and identifying the shared versus de facto left-turn lane regime. As a result of this examination, it was found that the HCM methodology consistently estimated slightly lower saturation flow rates than the final flow rate converged upon. A major outcome of the sensitivity analysis and evaluation study was a graphical technique for estimating the operational nature of a shared traffic lane.
Samenvatting