Lane-By-Lane Modelling of Unequal Lane use and Flares at Roundabouts and Signalised Intersections: The SIDRA Solution

Abstract

This paper was prepared in response to two articles, "ARCADY Health Warning: Account for unequal lane usage or risk damaging the Public Purse!" by B. Chard, and "Modelling flares at traffic signal-controlled junctions" B.F. Simmonite and P. Moore. These articles address problems associated with the "approach" method of traffic modelling which lumps traffic in individual lanes of an intersection approach together. Chard demonstrates by means of case studies that "(the ARCADY model) can take no account of either unused or unequally used lanes or flared sections on roundabout entry approaches. Simmonite and Moore state that "the art of modelling (flared approaches) is difficult and, as such, often overlooked by practitioners". This paper discusses important aspects of the two articles from the perspective of the lane-by-lane method and short lane model used in aaSIDRA (SIDRA INTERSECTION) software for all types of intersection (signalised, roundabout, sign control). SIDRA computations are heavily based on estimating lane flows, modelling traffic in shared lanes including any lane blockages, establishing any de facto (effective) exclusive lanes, determining reduced short lane capacities and any excess flows from short lanes into adjacent lanes.