Characterization of Trajectories Adopted at Roundabout Crossings

Abstract

Generally roundabouts that offer multiple circulation lanes are associated with lower performance levels when compared with single lane roundabouts. The increase in the number of lanes allows drivers to have greater liberty in their behaviour which as a result generates more conflicts. Therefore the direct observation and analyses of driver behaviour is justified namely in what regards to trajectories during the approach and crossing of the roundabout. In order to achieve a successful roundabout design it is important to use solutions that induce natural and instinctive behaviours in accordance to driver expectations without resulting in conflicts with vehicles that may be using in adjacent lanes. This study intends to improve the knowledge of driver behaviour on a roundabout namely on the trajectoriesadopted. The work is based in a real data base of 2100 trajectories made by 14 drivers. The data was collected in free flow conditions in 20 circuits in roundabouts in a 2x2 lane cross section environment. The need to have acceptable levels of reliability on the data collected and in order to evaluate driver actions when controlling the vehicle lead to the use of an instrumented vehicle. This vehicle could accurately measure driver use of the vehicle commands and its dynamic response. The data collection methodology is explained as well as the graphic and mathematical representation process and the general characterization of drivers trajectories using a set of dispersion indicators measured in critical sections of the circuit. In complement the basic principals that influence each driver and the way they are valued by each driver are explored. It was possible to conclude that driver behaviour is dictated by different valorisations of the "temptation" to minimize driving discomfort and the "obligation" to respect horizontal road markings. This principle results in the adoption by each driver of trajectories that sometimes tend to approach the minimum discomfort trajectory (the most direct ones based on the physical restraints) and as a consequence in searching more direct trajectories even if this goes againsthorizontal road markings. One of the situations is the adoption of directtrajectories by drivers using the left lane when entering the roundabout and exiting it on the right lane in complete disregard of horizontal road markings. The other situation is associated with drivers that choose the right lane to enter the roundabout and cross directly the circulatory zone invading the left lane. For the covering abstract see ITRD E135582.