Characterization of Trajectories Adopted at Roundabout Crossings



Characterization of Trajectories Adopted at Roundabout Crossings

Authors

Ana Bastos Silva, Álvaro Jorge da Maia Seco, University of Coimbra, PT; João Pedro Cruz da Silva, Polytechnic Institute of Leiria, PT

Description

The use of roundabouts is normally associated with low emissions and accident levels as well as good levels of service.
This study intends to improve the knowledge of driver behaviour on a roundabout namely on the trajectories adopted.

Abstract

The use of roundabouts in urban and rural areas is normally associated with low emissions and accident levels as well as good levels of service. It is also highly adaptable to demand variations. These benefits have justified their adoption by several countries in conflict management in new intersections and also in upgrading existing intersections.
However the international experience has shown that the performance level of a roundabout is highly dependent of its general characteristics and in particular in its ability to influence driver behaviour.
Several countries have defended that although a roundabout (when correctly designed) is an efficient physical speed control measure that result in homogeneous behaviours some functioning problems subsist related with driver behaviour that become worse in severity and frequency when the entrance design is less restrictive and more entry and circulation lanes are provided.
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 trajectories adopted.
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 against horizontal road markings.
One of the situations is the adoption of direct trajectories 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

Publisher

Association for European Transport