AROUND - Improving Capacity And Emission Models of Roundabouts

Publications

Driver Behavior Characterization in Roundabout Crossings

Publication . Silva, Ana Bastos; Santos, Sílvia; Vasconcelos, Luís; Seco, Álvaro; Silva, João Pedro

Roundabouts are widely accepted for their safety, capacity and environmental advantages. Although it can be easily recognized that the driver behavior is mostly related with the roundabout geometry. This paper presents a detailed characterization of the driver behavior while crossing three consecutive double-lane roundabouts in an arterial road. Driver behavior was described in three main levels: i) speed profiles; ii) lateral acceleration profiles; iii) roundabout geometry. It is shown that roundabouts can substantially reduce speed in the negotiation zone. The entry speed and influence zone depends on the desired speed in the upstream sections and on the roundabout geometric characteristics.

2014Journal article

Open access

Estimating the parameters of Cowan’s M3 headway distribution for roundabout capacity analyses

Publication . Vasconcelos, Luís; Silva, Ana Bastos; Seco, Álvaro; Silva, João

Capacity models based on the gap acceptance theory are widely used in unsignalised intersections and roundabout capacity analysis. !ese models are based on the statistical distribution of major vehicle headways. In this "eld, Cowan’s M3 distribution is usually recognized as the most adequate, but the estimation of its parameters is not trivial. In this paper, the main estimation methods are reviewed and a new method (Simultaneous Numerical Estimation – SNE) is proposed. !e SNE method was used to develop a calibrated relation between parameters, using "eld data collected in Portuguese roads and roundabouts. It was determined that the new formula improves capacity estimates, either in one-lane or in two-lane roundabouts. !e paper also addresses the importance of each input variable and parameter in the resulting capacity model, through a sensitivity analyses.

2012-12-13Journal article

Open access

A Comparison of Roundabout Capacity Models

Publication . Vasconcelos, Luís; Seco, Álvaro; Silva, Ana Bastos; Abreu, Tiago; Silva, João P.

In the present study four roundabout capacity models - Siegloch, Cowan M3-1L, Cowan M3-2L and TRL - are presented and compared against microscopic simulation results. The evaluation framework is centered mostly on the characteristics of the entering and circulating traffic and it is shown that the more popular models - TRL and Siegloch, are unable to generate consistent capacity estimates for the whole range of conflicting flows. The models based on Cowan M3 headway distribution are more robust but still they aren't sensible to differences in the vehicles destinations, both in the entry and in the circulating traffic. This aspect is also poorly handled by the microscopic simulation model.

2012Conference paper

Restricted access