Performance and Safety Roundabouts with Traffic Signals

AbstractThe paper presents designs, advantages and some drawbacks of various layouts of roundabouts with traffic signals, used in urban arterials on crossings with large traffic volumes. The authors analyze signal settings with alternative phasing used at intersections that can provide the intersection capacity of about 6500 veh/h in 2x2 lanes arterials or even 8000 veh/h in 2x3 lanes arterials. Accident statistics for roundabouts with traffic signals in Krakow are also given and discussed. In addition, presented are practical examples of changes of signalized roundabouts geometry; reconstruction into a form of turbo-roundabout and its effects regarding traffic safety and good performance

Variability of Capacity and Traffic Performance at Urban and Rural Signalised Intersections

AbstractUrban and rural intersections differ in terms of functionality. They support traffic which differs in terms of travel goals and motivations. In urban areas, these goals are mainly related to work, home, shopping and recreation. On the other hand, rural intersection mainly support through traffic between towns and cities and regions, with a small admixture of local traffic. Comparison of the characteristics of traffic flows indicates that towns and cities have heavier traffic flows, mainly of light vehicles, and frequent congestion states, while rural areas reveal smaller traffic flow and its structure is more diverse and involves vehicles travelling at higher speeds. The structure of traffic directions at rural intersections, usually dominated by traffic moving along one of the intersecting roads, differs substantially from the structure of the same at urban intersections. In order to control traffic, rural intersections increasingly rely on varied in time traffic signals, with a preference strategy whenever there is absence of excitation of motion detectors by the participants. The scope of intersections expansion and traffic control algorithms are more varied at urban intersections. Rural intersections are mainly controlled based on three major driving phases. Differences in intersections locations and the specificity of traffic conditions and traffic control imply drivers’ different needs and behaviour. Hence it is important to conduct comparative analyses of urban and rural intersections. The paper will present analysis of variability of saturation flows and capacity and traffic performance based on empirical studies of intersections in 2008 – 2012, both in urban and rural areas. Differences in drivers’ needs and behaviour in rural areas, the specific distribution of types of vehicles and directions on the lanes (single carriageway and dual carriageway) translate into slower vehicle service processes. Smaller values of saturation flow and capacity in rural areas mean that significant periodic increases in traffic flow lead to congestion states much faster than in urban areas. Although in rural areas these states are rather rare for the main direction, they are much more common at entries to the main road. The seasonal variability of traffic makes the functioning of these intersections differ between business (non-recreational) and recreational traffic (e.g. during the holiday season). The paper will also address the issue of acceptance of difficult traffic conditions in the states of traffic overload from the point of view of the road managers and the driver, referring to the reliability of intersection entries in urban and rural areas