Unsignalized vs signalized roundabouts under critical traffic conditions: a quantitative comparison

The paper deals with the choice among different alternatives as regard the design of urban multi-junction nodes. As known, the final choice depends on a set of evaluation criteria based on performance indices. Performance could be mainly estimated through the computation of capacity, queues, delays suffered by vehicles and the estimation of the level of service. In this context this paper focuses on evaluating the performance of roundabouts with or without signal control. In the first part of the paper a brief review of common methods used to evaluate the roundabout performance is presented, in order to compare their results in different roundabout layouts and in various traffic situations. In particular, the behaviour of methods is analysed in critical traffic situations, such as in conditions near or over capacity. In these cases, when the degree of saturation exceeds a certain level, the performance of the roundabout worsens rapidly, particularly over short periods of time, as well-known in the scientific literature. In this case queues may form and delay begins to increase exponentially and small changes in volume have large effects on the level of service. The results given by the application of different methodologies to not-signalised roundabouts are then discussed. In such critical situations it is quite interesting to take into consideration the possibility of introducing traffic control devices. Of course it is also necessary to evaluate the performance of this signalised node in the same critical traffic conditions. In other words the aim is to estimate the same indices as before in order to perform a correct comparison between the two alternatives. A mesoscopic model is used to analyse the behaviour of this particular signalised multi-junction node. The model describes flows in terms of platoons of vehicles moving from signal to signal. Each platoon is identified by few elements and its behaviour depends on the signal plan and on interactions with other platoons. The model uses geometric constructions based on events modifying the system and it preserves information related to platoons crossing the node. The results enable estimation of queues and delays suffered by different traffic flows. With reference to some existing multi-junction nodes, the results given by the previous approaches are discussed in order to determine if and when a signalised condition could improve the level of service of a unsignalised roundabout. Moreover also some quantitative estimations of these improvements are presented. For the covering abstract see ITRD E126595.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/0860503429
• Authors:
  • BERNETTI, G
  • DALL''ACQUA, M
  • LONGO, G
• Publication Date: 2003

Language

• English

Media Info

• Pagination: 18pp
• Monograph Title: Risk aversion and route choice decisions
• Serial:
  • PROCEEDINGS OF THE EUROPEAN TRANSPORT CONFERENCE (ETC) 2003 HELD 8-10 OCTOBER 2003, STRASBOURG, FRANCE
  • Publisher: Association for European Transport (AET)
  • ISSN: 1474-9122

Subject/Index Terms

• TRT Terms: Conferences; Decision making; Highway capacity; Improvements; Level of service; Roundabouts; Traffic congestion; Traffic signals
• ITRD Terms: 643: Capacity (road, footway); 8525: Conference; 632: Congestion (traffic); 2248: Decision process; 9108: Improvement; 653: Level of service; 438: Roundabout; 565: Traffic signal
• Subject Areas: Highways; Operations and Traffic Management; I71: Traffic Theory; I73: Traffic Control;

Filing Info

• Accession Number: 01014658
• Record Type: Publication
• Source Agency: Transport Research Laboratory
• ISBN: 0-86050-342-9
• Files: ITRD
• Created Date: Dec 22 2005 3:07PM