¹Phase diagram distortion from traffic parameter averaging

Motorway traffic congestion is a major bottleneck for economic growth. Therefore, research of traffic behaviour is carried out in many countries. Although well describing the undersaturated free flow phase as an almost straight line in a (k,q)-phase diagram, congested traffic observations and theories disagree in the oversaturated, forced flow state. The relation between traffic observations and the structure of the phase diagram was investigated. The way speed observations are averaged and how this influences the location of the averaged observations in the phase diagram are considered. Theoretical analysis suggests a phase diagram where the oversaturated phase consists of a straight line. This straight right branch corresponds to upstream moving speed wave regions, called speed waves. The right branch connects the top of the free flow phase line with a point of maximum k and zero q. Its slope corresponds to the speed of the speed wave, with a value of -18?1 km/h. In practice, however, average traffic states are normally observed below this line, introducing a paradox. The most commonly used models and theories, and the paradoxical results, are treated using both single location traffic data, and data gathered from consecutive locations along a road segment (multi location data). These data consist of one-minute arithmetic averaged speed flow observations. From mean speed v and flow q the mean density k is derived, to obtain observations in the (k,q)- phase diagram. a triangular phase diagram based on a simple car following theory by Newell is proposed which is in agreement with multi location observations. Data from Dutch motorways were shown to be paradoxical. Multi location data agree with the triangular model, but single location data do not. By simulating single location average speed flow data, generated from traffic flow that follows the triangular phase diagram, it is shown that single location averages strongly depend on the speed averaging method. As a consequence, traffic observations based on averaged speeds may give rise to far higher mean speeds, and lower densities than car drivers' actually experience. For the covering abstract see ITRD E145999

• Record URL:
  https://aetransport.org/past-etc-papers/conference-papers-pre-2012/conference-papers-2008
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/14749122
• Authors:
  • STIPDONK, H
  • VAN TOORENBURG, J
  • POSTEMA, M
• Publication Date: 2008

Language

• English

Media Info

• Pagination: 13p
• Serial:
  • EUROPEAN TRANSPORT CONFERENCE 2008; PROCEEDINGS
  • ISSN: 1474-9122

Subject/Index Terms

• TRT Terms: Average travel speed; Calculation; Conferences; Freeways; Information processing; Mathematical models; Speed; Traffic flow; Waves
• Geographic Terms: Netherlands
• ITRD Terms: 5409: Average speed; 6464: Calculation; 8525: Conference; 8655: Data processing; 6473: Mathematical model; 2752: Motorway; 8078: Netherlands; 5408: Speed; 671: Traffic flow; 6767: Wave
• Subject Areas: Data and Information Technology; Highways; Operations and Traffic Management; I71: Traffic Theory;

Filing Info

• Accession Number: 01174642
• Record Type: Publication
• Source Agency: TRL
• Files: ITRD
• Created Date: Sep 30 2010 11:16AM