This article examines ways of preventing road traffic congestion from the formation of 'gridlocks' or 'superjams', where queues become embedded in the road network and very hard to clear. This process is not fully understood, because there has been very little research on jam propagation and on the effects of physical characteristics of road networks on jams. Computer simulations of gridlocks show that the number of vehicles that they enclose increase approximately as the square of elapsed time; thus early detection of a gridlock is even more important than early detection of a queue on an isolated road. Simulation models can help to find ways of reducing the rate of growth of a jam or protecting against jam formation; the problem is basically one of queue management. To handle gridlock on a particular network, the following steps need to be taken: (1) identify places where queue formation could obstruct other traffic movements, thus propagate a blockage from one part of the network to another; (2) apply dynamic or static control measures, especially traffic signal settings, to control or relocate the critical queues; (3) prevent queues from tailing back across junctions by applying special signal setting techniques. These three steps are 'static' in the sense that they do not respond automatically to changes in traffic flows. Thus, in principle, they could be improved by implementing them all in dynamic mode, using occupancy detectors to supply information about the queues. It is often useful to modify road layouts to reduce interference between queues.

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    Reed Business Information, Limited

    Quadrant House, The Quadrant
    Brighton Road
    Sutton, Surrey  United Kingdom  SM2 5AS
  • Authors:
    • Wright, C
    • HUDDART, K
  • Publication Date: 1989-7-6


  • English

Media Info

  • Pagination: p. 16-17
  • Serial:
    • Volume: 172
    • Issue Number: 5052
    • Publisher: Hemming Group, Limited
    • ISSN: 0039-6303

Subject/Index Terms

Filing Info

  • Accession Number: 00498980
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Sep 30 1990 12:00AM