Though satisfactory methods of estimating capacities and delays at traffic signals and t-junctions are well established, an accepted formula has not been developed for roundabout capacity which takes into account the fundamental change in the mode of operation of roundabouts. This has been due to the introduction of the priority-to-right rule in 1966. This article describes the methods of approach which are being used at Southampton and the results which have so far been produced. The roundabout is regarded as a series of simple priority t-junctions. The theory is developed first for a single entry lane to the roundabout and then extended to the general case of n entry lanes. A formula is given for the capacity of the entry point in terms of headways, the flow on the roundabout, and the acceptance gap of the entering vehicles. In order to test the formula, capacity measurements were made under saturated flow conditions at 15 entry points on roundabouts in London and Southampton. The formula shows good agreement with the measured capacities. The method of estimation of the acceptance gap and the minimum headway for entering vehicles is described. /TRRL/

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  • Corporate Authors:

    Printerhall Limited

    29 Newmart Street
    London W1P 3PE,   England 
  • Authors:
    • Armitage, D J
    • McDonald, M
  • Publication Date: 1974-10

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Filing Info

  • Accession Number: 00098107
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Oct 18 1975 12:00AM