This paper describes experiments carried out by the Transport and Road Research Laboratory on public roads, to determine ways of improving the capacity of large roundabouts without increasing their size. Within the same area of road similar capacities have been obtained with two radically different designs; on one hand, the usual one-way clockwise circulation around the central island and, on the other hand, a ring junction consisting of two-way circulation around the central island with a mini-roundabout at the mouth of each road. By reducing the size of the central island the full capacity can be increased by more than 30 per cent but special care may then be required to deflect and slow down the fast crossing movements. By fuller use of the area at the mouth of each road between the existing outer kerblines (including the area of any median strip or island), the full capacity of a six-arm roundabout has been increased by about 15 per cent. At one particular site, by marking a left turning filter lane from one entry to the adjacent exit, the discharge capacity of the affected approach road has been increased by 36 per cent without reducing the roundabout circulating flow. The range of applicability of the alternative designs presented in the paper are discussed. /Author/

  • Supplemental Notes:
    • Presented at Seminar W (Road Design 2: Specialist Topics) of the PTRC Summer Annual Meeting, Warwick University, England, 8-12 July 1974.
  • Corporate Authors:

    Planning and Transport Res and Computation Co Ltd

    167 Oxford Street
    London W1R 1AH,   England 
  • Authors:
    • Blackmore, F C
    • MARLOW, M
  • Publication Date: 1974-7

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Filing Info

  • Accession Number: 00096305
  • Record Type: Publication
  • Report/Paper Numbers: PTRC/P/109
  • Files: TRIS
  • Created Date: Sep 10 1975 12:00AM