This article considers the question whether an implied speed/flow relationship, and hence carriageway capacity, based on an apparently satisfactory speed/concentration curve fitted to real traffic data, can be accepted with confidence. A polynomial curve had been fitted to speed and concentration data obtained from a European motorway, and carriageway capacity had been estimated from the speed/flow curve obtained through the relationship "flow = speed X concentration'. But further consideration of the original speed/concentration graph revealed a discontinuity. A fresh analysis, in which two straight lines replaced the polynomial curve gave an equally good fit to the data, and resulted in three new capacity values, the highest being 37 per cent above the lowest - and all derived from speed/concentration lines of good fit over a wide range of data. It is therefore suggested that the translation of speed/concentration data into other forms needs careful interpretation, especially if part of the data could have resulted from traffic conditions downstream of the measuring point. (TRRL)

  • Availability:
  • Corporate Authors:

    Printerhall Limited

    29 Newmart Street
    London W1P 3PE,   England 
  • Authors:
    • Duncan, N C
  • Publication Date: 1979-10

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Filing Info

  • Accession Number: 00310325
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS
  • Created Date: Feb 6 1981 12:00AM