A NOTE ON SPEED/FLOW/CONCENTRATION RELATIONS

The author examines the use of speed/flow and speed/concentration plots. Often the speed/flow data show a large amount of scatter and the corresponding speed/concentration plots show a marked tendency to which a downward straight line may be fitted. This straight line can be reconverted to a parabola on the speed/flow diagram, establishing a significant relationship between the two variables which are totally uncorrelated giving a false measure of capacity. Normally distributed random values of speed are used to illustrate the abuse of the relation. A further danger in the transformation process is that several rectangular hyperbola give an equally good fit to the speed/concentration data as the straight line; it is shown that these produce significant changes in the shape of the reconstructed parabola on the speed/flow diagram. The shape and statistical significance of a speed/flow relation should not be inferred from a speed/concentration relation unless the latter is very clearly defined over a range of values. /TRRL/

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/00410683
• Corporate Authors:

  Printerhall Limited

  29 Newmart Street
  London W1P 3PE,   England 
• Authors:
  • Duncan, N C
• Publication Date: 1976-1

Language

• English

Media Info

• Features: Figures; Tables;
• Pagination: p. 34-35
• Serial:
  • Traffic Engineering & Control
  • Volume: 17
  • Issue Number: N1
  • Publisher: Hemming Group, Limited
  • ISSN: 0041-0683
  • Serial URL: http://www.tecmagazine.com/

Subject/Index Terms

• TRT Terms: Charts; Geometric curves; Highway capacity; Significance (Statistics); Speed; Statistical dispersion; Statistical sampling; Statistics; Traffic density; Traffic flow; Traffic speed
• Old TRIS Terms: Dispersion; Hyperbolas
• ITRD Terms: 643: Capacity (road, footway); 6486: Chart; 6512: Dispersion (stat); 6553: Sample (stat); 6532: Significance (stat); 5408: Speed; 673: Traffic concentration; 671: Traffic flow
• Subject Areas: Data and Information Technology; Highways; Operations and Traffic Management; Planning and Forecasting; I71: Traffic Theory; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 00139002
• Record Type: Publication
• Source Agency: Transport and Road Research Laboratory (TRRL)
• Files: ITRD, TRIS
• Created Date: Nov 17 1976 12:00AM