SOME FACTORS AFFECTING RURAL SPEED/FLOW RELATIONS. A STUDY OF RURAL SPEED/FLOW RELATIONS WHERE A HIGH PROPORTION OF HEAVY VEHICLES OCCURS ON STEEP GRADIENTS

The author explains that speed/flow relationships normally used for rural transportation studies are those derived by the Transport and Road Research Laboratory (TRRL), United Kingdom, mainly during 1968. Since then some high standard roads have been built through more difficult terrain, and the proportion of commercial vehicles using the roads is often higher than average. This paper presents information on a study undertaken to formulate a set of speed/flow curves, based on the TRRL work, which would incorporate revisions wherever real evidence of variations was found. Four different survey methods were used at eight sites (seven being dual-carriageways) selected where high proportions of heavy vehicles occurred on steep gradients. Survey details are presented. Multiple regression analysis was used to analyse all the speed/flow observations taken, and the results are given in tabulated form and as a series of speed/flow result curves for each site. The results are discussed. The final results of this study are presented as a set of proposed speed/flow curves in which the author has incorporated a number of refinements based on the following conclusions: (1) speeds on motorways are influenced by gradients in a similar manner to those on dual-carriageway, all purpose roads, and therefore the hilliness factor from TRRL report lr651 should be included in the motorway equation. (2) on all types of road where a high proportion of heavy vehicles occur on steep gradients, speeds tend to be lower than those calculated using the lr651 relationship. (3) on dual two-lane carriageway roads where high hilliness factors occur, the speed/flow curve tends to be a straight line with a negative slope. /TRRL/

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  • Corporate Authors:

    Printerhall Limited

    29 Newmart Street
    London W1P 3PE,   England 
  • Authors:
    • Farthing, D W
  • Publication Date: 1977-1

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Filing Info

  • Accession Number: 00156455
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: Oct 13 1977 12:00AM