Effects of Rainfall and Heavy Vehicles on Speed-Flow Relationship for Multilane Expressways in Japan

Many studies on factors affecting traffic speed have been conducted thus far. However, there are factors that have not been sufficiently clarified because of insufficient speed samples. In this study, samples from 641 study sites over 4 years were collected utilizing a nationwide traffic detector database of expressways in Japan and were analyzed to clarify the effects of rainfall and heavy-vehicle ratio on the uncongested speed-flow relationship on multilane expressways in Japan. In addition, the speeds that are not affected by other vehicles, called solitary-vehicle speeds in this paper, were also analyzed with the samples satisfying the criterion of 1 passenger car per lane in a 5-min time interval, which is the aggregation unit of the traffic database used here. However, there were many inappropriate samples for the analyses in the data set; thus, data elimination was carried out before analyses. As a result, it was found that even 1 mm of rainfall increment reduced speed, and the change of rainfall from 0 to 1 mm resulted in the greatest reduction in speed. Also, as flow increased, speed reduction caused by heavy vehicles also increased even at the same heavy-vehicle ratio. Thus, rainfall and heavy-vehicle ratio should be considered carefully if speed is the measure of effectiveness used for the evaluation of quality of service.


  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; References; Tables;
  • Pagination: 14p
  • Monograph Title: TRB 86th Annual Meeting Compendium of Papers CD-ROM

Subject/Index Terms

Filing Info

  • Accession Number: 01049296
  • Record Type: Publication
  • Report/Paper Numbers: 07-1933
  • Files: TRIS, TRB
  • Created Date: Feb 8 2007 6:39PM