Operational Criteria for Spanish Two-Lane Highways: Passing and Alignment Considerations

The effect of highway bendiness on traffic performance is not directly addressed on the current HCM (Highway Capacity Manual) analysis procedure for two-lane highways. Given the relationship between operating speed and horizontal alignment, highway bendiness could potentially affect speeds and platooning; and, it may be risky to use design speed in estimating free-flow speeds at segments with high bendiness. Moreover, HCM considers the effect of passing restrictions through the percentage of no-passing zones; which can lead to quite unrealistic results. The objective of this research is to evaluate the effect of passing restrictions and highway alignment variations on two-lane highway operation and incorporate it in the analysis methodology, if significant. The influence of horizontal and vertical alignment on their traffic operation was studied on 19 uniform segments from Spanish two-lane highways using TWOPAS. Alignment was classified following the German procedure: curvature change rate (CCR) and class of gradient. Passing restrictions were studied on straight segments. Percentage of no-passing zones and average passing zone length were considered. The results indicate that solely geometry was not enough to characterize traffic operation on the most linear alignments, and passing restrictions should be also included. These results can be applied to evaluate traffic efficiency on two-lane highways, in replacement of the HCM.

  • Supplemental Notes:
    • This paper was sponsored by TRB committee AHB40 Standing Committee on Highway Capacity and Quality of Service.
  • Corporate Authors:

    Transportation Research Board

    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Authors:
    • Moreno, Ana Tsui
  • Conference:
  • Date: 2017


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; References; Tables;
  • Pagination: 13p
  • Monograph Title: TRB 96th Annual Meeting Compendium of Papers

Subject/Index Terms

Filing Info

  • Accession Number: 01622723
  • Record Type: Publication
  • Report/Paper Numbers: 17-00287
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 8 2016 10:00AM