Review of Percent Time Spent Following (PTSF) as Performance Measure for Two-Lane Highways

Percent Time Spent Following (PTSF) is implemented by the Highway Capacity Manual (HCM) as a key service measure for evaluating the level of service of two-lane highways. However, to measure PTSF directly in the field is complicated. Because of this complication, estimation of PTSF based on analytical procedure, which uses equations derived from simulations and field observations at a given location based on surrogate measure, as the percent of vehicles traveling with headway less than three seconds (3s). Findings from existential studies confirmed that analytical procedures used in HCM in evaluating PTSF yield results that are irreconcilable with the 3s surrogate measure and mostly overcapitalize the indicator. This paper presents a review on the estimation of PTSF on two-lane highways and suggest a presumptive approach to affirm the application of the current practice. Further, the authors of this paper argued that the use of 3s as surrogate for estimating PTSF based on field observation at a specific point may not represent the actual time spent following over a long segment of two-lane highways since PTSF is a space-related measure. Hence, the authors suggested the use of a test vehicle approach and to find out the different approach for heterogeneous traffic conditions on highway segments. It is expected that the views and suggestions offered will contribute to advancing a performance analysis of two-lane highways for Indian conditions.

  • Availability:
  • Supplemental Notes:
    • Abstract reprinted with permission from the publisher.
  • Authors:
    • Vivek
    • Parti, Raman
    • Singh, Indrasen
  • Publication Date: 2019-4


  • English

Media Info

  • Media Type: Print
  • Features: References; Tables;
  • Pagination: pp 23-28
  • Serial:
    • Indian Highways
    • Volume: 46
    • Issue Number: 4
    • Publisher: Indian Roads Congress
    • ISSN: 0376-7256

Subject/Index Terms

Filing Info

  • Accession Number: 01685418
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Nov 7 2018 4:14PM