Revisiting Existing Warrants for Left-Turn Lanes at Unsignalized Intersections on Two-Way Roadways

This paper revisits Harmelink’s 1967 methodology for left-turn lane warrants and queue storage lengths at unsignalized intersections. Since 1967 sufficient knowledge has been gained in the area of access management, traffic engineering, and human factors to warrant revisiting the assumptions and field observations used for the methodology that is mostly used as a basis for left turn warrants at unsignalized intersections. The paper specifically investigates different gaps to clear at the 50th and 85th percentile and adjusted to the calibration factors in the Harmelink methodology for older drivers. The paper provides comparisons of the warranting volumes for the various alternatives. Findings suggest that the use of the original Harmelink methodology underestimates the need for a left-turn lane significantly, specifically when providing for the needs of older drivers. It is recommended that the calibration factors be adjusted to reflect more recent research findings and, in the case of larger older driver populations, the following values be used: a critical gap of 8 sec, a time to perform the left-turn movement of 5 sec, and a time to clear the left-turn lane of 6.6 sec.


  • English

Media Info

  • Media Type: CD-ROM
  • Features: References; Tables;
  • Pagination: 18p
  • Monograph Title: TRB 86th Annual Meeting Compendium of Papers CD-ROM

Subject/Index Terms

Filing Info

  • Accession Number: 01049531
  • Record Type: Publication
  • Report/Paper Numbers: 07-0784
  • Files: TRIS, TRB
  • Created Date: Feb 8 2007 5:22PM