LEFT-TURN LANE INSTALLATION GUIDELINES

The addition of a left-turn lane can improve the operations and safety at an intersection. Guidelines as to when to include a left-turn lane in intersection design are plentiful. Because of the quantity of methods, questions are asked regarding which method to use. This paper reviewed eight selected techniques and a number of criteria present in state manuals. Methods based on delay typically do not recommend a left-turn lane at lower left or through volumes when compared to methods based on conflict avoidance or safety. Because of the high benefits for crash reductions provided by left-turn lanes, a method that results in a recommendation at lower volumes would be preferred. The Harmelink model is a widely accepted approach that is based on conflict avoidance. The procedure was first proposed in 1967 and includes assumptions that may need to be revised. Findings from current research would suggest a critical gap of 5.5 sec (rather than 5.0 sec), a time to make left turn of 4.3 sec (rather than 3.0 sec), and a time to clear the lane of 3.2 sec (rather than 1.9 sec). A table was developed that lists suggested guidelines for installing left-turn lanes for operating speeds of 30, 50, and 70 mph (50, 80, and 110 km/h).

Language

  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; References; Tables;
  • Pagination: 22p
  • Monograph Title: 2ND URBAN STREET SYMPOSIUM: UPTOWN, DOWNTOWN, OR SMALL TOWN: DESIGNING URBAN STREETS THAT WORK, JULY 28-30, 2003, ANAHEIM, CALIFORNIA

Subject/Index Terms

Filing Info

  • Accession Number: 00989172
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Apr 8 2005 12:00AM