The required length of left-turn lanes at unsignalized intersections of two-lane roadways is analyzed, and recommended lengths are presented for different conditions. Increasing volumes of turning movements along suburban roadways due to residential and commercial developments warrant an analysis of the adequate length of turn lanes. The existing guidelines and standards for determining lane lengths at unsignalized intersections are incomplete, and the practices of various state agencies are not uniform. A model is developed which calculates the probability that a given length of turning lane will result in overflows. Lane lengths are suggested such that the probability of lane overflow is less than a given threshold value. The parameters considered in the model are the volume of turning vehicles, volume of opposing vehicles, critical gap, threshold probability, and vehicle mix. The validity of the model is checked by computer simulation. The recommended lengths are compared with lengths suggested by AASHTO, and the effects of considering opposing volume and changing the values of the threshold probability are discussed. The results of a field survey on the required space per vehicle in the turn lane are also presented. Recommended lane lengths for various conditions are presented in a set of tables.


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 193-201
  • Monograph Title: Geometric design, roadside safety features, roadside hardware monitoring, and scenic loop tours
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00715008
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Dec 26 1995 12:00AM