Guidelines for Left-Turn Bays At Unsignalized Access Locations

• Authored by:  Dr. Vergil G. Stover
• Co-authored by:  Pat Hawley

Hawley, P. E., and V. G. Stover, “Guidelines for Left-Turn Bays At Unsignalized Access Locations,” Proceedings for the 1996 National Conference on Access Management (1996), pp. 383-391.
The primary focus of this research effort was to better understand how left-turning traffic affects the operation of through traffic at an unsignalized intersection. Prior to this paper, warrants for auxiliary lane installations were based on delay to turning traffic with little consideration for through traffic operations. The study focused only on four-lane undivided arterial streets with constant (non-platoon) traffic flow. The researchers used iterative simulation runs to determine the point at which left-turn volumes significantly impacted the delay incurred by through vehicles. These volumes were then used to create the graph shown in Figure 3, in which a left-turn lane would be warranted for traffic volumes above and to the right of each line. The guidelines developed through this research effort are commonly referred to as the TTI Warrant Method.