Warrants for the installation of left-turn phasing were developed. A review of literature was conducted along with a survey of the policies of other states. Field data of delays and conflicts were taken before and after installation of exclusive left-turn signalization. Left-turn delay studies were conducted at intersections with varying volume conditions. Analysis of the effect on accidents of adding a left-turn phase was made. The relationship between left-turn accidents and conflicts was investigated. Other types of analyses concerning gap acceptance, capacity, and benefit-cost ratios were also performed.

It was found that exclusive left-turn phasing significantly reduced left-turn accidents and conflicts. This reduction was offset in part by an increase in rear-end accidents. Left-turn delay was reduced only during periods of heavy traffic flow. Total delay for an intersection increased after installation of left-turn phasing. Warrants were developed dealing with the following four general areas:

  1. accident experience,
  2. delay,
  3. volumes, and
  4. traffic conflicts.

Report Date


Report Number

No. 505

Digital Object Identifier



Offered for publication by the Transportation Research Board.