A large number of traffic accidents at signalized intersections on high-speed roadways occur during or just after the change interval. The green extension system (GES) has been used extensively in Kentucky as a method of alleviating the problem related to the dilemma zone. An alternate method of handling this problem involves warning drivers that the signal indication is about to change from green to red using advance warning flashers (AWF). The objectives of this study were: 1) to evaluate the alternative methods (GES or AWF) which can be used to lessen the problem associated with the dilemma zone which occurs at traffic signals, specifically on high-speed roadways and 2) to determine conditions where use of the AWF may be needed.

The GES was judged to be effective and its use was recommended to be continued at high speed intersections. The use of an AWF should be limited to locations where either an existing or high potential accident problem exists. Guidelines and evaluation factors to consider in determining the use of an AWF were identified. These factors included: accident history, speed limit, truck volume, sight distance, grade, red light violation rate, traffic volume, and adjacent bridge deck. The design of an AWF was discussed.

Report Date


Report Number


Digital Object Identifier



The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky or Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation.