The basic principle of signalization is the provision of a safe and effective means for time and space allocation at an intersection for both vehicular and pedestrian needs. The safety community concurs on the fact that there is the potential for safety improvements after signalization of an intersection, but there is a great disagreement on their magnitude as well as their potential negative operational impacts. This research reviewed the safety and operational efficiency after the installation of traffic signals at several locations throughout Kentucky. The report presented here mainly addresses the operational impacts from signal installation, since the safety aspects were addressed in a separate report.

This part of the study evaluated a subset of 32 intersections for which detailed traffic volumes were available for the before and after conditions. The basic premise that traffic signals that do not meet the appropriate warrants will have negative operational effects and have the potential for creating safety hazards was supported by the data. Overall, the analysis showed that traffic signal installations will tend to increase delays and create a lower operational efficiency than under the stop control conditions. This was more apparent for the intersections that did not meet any warrants.

The safety analysis for these intersections also showed that for unwarranted intersections safety will decrease. The only group that showed any safety improvements were those intersections where the volume and crash warrant were met indicating that the signal installation was appropriate. It is possible that there are conditions and turning volume combinations that separation of traffic movements and conflicting movements may be needed. It is therefore imperative that other options be evaluated along with the potential for signal installation in order to properly and effectively address the intersection design and requirements.

It is apparent that a more thorough review and study of the alternative options is needed prior to recommending a signal installation where not only the MUTCD warrants are to be evaluated but additional options (do nothing and roundabout) should be evaluated.

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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, the Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names or trade names is for identification purposes only and is not to be considered an endorsement.