The Performance Index (PI), a widely used composite measure of vehicular stops and delays, is one of the most popular traffic signal performance measures. Over the decades it has been used to achieve a proper balance between delays and stops. Its key component, the “stop penalty,” has been used to minimize excess fuel consumption from unnecessary stops caused by traffic control operations. In signal optimization practice this stop penalty, also known as the K factor, has been set as an invariable parameter with a relatively low value ∼10 to 20. This paper questions this widely accepted practice. It first explains the origins and meaning of the PI and the significance of the K factor. Then, it lists various studies, discusses their inconsistencies, and introduces a new Fuel Consumption Intersection Control PI (FCIC-PI). The paper also presents findings from field data collection and compares them with the other studies, including some simulation results. Outcomes of these various findings show some inconsistencies, but all point to the existing practice being wrong: the K factor is a variable dependent on at least one important factor—cruising speed. The outcomes also indicate that K values should, if fuel consumption is to be minimized, be larger than currently used. Future research should confirm these findings with a larger field data set, investigate other factors that affect the stop penalty, and consider a family of other emission-related PIs. Finally, a new methodology should be developed to properly integrate these new PIs into signal timing optimization.

Traffic simulation and optimization tools are classified, according to their practical applicability, into two main categories: theoretical and practical. The performance of the optimized signal timing derived by any tool is influenced by how calculations are executed in the particular tool. Highway Capacity Software (HCS) and Vistro implement the procedures defined in the Highway Capacity Manual, thus they are essentially utilized by traffic operations and design engineers. Considering its capability of timing diagram drafting and travel time collection studies, Tru-Traffic is more commonly used by practitioners. All these programs have different built-in objective function(s) to develop optimized signal plans for intersections. In this study, the performance of the optimal signal timing plans developed by HCS, Tru-Traffic, and Vistro are evaluated and compared by using the microsimulation software Vissim. A real-world urban arterial with 20 intersections and heavy traffic in Fort Lauderdale, Florida served as the testbed. To eliminate any bias in the comparisons, all experiments were performed under identical geometric and traffic conditions, coded in each tool. The evaluation of the optimized plans was conducted based on average delay, number of stops, performance index, travel time, and percentage of arrivals on green. Results indicated that although timings developed in HCS reduced delay, they drastically increased number of stops. Tru-Traffic signal timings, when only offsets are optimized, performed better than timings developed by all of the other tools. Finally, Vistro increased arrivals on green, but it also increased delay. Optimized signal plans were transferred manually from optimization tools to Vissim. Therefore, future research should find methods for automatically transferring optimized plans to Vissim.