Traffic congestion in current large metropolitan cities has been substantially increasing since the 1950s. This can be primarily attributed to the enormous increase in vehicles’ private ownership due to rapid urbanization and economic growth. The primary issue with congestion is that it causes various externalities, including incidents, delays, and pollution. The increase in pollution affects human health, the globe, and the economy by increasing harmful pollutants, GHGs, and transportation expenditures. Although increasing transportation infrastructure capacity has been used to relieve congestion, researchers and experts realized that such a solution is costly and must be accompanied by operating existing capacity more efficiently.
Optimizing traffic signal timings is one of the critical strategies for addressing the congestion problem. The first adjustments to traffic signal timings were made to make traveling safer, more reliable, and more convenient. Later, other essential objectives (beyond safety) were sought when adjusting traffic signals, namely reducing delays and travel time by reducing the idling times and unnecessary stops. The oil crisis of the early 1970s raised concerns about the amount of fuel consumed in traffic. This concern spread to all segments of traffic operations, and it eventually raised the question of how signalized intersections can be accommodated to minimize fuel consumption. Hence, nowadays, proper signal timing optimization is not only essential to regulate traffic flow, ease congestion, and improve mobility, but also acts as a valuable strategy to create a sustainable traffic environment.