The document describes a modification to the Multielement Genetic Algorithm (MEGA) called H-MEGA to optimize traffic light signal parameters and reduce traffic congestion. H-MEGA adds a hash table to store the best populations found so far to guide the recombination process. Testing showed H-MEGA improved vehicle throughput over the original MEGA and Particle Swarm Optimization methods by 10-21% on a road network in Kumamoto City, Japan.