This document provides a literature review of different techniques used for traffic signal control systems. It discusses traditional methods like traffic police and automatic traffic signals. It also reviews intelligent approaches using image processing and wireless sensor networks. Image processing methods use cameras to detect vehicle numbers and adjust signal times accordingly. Wireless sensor network methods place sensors along roads to detect traffic and communicate with a central control box to optimize signal timing. The document concludes the wireless approach has benefits over existing methods by allowing large-scale deployment at low cost.