This paper proposes a new ant colony based optimizer to improve the traffic flow in a city. For this reason, a new structure of urban traffic control system has been introduced, which uses an ant colony optimizer as its main part. To study the performance of such system, we simulated the ACO based system as an adaptive path planner. Results show a very good optimization of path length and path traffic. To apply ACO on this problem we have changed the original version of ACO and the modified algorithm can be used for other applications such as designing intelligent data routers, intelligent data mining, etc.