A cellular automata model is presented to simulate the traffic flows on a main road in city network in which there are traffic lights at the intersections.We have investigated how the traffic shock wave forms and how it spreads.It is found that the traffic flows have several peak values.When the distances between the intersections are equal,for a fixed value of cycle times of the traffic lights,the current does not depend on the density of vehicles for a range of density.For a high density,when the distance between the intersections is greater than a certain value,the traffic flow maintains constant.