Cellular automaton traffic models can include various .factors in traffic systems and the corresponding conutational simulations are rather simple and effecive, The Billam-Middleton model (BML model facilitates the simulation of twodimensional traffic flow problems via the cellular automaton models . In this paper , the BML model is improved by removing its limitation of syncronized change of trafficlights. In the new model, the traffic light at each crossing could arbilrarliy , change its starting time and tempo of variution, and hence thc model more more realitically describe the influence of traffic lights on the performance of traffic systems . Some new effects appearing in the new nodel are also elucidated.