The paper addresses a decentralized control problem of traffic flow. Most existing freeway traffic flow control relies on centralized scheme to adjust the control variable in order to enhance efficiency and avoid congestions. The paper devises a cellular framework and decentralized control scheme for traffic flow control so that the control scheme does not rely on global information. The proposed control scheme exploits neighboring cellular information and sliding mode control technique to prevent the buildup of traffic flow and aggravating propagation of shock waves. The proposed traffic flow controller is simulated to show its effectiveness in attenuating shock waves and fluctuations.