Congestion control is a process to achieve optimal decision-making and effective control of vehicles through the interaction of vehicular perception and control, and it shows the typical characteristic of cyber physical systems. Based on the physical-world model of Konishi et al., a new control method to suppress the traffic jam is proposed in the feedback cyber physical systems under the open boundary, which considers the effect of safe headway on the traffic system from the perspective of tight conjoining between the transportation cyber system and the transportation physical system. By using the Hurwitz stability criteria and the H∞ norm theory, the condition under which the traffic jam can be well suppressed is analyzed. Comparison between our method and the previous methods is carried out. The simulation results show that the temporal behavior obtained by our method is better than those of the previous control methods, and our control method could be well applied to traffic congestion control in cyber physical systems. The simulation results are consistent with the theoretical analysis.