We consider an urban network with two traffic modes. We control the traffic lights in order to free the roads used by the public transport vehicles. To do this, we solve a flow assignement problem, from which we deduce an ideal distribution of private vehicles. Then using traffic lights, we design a regulator maintaining the car distributions in the roads around the ideal trajectory. This regulator is obtained by solving a linear quadratic problem. The result is a global feedback on the car numbers in the roads. We show the robustness of the obtained control. We compare the obtained results with those given by Bhouri and Lotito (2005).