This paper combine the concept of reserve capacity with the continuous equilibrium network design problem, an integrated method is used to maximize the reserve capacity of a road network. On the one hand we try to find the maximum possible increase in traffic demand by setting traffic signals at individual intersections. On the other hand, we increase the road capacity in order to increase the whole capacity of a road network. In view of the characteristic of mixed traffic flow in road network, we proposed a multimodal bi-level programming model which fully considered the interaction of different vehicle classes and influence upon the network reserve capacity by budget. The proposed model was solved by a solution algorithm based on extremum disturbed and simplified particle swarm optimization (dsPSO). Numerical experiment results show that capacity of O-D pairs are in direct ratio with the total available budget, only if O-D demand multiplier of all vehicle classes tend to be about equal the benefit of all users can be guaranteed, and the convergence performance of dsPSO in dealing with the traffic model is good after disturbance factors were introduced into PSO.