In an exceptionally urbanized world, public transport seems to be more important than ever as it contributes for more sustainable, accessible cities. In an attempt to assist both government agencies and private companies on constructing efficient transport networks, we propose a integer linear programming model to design a demand optimal line with respect to a budget constraint. This text explores particularities of street level transport but the model can be easily generalized for other modes. Preliminary results for grid networks of several sizes and densities were reported.