Theory-based numerical models tend to use complicated model structure, so it is not always easy to understand and theorize the findings of those models. Yu and Rhee (2011) provide a methodology that can simplify the rate of welfare change in policy variables in the models a la Anas and Kim (1996). We generalize their methodology to the models with the constant-returns-to-scale production function and apply the methodology to the welfare analysis of congestion tolls.