Fuzzy mathematical programming for traffic safety planning on an urban expressway

Traffic safety planning has received increased attention because a number of accidents still occur on urban area transportation networks. The optimization approach, using budget constraints, is applicable to many problems of infrastructure planning that must be carried out under these circumstances. The problems of choosing which traffic safety facilities to construct on urban expressways are investigated in this study. This type of economic problem is formulated as an optimization of combinations problem. Incremental benefit-cost analysis and Dynamic Programming using fuzzy budget constraints are introduced. Particularly, the standard algorithm normally used to solve this problem is modified, because the fuzzy goal is defined as a step function in this type of problem. In addition, the shapes of the membership functions of fuzzy constraints are also discussed. The facts from a case study of the Hanshin Expressway (in the Kansai area of Japan) will be presented to illustrate how fuzzy theory improves the theoretical congruence with reality and adds robustness to actual traffic safety planning.