Urban Transportation Vehicle Sustainability Assessment with a Comparative Study of Weighted Sum and Fuzzy Methods

Sustainability assessment in transportation planning and selection of the best transportation mode among alternatives is a challenging process. The technological differences among conventional, hybrid, and alternative fuel vehicles and buses, the large number of variables in the sustainability assessment of transportation systems, and the subjective judgment of decision makers introduce uncertainty. The objective of this paper is thus twofold: (1)to demonstrate a sustainability framework that focuses specifically on vehicle characteristics and (2)to compare two multicriteria decision making (MCDM) methods in terms of ranking sustainability performance of transportation vehicles and applicability to selected indicators. The two most widely adopted MCDM methods for decision making were used, the weighted sum method for its simplicity and the fuzzy logic method for its ability to incorporate imprecise and vague information. The assessment includes five vehicle types and various mode share scenarios. The results from the two methods were compared by using traffic composition data by vehicle technology from a 33.2-km (20.6-mi) network in urban Honolulu. Both methods provided vehicle rankings on a continuous scale and integrate vehicle technology and fuel characteristics in the assessment. The differences between the two methods appear to be systematic with the weighted sum method generating results with greater fluctuations. The fuzzy logic method is more stable. It is also more flexible because it is capable of incorporating quantitative and qualitative judgment criteria.