Grey relation analysis (GRA) was utilized in this study to capture the dynamic characteristics of different factors in the transportation system during their development process and to evaluate the relative influence of the fuel price, the gross domestic product, the number of motor vehicles and the vehicle kilometers of travel (VKT) per energy increase. Furthermore, results from this method were then compared with the OECD decoupling index. This comparison revealed that the steady growth of economic development was strongly correlated with vehicular fuel consumption. The relation grade of 0.967 implies that the increase in the number of passenger cars was another important factor for energy increase. As for the motorcycles, the relative influence of VKT was insignificant, and the positive relationship to G(FK) indicated that the performance of vehicular energy efficiency has improved in recent years. In comparison to the other factors, the contribution of fuel price was obscure. Additionally, the analysis of decoupling effects also yielded similar results to those of GRA. The coupling index between economic growth and fuel price was observed for passenger cars and motorcycles, while the VKT was relatively decoupled. (C) 2008 Elsevier Ltd. All rights reserved.