Abstract: It is difficult to analyze operating speed on freeways using current vehicle classification schemes because of less maneuverability and ambiguous boundaries.Based on the relationship between speed and wheelbase on the investigated sections,a new vehicle classification scheme is presented in this paper,using cluster analysis method by the wheelbase.All vehicles are separated into 3 categories depending on wheelbase: small vehicles,the wheelbases of which are not more than 5 meters;medium vehicles,more than 5 meters and less than or equal to 10.5 meters;and large vehicles,more than 10.5 meters.In this vehicle classification scheme,the 3 categories have distinct speed distributions which can describe the operating speed better.