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.