This paper presents detection and classification ofmoving Thai vehicles based on traffic engineering knowledge.The proposed technique consists of two main parts as follows.The first part is the detection of moving vehicles using imagetracking methods e.g. background and foreground (BG/FG)detection and blob tracking. Such methods can provide thevalues of vehicle features such as position, length (L) and width(W). The second part is the classification of Thai vehicles basedon traffic engineering knowledge which is traffic managementfor not only controlling traffic lights on a crossroad but alsocalculating volume/capacity ratio and queue length. ThereforeThai vehicles normally can be separated into five groups i.e.first: bicycle, motorcycle and motor tricycle (Tuk-Tuk);second: passenger car, pickup, van and passenger pickup;third: six-wheel truck and mini bus; fourth: ten-wheel truckand big bus; fifth: eighteen-wheel truck and trailer. Fromabove reasons, the second part uses the key features of size (W,L and W/L ratio) from each group which are applied to adecision-tree method for classifying Thai-vehicle groups. Theresult shows that the use of one input feature is sufficient forthe differentiation between 4-group with an overallclassification accuracy of 97.37%.