This paper introduces a new approach to design a vehicle detection module using a microwave motion sensor in order to obtain vehicle length and vehicle speed. The design of this module aims to apply for Intelligent Transport System (ITS) in which it plays a role as a unit of Traffic Detectors with Inductive Loops, Video, Infrared Sensors, etc. The module has advantages of using low power, costing low price and especially providing reliable results for measuring vehicles. The output signal of the microwave motion sensor is a low-level voltage whose frequency (Doppler) represents the speed at which a vehicle is moving towards or away from the sensor. We process this signal to get information about length and speed of the vehicle. We implemented the method in a microwave motion sensor named HB100 to measure the movement in radius of 8[m] in line-of-sight, vehicle speed range from 5[km/h] to 40[km/h]. We achieved the accuracy of more than 80% in 100 times observing a specific vehicle in a specific speed range.