This paper describes the tracking of a vehicle by using a 3-dimensional positioning system, which is composed of two 2-dimensional Infrared (IR) signal source trackers. Once the 2D trackers detect the incident angles of the IR signal source, the 3D positioning system will locate the IR signal source. In the experiments, the detection on the longitudinal direction is concerned, and the IR signal source on the preceding vehicle is detected by the 3D positioning system implemented on the following vehicle. While GPS cannot tell two adjacent vehicles, the short-ranged positioning system is able to locate the nearby moving target.