Abstract? In this paper, a dedicated on-board `sensor' utilizing wireless communication devices was developed for the collision avoidance around intersection. Four ZigBee wireless receivers are installed in the four corners of the driver's vehicle. Each receiver is shielded and has slightly directivity. These setting enable `sensor' to estimate the positions of the transmitters on pedestrians, bicycles, motor cycles, and vehicles based on a comparison of four signal strengths received from the four receivers. Since the estimation algorithm considers relative values obtained from the four wireless receivers, the detection results should not be affected by the transmission power. In addition to this, we improved our previous work considering the ground reflection model. On-board sensors utilizing vision, Laser Imaging Detection and Ranging (LIDAR), and radar cannot detect objects hidden by road facilities and other vehicles. Although infrastructure sensors for vehicle-to-infrastructure (V2I) cooperative systems can detect such hidden objects, they are substantially more expensive than on-board sensors. The on-board wireless `sensor' developed in this work would function as an alternative tool for collision avoidance around intersections.