This paper focuses on development of an active sensing system for a bicycle to accurately track rear vehicles. Cost, size and power constraints highly limit the type of sensor that can be used on a bicycle for measurement of distances to vehicles. A single beam laser sensor mounted on a rotationally controlled platform is proposed for this sensing mission. The rotational orientation of the laser sensor needs to be controlled in realtime in order to focus on a target point on the vehicle, as the vehicle's lateral and longitudinal distances change. This tracking problem involves two challenges: Controlling the real-time angular position of the laser sensor based on very limited information and tracking the vehicle's position for different types of maneuvers. The first challenge is addressed by developing an algorithm to detect whether a reflection is from the front or side of the target vehicle and then controlling sensor orientation to alternately obtain both lateral and longitudinal distance measurements. The second challenge is addressed by using an interacting multiple model observer that incorporates straight and turning vehicle motion models. Simulation results are presented to show the advantages of the developed tracking control system compared to simpler alternatives.