1. A computer-implemented method of controlling the motion of an autonomous vehicle, comprising: obtaining, by one or more computing devices on-board an autonomous vehicle, data associated with one or more objects that are proximate to the autonomous vehicle, wherein the data comprises a predicted path of each respective object; identifying, by the one or more computing devices, at least one object as an object of interest based at least in part on the data associated with the object of interest; generating, by the one or more computing devices, cost data associated with the object of interest, wherein the cost data is indicative of an effect of controlling a motion of the autonomous vehicle such that the autonomous vehicle travels behind or in front of the object of interest in a manner that corresponds to a motion of the object of interest; determining, by the one or more computing devices, a motion plan for the autonomous vehicle based at least in part on the cost data associated with the object of interest; and providing, by the one or more computing devices, data indicative of the motion plan to one or more vehicle control systems to implement the motion plan for the autonomous vehicle.