1. A computer-implemented method for tracking vehicles that are perceived by an autonomous vehicle, the method comprising: obtaining, by one or more computing devices included in the autonomous vehicle, state data descriptive of a previous state of a tracked vehicle that is perceived by the autonomous vehicle, wherein the previous state of the tracked vehicle comprises at least one previous location of the tracked vehicle or a vehicle bounding shape associated with the tracked vehicle; predicting, by the one or more computing devices, one or more first locations for a first vertex or a first side of the vehicle bounding shape based at least in part on the state data; obtaining, by the one or more computing devices, observation data descriptive of one or more sensor observations; determining, by the one or more computing devices, a second location of a second vertex or a second side of an observation bounding shape associated with the tracked vehicle based at least in part on the observation data; and determining, by the one or more computing devices, at least one estimated current location of the first vertex or the first side of the vehicle bounding shape associated with the tracked vehicle based at least in part on a comparison of the one or more first locations for the first vertex or the first side of the vehicle bounding shape to the second location of the second vertex or the second side of the observation bounding shape.