1. A system, comprising: an autonomous vehicle, including: a stuck-condition detection component, configured to detect a condition in which the autonomous vehicle is impeded from navigating according to a first trajectory, and a communications component, configured at least to send an assistance signal indicating that the autonomous vehicle seeks assistance navigating according to the first trajectory, and to receive a response to the assistance signal, wherein the assistance signal includes sensor information of the autonomous vehicle, indicating low-level sensor strike input and high-level, polygonal or polyhedral representations of objects in the vicinity of the autonomous vehicle; and an assistance center, including: a communications component, configured at least to receive the assistance signal, and to send the response to the assistance signal, and a trajectory specification component, configured to specify a second trajectory for the autonomous vehicle, and to generate the response to the assistance signal including a representation of the second trajectory, wherein the second trajectory is based on the first trajectory, and wherein the second trajectory ignores the presence of at least one high-level, polygonal or polyhedral representation of an object that obstructs the first trajectory.