A computer-implemented method of operating an autonomous vehicle to change from a source lane to a target lane, the method comprising: selecting a first reference node of a topological graph associated with the source lane, the first reference node being a node in the source lane at which the autonomous vehicle can change to a second reference node in the target lane; determining, with respect to the first reference node of the topological graph, an earliest node in the source lane at which it is first possible for the autonomous vehicle to change lanes from the source lane to the target lane; determining, with respect to the first reference node of the topological graph, a last node in the source lane after which it is no longer possible for the autonomous vehicle to change lanes from the source lane to the target lane; and determining a range of the source lane for which the autonomous vehicle can change from the source lane to the target lane, wherein the range is from the earliest node in the source lane to the last node in the source lane, characterized in that determining the last node comprises: performing a conditional breadth-first search for nodes in the source lane after the first reference node until a node in the source lane is found that does not have a corresponding node in the target lane, the corresponding node in the target lane being a node at which the autonomous vehicle can change from the node in the source lane to the node in the target lane, wherein segments of the source lane are merged between the first reference node in the source lane and the last node. selecting a first reference node of a topological graph associated with the source lane, the first reference node being a node in the source lane at which the autonomous vehicle can change to a second reference node in the target lane; determining, with respect to the first reference node of the topological graph, an earliest node in the source lane at which it is first possible for the autonomous vehicle to change lanes from the source lane to the target lane; determining, with respect to the first reference node of the topological graph, a last node in the source lane after which it is no longer possible for the autonomous vehicle to change lanes from the source lane to the target lane; and determining a range of the source lane for which the autonomous vehicle can change from the source lane to the target lane, wherein the range is from the earliest node in the source lane to the last node in the source lane, characterized in that determining the last node comprises: performing a conditional breadth-first search for nodes in the source lane after the first reference node until a node in the source lane is found that does not have a corresponding node in the target lane, the corresponding node in the target lane being a node at which the autonomous vehicle can change from the node in the source lane to the node in the target lane, wherein segments of the source lane are merged between the first reference node in the source lane and the last node. performing a conditional breadth-first search for nodes in the source lane after the first reference node until a node in the source lane is found that does not have a corresponding node in the target lane, the corresponding node in the target lane being a node at which the autonomous vehicle can change from the node in the source lane to the node in the target lane, wherein segments of the source lane are merged between the first reference node in the source lane and the last node.