A method of transporting inventory items, comprising: a route planning module receiving a route request from a mobile drive unit, the route request identifying a destination location within a workspace, wherein the workspace comprises at least one cell associated with a first cell attribute and at least one cell that is not associated with the first cell attribute, the first cell attribute being associated with cells in which inventory holders are stored when not being transported, wherein the mobile drive unit, when not docked with an inventory holder, is able to move through spaces currently occupied by stored inventory holders but is not capable of doing so when docked with an inventory holder, the mobile drive unit comprising a docking head, the inventory holders each comprising a frame comprising a docking surface and four legs forming device openings to allow the mobile drive unit to move and position under the frame and adjacent to the docking surface, wherein the docking surface couples to a portion of the docking head when the mobile drive unit is docked with the inventory holder and supports the weight of the inventory holder while the inventory holder is docked with the mobile drive unit; the route planning module determining a state of the mobile drive unit; in response to determining that the mobile drive unit is associated with a first state, the route planning module generating a path to the destination location for the mobile drive unit that traverses cells associated with the first cell attribute, the first state being associated with a mobile drive unit that is not currently docked with an inventory holder; in response to determining the mobile drive unit is not associated with the first state, the route planning module generating a path to the destination location for the mobile drive unit that does not traverse cells associated with the first cell attribute; the route planning module transmitting a route response including information defining the generated path to the mobile drive unit; and after receiving the route response, the mobile drive unit beginning traversing the generated path to the destination location. a route planning module receiving a route request from a mobile drive unit, the route request identifying a destination location within a workspace, wherein the workspace comprises at least one cell associated with a first cell attribute and at least one cell that is not associated with the first cell attribute, the first cell attribute being associated with cells in which inventory holders are stored when not being transported, wherein the mobile drive unit, when not docked with an inventory holder, is able to move through spaces currently occupied by stored inventory holders but is not capable of doing so when docked with an inventory holder, the mobile drive unit comprising a docking head, the inventory holders each comprising a frame comprising a docking surface and four legs forming device openings to allow the mobile drive unit to move and position under the frame and adjacent to the docking surface, wherein the docking surface couples to a portion of the docking head when the mobile drive unit is docked with the inventory holder and supports the weight of the inventory holder while the inventory holder is docked with the mobile drive unit; the route planning module determining a state of the mobile drive unit; in response to determining that the mobile drive unit is associated with a first state, the route planning module generating a path to the destination location for the mobile drive unit that traverses cells associated with the first cell attribute, the first state being associated with a mobile drive unit that is not currently docked with an inventory holder; in response to determining the mobile drive unit is not associated with the first state, the route planning module generating a path to the destination location for the mobile drive unit that does not traverse cells associated with the first cell attribute; the route planning module transmitting a route response including information defining the generated path to the mobile drive unit; and after receiving the route response, the mobile drive unit beginning traversing the generated path to the destination location.