A controller arranged to control movement of a plurality of transporting devices, the plurality of transporting devices arranged to transport containers, the containers being stored in a facility, the facility arranged to store the containers in a plurality of stacks, the facility comprising a plurality of pathways arranged in cells so as to form a grid-like structure above the stacks, wherein the grid-like structure extends in a first direction and in a second direction, the plurality of transporting devices arranged to operate on the grid-like structure, the controller comprising: a route determination unit arranged to determine a route from one location on the grid-like structure to another location on the grid-like structure for each transporting device; a clearance unit arranged to provide clearance for each transporting device to traverse a portion of the determined route; a constraint area determination unit arranged to determine a plurality of constraint areas based on the grid-like structure; and a calculation unit arranged to calculate a constraint limit in each constraint area, wherein at least one of: the clearance unit is further arranged to grant or withhold clearance to a transporting device to traverse a portion of the determined route based on the calculated constraint limit in the particular constraint area, and the route determination unit is further arranged to determine a route for a transporting device from one location to another location traversing or not traversing a particular constraint area based on the calculated constraint limit in the particular constraint area, characterised in that the constraint area determination unit is arranged to determine constraint areas based on a structural analysis and/or fatigue analysis of at least one of the grid-like structure, any mezzanines associated with the grid-like structure, or any peripherals associated with the grid-like structure. a route determination unit arranged to determine a route from one location on the grid-like structure to another location on the grid-like structure for each transporting device; a clearance unit arranged to provide clearance for each transporting device to traverse a portion of the determined route; a constraint area determination unit arranged to determine a plurality of constraint areas based on the grid-like structure; and a calculation unit arranged to calculate a constraint limit in each constraint area, wherein at least one of: the clearance unit is further arranged to grant or withhold clearance to a transporting device to traverse a portion of the determined route based on the calculated constraint limit in the particular constraint area, and the route determination unit is further arranged to determine a route for a transporting device from one location to another location traversing or not traversing a particular constraint area based on the calculated constraint limit in the particular constraint area, the clearance unit is further arranged to grant or withhold clearance to a transporting device to traverse a portion of the determined route based on the calculated constraint limit in the particular constraint area, and the route determination unit is further arranged to determine a route for a transporting device from one location to another location traversing or not traversing a particular constraint area based on the calculated constraint limit in the particular constraint area, characterised in that the constraint area determination unit is arranged to determine constraint areas based on a structural analysis and/or fatigue analysis of at least one of the grid-like structure, any mezzanines associated with the grid-like structure, or any peripherals associated with the grid-like structure. <EOS>