Typically with a width of 2m or less, transport in a VNA is very restrictive for MHE; therefore ground guidance systems are installed to expedite safe, controlled movement in the aisle, via wire or rail guidance.
Specialist MHE is required to operate in the narrow aisles, as they must be slender enough to move down the aisle (axle span of around 1.2m) and able to extend up to the top of the racking (up to 13m). Examples of MHE used in VNA include VNA trucks and stacker cranes.
Floor flatness is a key issue to consider in the construction of a VNA. For example, if a 5mm elevational difference across the 1.2m axle is considered, a static lean of 54mm is seen at the top of a 13m high racking. Considering also dynamic lean (x3-4 static lean), this could lead to 162mm sway causing potential collisions with the racking; carrying safety issues and limitations to the warehouse efficiency.