Traditional warehouses use parallel picking aisles meeting cross-aisles at right angles. Non-traditional designs break the right-angle rule by adding diagonal cross-aisles or angling the picking aisles, shortening the path between storage locations and a single pickup/deposit (P&D) point. For unit-load operations served from one depot, this cuts travel measurably.
The two canonical designs (Gue & Meller 2009)
Gue & Meller (2009, IIE Transactions 41(3):171-182; DOI: 10.1080/07408170802112726) introduced two designs that beat the traditional layout for single-command unit-load travel:
Flying-V. Keeps picking aisles vertical but bends the cross-aisles into a shallow V aimed at the P&D point, giving a more direct diagonal path to distant locations. Modest savings, minimal disruption to a conventional rack grid.
Fishbone. Splits the floor into regions around a central diagonal cross-aisle (the spine) with angled picking aisles branching off it like ribs. Every location has a near-straight shot to the central P&D point. The stronger of the two designs.
Travel savings: the fishbone reduces expected single-command travel by roughly 10 to 20% versus a traditional layout; the flying-V less (Gue & Meller 2009). Bortolini et al. (2020, DOI: 10.1007/s00170-020-06235-4) report about 11 to 17% integrating single and dual command.
Where the savings come from, and where they go
The gain is geometric and depends on three conditions:
- A single P&D point. The diagonals aim at one depot. With multiple docks spread along a wall, the benefit erodes.
- Single-command (or near-single-command) cycles. Best for store-one or retrieve-one trips to and from the depot, the unit-load and AS/RS pattern. For dual-command, and especially multi-stop human picking, the diagonal geometry helps less and can hurt, because a many-stop route does not radiate from one point. Pohl, Meller & Gue (2009, DOI: 10.1002/nav.20355) quantify the dual-command case; the advantage shrinks.
- Velocity-based storage. Combine the layout with class-based slotting (fast movers near the spine) to compound the gain.
The cost: angled aisles waste some floor at the building corners, and racking, sprinkler, and column grids are harder to fit to non-orthogonal aisles. Net storage density typically drops a few percent, traded for the travel savings. Layout and control policy should be optimized together, not in sequence (Roodbergen, Vis & Taylor 2015, DOI: 10.1080/00207543.2014.978029).
Interaction with AGV and AMR navigation
The fishbone and flying-V results were derived for human or generic single-command vehicles. They do not model the navigation and traffic constraints of automated vehicles, which is where the practical question lives.
- Fixed-path AGVs (wire or magnetic-tape guidance): the guide path must run along the diagonals, and the spine creates acute-angle junctions. Acute-angle turns can exceed a fixed-path AGV’s turning radius, forcing wider aisles that erode the travel and density gains. Diagonal multi-way intersections also complicate zone reservation and deadlock avoidance versus a clean orthogonal grid. See AGV Traffic and Aisle Design.
- Free-navigation AMRs (SLAM or natural-feature): these need no physical guide path and route over arbitrary geometry, so they realize the fishbone benefit far better than legacy AGVs. The diagonal layout becomes a routing input, not a navigation obstacle.
- AS/RS and unit-load shuttles: a single-P&D, single-command pattern is exactly what the fishbone optimizes, so non-traditional layouts map cleanly onto crane and shuttle unit-load systems feeding one I/O point. See AS-RS Sizing Methods.
Bottom line: non-traditional layouts pay off most for single-P&D unit-load flows and for free-navigation AMRs. For fixed-path AGV fleets or dense multi-stop picking, model the turning and traffic penalty in simulation before committing. The academic literature does not yet quantify the fishbone-plus-AGV-traffic interaction, so this is a validate-by-DES decision, not a published-benchmark one.
When to use
| Situation | Fit |
|---|---|
| Unit-load, single P&D point, single/dual command (AS/RS, unit-load AGV) | Strong: fishbone |
| Free-navigation AMR fleet, single depot | Strong |
| Conventional racking, want a low-disruption tweak | Flying-V |
| Multi-stop human order picking, many tours per shift | Weak: diagonal geometry helps little, can hurt |
| Fixed-path (guide-wire) AGV fleet | Caution: turning and traffic penalty may erase the gain; simulate first |
| Multiple docks spread along the building | Weak: no single point for the diagonals to target |
See Facility Layout Design for overall layout method and AS-RS Sizing Methods for the single-versus-dual command cycle math the savings build on.