There are two basic floor categories: random traffic and defined traffic. Currently, fewer than 1% of the floors constructed in the US are classified as defined traffic. In very-narrow-aisle warehouses, forklifts travel 6-foot wide aisles between storage racks with the aid of rack-mounted rails or a wire guidance system embedded in the floor. While moving down the aisles, these lift trucks can raise their forks to retrieve or place products at various levels. For these forklifts to perform as intended, defined-traffic floors must be extraordinarily flat and level, or superflat.