A warehouse consists of 5aisles of racks (racks on both sides of each aisle) and a loading dock. Forklift trucks are used to transport loads between the loading dock and the storage compartments of the rack system in each aisle. Trucks move at an average speed of 140 m/min loaded and 180m/min empty.

Load handling time (loading plus unloading) per delivery totals 1 min per storage/retrieval. Traffic factor is 0.9, worker efficiency is 100% and reliability/availability is 96%.

The average distance between the dock and the centre of the aisles are 200, 300, 400, 500 & 600 meters. Suppose the warehouse is organised into a class based storage strategy on activity level of the pallet loads in storage, so that aisles 1 & 2 accounted for 70% of the deliveries (Class A) and aisles 3,4 and 5 accounted for the remaining 30% (Class B).

Assume that the deliveries in Class A are evenly divided between aisles 1 & 2 as are those in Class B between aisles 3, 4 & 5.

How many trucks would be required to achieve 100 storage/retrieval deliveries per hour?