Carriers use the postal codes of the places of departure and destination to determine the distance the cargo must travel. They then use the weight and class of cargo - based on the NMFC codes established by the NMFTA (National Motor Freight Traffic Association) - to determine the cost of the shipment. Carriers also generally offer a discounted rate to customers who choose to consolidate their freight with other shippers. These discounts are usually granted by the carrier lowering the freight class of the items shipped, thereby reducing the price.