Traffic on the U.S. rail network continues to weaken in a sign of the slowdown spreading across the industrial economy and efforts by firms to reverse the unplanned build up of inventories throughout the supply chain. The number of railcars and containers carried by the major railroads was down 8 percent last week compared with the same week a year earlier, according to the Association of American Railroads (AAR). For the first 49 weeks of 2015, traffic has fallen 2.1 percent compared with the same period in 2014. At the end of June, rail traffic was down just 0.9 percent year on year, according to the AAR. The slowdown in the industrial economy has deepened, with carloads carrying bulk commodities down 3.8 percent in the first half of the year, down 5.4 percent in the year to date, and down 13.2 percent year on year last week. In the second half of 2015, the slowdown has spread to the more high-value and consumer side, with container shipments growing 2.3 percent in the first six months, but just 1.7 percent for the year to date, and actually down 2.3 percent in the most recent week. The weakness is rail shipments has been matched by sluggishness in other forms of freight transportation over the last 12 months  Freight volumes carried by road, rail, barge and pipeline peaked in November 2014 and have been essentially flat since then, ending five years of strong growth, according to the U.S. Bureau of Transportation Statistics. Some of the weakness is the result of the end of the oil boom, which has cut the amount of crude shipped by rail, and had a knock-on effect on shipments of everything from drill pipe to fracking sand. Coal shipments, which are the largest single item on the rail network, have been hit hard as lower natural gas prices and environmental regulations encourage power producers to switch to burning gas. But the weakness extends to most other industrial and forest products and more recently it has spread to containerised shipments of consumer products. Rail shipments were down compared with 2014 in 11 out of 13 categories last week and in 5 out of 11 categories for the year to date, according to the AAR. Manufacturers, distributors and retailers are all struggling to reverse the unplanned increase in inventories over the last 12 months The ratio of inventories to sales at all stages in the supply chain has increased steadily from 1.31 in October 2014 to 1.38 in October 2015, according to the U.S. Census Bureau. The inventory/sales ratio for manufacturers has risen from 1.32 to 1.35, while retailers are up from 1.43 to 1.48 and wholesalers are up from 1.22 to 1.31. Retailers report higher stocks of everything from building materials and garden equipment to clothing and general merchandise. Unusually warm weather throughout autumn and the start of winter is likely to depress sales of seasonal clothing which will leave retailers struggling even longer to clear shelves and warehouses. Concerted efforts to reduce the level of unwanted inventories have hit new orders and shipments across the entire manufacturing sector. The major exception is auto manufacturing, where sales of light duty vehicles, especially crossover utility vehicles and sport utility vehicles, are on course to hit a record. But with the ratio of inventories to sales still rising as recently as October, destocking efforts are likely to continue for at least the next several months, depressing freight growth into the start of 2016.