<P> Railroads saw their greatest growth in new track added in the last three decades of the 19th century . (See Table 2) Railroads also enjoyed high productivity growth during this time, mainly because of the introduction of new processes that made steel inexpensive . Steel rails lasted roughly ten times longer than iron rails . Steel rails, which became heavier as steel prices fell, enabled heavier, more powerful locomotives that could pull longer trains . Rail cars made of steel on steel roads could be made longer cars and had a load carrying to car weight ratio of 2: 1 compared to cars made of iron at 1: 1 . </P> <P> In 1890 David Ames Wells estimated wagon transport at 16 cents per ton - mile compared to railroads at less than one cent per ton - mile . </P> <P> Railroads competed fiercely for passengers and freight by expanding their routes, too often into increasingly marginal ones . The high capital required for expansion plus the low rates, driven by competition and by what the market would bear, resulted in a large percentage of railroad track in bankruptcy . </P> <P> A practical refrigerated (ice cooled) railcar was introduced in 1881 . This made it possible to ship cattle and hog carcasses, which weighed only 40% as much as live animals . Gustavus Franklin Swift developed an integrated network of cattle procurement, slaughtering, meat - packing and shipping meat to market . Up to that time cattle were driven great distances to railroad shipping points, causing the cattle to lose considerable weight . Swift developed a large business, which grew in size with the entry of several competitors . </P>

Most of the u.s. economic growth between 1790 and 1860 was caused by