13% Modern Business Geography United States Bureau of Mines. Fic. 132. Here mineral resources have attracted a railroad. few inches. This makes the road very rough and dangerous, and also adds greatly to the expense of keeping it up. (4) Double tracks and sidings. Some roads must have two tracks, and all must have frequent sidings where trains can pass one another. Among mountains it is often very expensive to blast out a space even for a siding. Nevertheless, the sidings must be frequent, for they determine how many trains can run per day on all single track roads. If it takes an hour for a train to go from one siding to the next, only twelve trains per day can run in each direction. (5) Stations and freight yards. Another great expense to railroads is the building and maintaining of stations and freight yards. As a town grows, it wants a new and better looking station; the manufac- turers and merchants want more tracks and freight houses in the freight yard; and those who are not near the yards want spur tracks to their places of business. It is wise for the railroad to spend money for such purposes, but it costs a great deal. (6) New equipment. Finally, not only does almost everything that is used on a railroad grow old and wear out, but new inventions and improvements demand large expenditures. For instance, when steel cars were invented people began to complain that wooden cars were not safe and to demand that the railroads replace them with steel cars. The invention of the block signal system led to another large item of expense, which will continue until all railroads are fully