The need for new roads and trails depends upon the number of them already existing, the value of the resources that it is necessary to make accessible, the fire liability, and the amount of unrealized revenues due to lack of transportation facilities. If valuable grazing land or timber land can be made accessible there is good reason for building a new road. In many cases roads and trails are built to facilitate the protection of large remote areas from fire. Such areas may have large bodies of valuable timber which if destroyed by forest fires would involve a heavy loss. Even aside from valuable timber on an area, it is absolutely necessary when a forest fire breaks out to get to it with men and fire-fighting equipment in the shortest possible time before it spreads. If the fire gets to be a large one, many men with provisions, tents, fire-fighting tools, and other equipment must be transported to the scene of the fire. Any delay in the transportation of these things may prove fatal and may result in an uncontrollable conflagration. The transportation system that is proposed for a National Forest, if the one that exists is inadequate, is usually planned many years ahead. The ultimate or ideal system is always kept in mind so that every mile of road or trail that is constructed is made a part of it. If not enough money is available for a good road, a trail is built along the line of the proposed road. Later this trail is widened into a permanent road. The Engineer connected with each District Office usually has charge of laying out big road projects. A few miles of permanent, good, dirt road with good grade is always preferred to many miles of poor road with heavy grade and improper drainage. A road and trail system is planned for each National Forest which will eventually place every portion of the Forest within a distance of at least 7-1/2 miles of a wagon road. A pack-train can then transport supplies from the point to which they are delivered on the wagon road to any field camp and return in a single day. In trail and road construction it is very often necessary to build bridges. Sometimes a very simple log bridge meets the need, but in bridging many large mountain torrents, which become very high and dangerous in the spring, large bridges are necessary. Cable suspension bridges and queen and king truss bridges are built where occasion arises for them, but only after being planned in detail and after the District Forester has approved their design and method of construction. [Illustration: Figure 14. A typical Forest ranger's headquarters. Idlewood Ranger Station, Arapaho National Forest, Colorado]