LAVING OUT A RAILROAD.
The work of planning and laying out a railroad is something more than merely technical, since the question of the money that may safely be ex pended upon it, and consequently the character of its construction and ope ration, must be determined by the amount of traffic to be expected. The estimation of the probable passenger and freip.:lit traffic over a projected road is one of the most difficult of problems, demanding the closest inquiry into,. and consideration of, the existing local and through traffic of the dis trict, as well as the judicious valuation of the increased traffic which the new road may be expected to develop.
Classz:fication of Railroad Traffic.—ln the first place, the kind of traffic for which the road is designed to serve is the most important thing to con sider in planning it, and from this standpoint the following classification may be made: (1) Roads for the transportation of materials such as are used in mines, quarries, in the construction of public work-s, and the like: these are often provisional or temporary, and are commonly operated by horses or men; (2) Surface railroads in cities, designed for passenger traffic: these rarely employ the locomotive, the low speed and frequent stops re quired and the occurrence of abrupt curves on such roads rendering the ap plication of steam-power unsuited for this service, even were it not objec tionable for other substantial reasons; and (3) Elevated, depressed, and underground roads, operated by steam, for the rapid transfer of the popu lation of large cities: these roads are inet with on both sides of the Atlan tic. For the surface roads the electric motor and the cable-traction system have lately come into general nse in American cities as a substitute for animal traction.
Freight ana' Passenger Traffic.—The objects which the steam-railroad proper is intended to realize are the transporting of passengers with the greatest speed compatible with safety and the transporting of freight with the lowest possible cost. Up to the present time the division of these two classes of traffic has been made chiefly by separating the same in different trains (passenger and freight); upon many of the principal railroads, how ever, the separation of passeng-er and freight service is effected by the lay rim_ v.-12
int.; of additional tracks, of which certain lines are used exclusively for freight- and others for passenger-trains.
Main (Trunk) and Branch route of the main lines of rail roads will be determined by circumstances—for example, whether they are contemplated for countries with well-developed traffic and as the main stems or trunk-lines of a network of railroads covering the whole country, or whether they are contemplated for new or comparatively thinly-settled districts for the purpose of promoting the increase of their population and the development of their natural resources. While in the latter case the lines will be directed to those parts of the region whose products, etc. promise the most profitable returns, in the former the trunk-lines will be so located as to form the most direct connection between the important centres. Subordinate to the trunk-lines are those which may be designated as main lines of the second order, which serve as feeders to the trunk and as the means of supplying the industrial and commercial wants of localities of less importance; and subordinate to these, in turn, are the so-called branch or local roads, designed to transport and develop the local traffic of the districts contiguous to the main lines of the second order. The traffic upon these branch roads will consist mainly of crude products of the forest, mine, and farm, in the transportation of which the question of speed is of minor importance. The expense of laying out, constructing, and operating such local roads must be kept as low as possible. As the traffic of these roads increases, their capacity for handling the same must be correspond ingly increased by progressive improvements of road-bed, permanent way and general equipment, and additions to rolling-stock and motive-power. For reasons of economy, many roads of this class are constructed of nar rower gauge than the standard.