The determination of the best possible layout for any proposed structure is truly an economic problem, notwithstanding the fact that many of the considerations which influence it may not bear directly on the question of cost. It is one of the most important responsibilities in the province of the bridge engineer, and to do the work in the most effective manner possible demands a wide experience, coupled with good judgment and the ability to foresee eventualities over a long period of years. The general idea that the best possible layout is the one which makes the first cost of structure a minimum is a fallacy; for there are many other considerations besides economy in initial expenditure that are of great importance. The following is a fairly complete list of the various items which should be carefully considered before settling finally upon the layout of grades, clearances, span-lengths, character of substructure, and type of superstructure to adopt. This is a long list, but it must be remembered that it is intended to cover all the considerations for all cases, and that, probably, only a few of the items will apply to any particular case.

List of Factors and Conditions Affecting the Layouts of Bridges

While there is an attempt at logic in the arrangement of the preceding list on the combined lines of natural sequence and comparative importance, it is impossible to state in advance for any particular case or class of cases which are the items that should receive the most consideration. Each item will be taken up and discussed in the order adopted in the list.

Government Requirements

In Chapter L of "Bridge Engineering" the requirements of the United States Government regulating the bridging of navigable streams are treated

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