decide whether it is advisable to undertake the venture. If he experiences any difficulty in making up his mind as to the kinds of traffic for which he ought to provide, his engineer should be able to tell him approximately the cost of structure to carry any kind or combination of kinds thereof; and, knowing the probable receipts therefrom, he should then be able to come to a proper decision.

The question often arises as to whether it will pay to accommodate pedestrian travel; and, in the case of a long structure carrying street cars, it will not. In some cases, however, in order to procure a franchise for building the bridge, it may be necessary to agree to provide footwalks for pedestrians, even if there be very few of them. In the old days of horse-propelled vehicles, it was practicable for pedestrians to cross on the main roadway, but to-day the rapid passage of automobiles would render such a procedure exceedingly hazardous.

In the case of a proposed combined-railway-and-highway bridge, it is often good policy to floor over the railway deck so as to carry temporarily both trains and vehicles, and to provide for attaching brackets in the future to support the latter. Such an arrangement gives very poor service; but it often will suffice for a number of years.

In the building of a railway bridge only, the approaches may be timber trestles, which have a life of ten years, more or less; and at the end of that time they can be replaced either with new timber or by permanent construction. If the bridge be built to carry a double track, and if one track will take care of the traffic for a few years, a single track can be laid on the two inner lines of stringers, and the approaches may be single-track Wooden-trestles; or, if preferred, one side only of the double-track structure can be used, and the temporary approaches can be built off-center.

In ease of a great scarcity of funds, a double-track bridge can be designed with trusses for half live load and partial dead load, and an arrangement made in advance for the future doubling of trusses. The author evolved and patented this detail many years ago, but has never since had occasion to utilize it in actual construction, although he has estimated upon its employment.

Occasionally it is feasible to build a portion of the main bridge of permanent construction and the remainder of cheap, perishable materials; and this expedient, may be in the line of true economy. A quarter of a century ago the author built a bridge across the Missouri River between Council Bluffs, Iowa, and East Omaha, Nebraska, on the basis of part permanent and part temporary construction; and later he replaced the temporary portion with permanent spans. In the original structure the cheapening of everything was carried to the utmost legitimate, limit, in order to come within the bankers' appropriation. The pivot pier of the swing span (the largest in the world at that time, viz., 520 feet), was made permanent; but the span itself was stripped of its cantilever brackets for roadways and sidewalks, a portion of the deck was floored over for teams, a single track