These examples might be continued so as to include the finding of quantities in retaining walls, both plain and reinforced, reinforced-concrete trestles, and reinforced-concrete arch bridges, but space will not permit; hence the reader is referred for examples of the estimates for such structures to pages 1317-1347 of "Bridge Engineering."

Again, by employing the various formulae given in Chapter XXVII of that treatise, the cost of any highway or electric railway suspension bridge can be quickly estimated. As stated elsewhere herein, the author in a single working day made thereby a close estimate of cost for a 2,500' span, highway bridge, including substructure, superstructure, approaches, and accessory works, for a proposed crossing of the Detroit River at the City of Detroit.

The eleven simple examples given should suffice to illustrate the facility with which one who is familiar with "Bridge Engineering" can figure the quantities of materials for all ordinary bridges. Those for other structures can be obtained in a similar manner by the expenditure of somewhat more time, but still very readily.

The following are the four student problems referred to near the beginning of this chapter; and the author again suggests that they be solved by any young engineer who desires to perfect himself in the art of making quick computations for costs of bridges:

Problem A

The following data for a river crossing are supposed to be furnished by a survey for a double-track, steam railway in the northwest corner of the state of Arkansas: