There is an economic question concerning embankments, not at all difficult to settle, which exists when the right-of-way is expensive; and that is whether it is preferable to use wide banks with the natural side-slopes or to build concrete side-walls and thus diminish the area to be occupied. The only proper way to determine the economics in this case is to make a complete estimate of cost for each layout, based upon current prices of materials, labor, and right-of-way.

Occasionally in an engineer's practice there arises the economic question whether it will be better to build an expensive abutment with wing-walls, and possibly also toe-walls, or an inexpensive buried pier with longer superstructure and with rip-rap protection along the end and sides of the embankment. In most cases the latter will prove the more economic, but that such is the case should never be assumed without making accurate comparative estimates. With substantial bank protection that no flood is likely to wash out, the expedient of the buried pier is a perfectly legitimate one, and the construction involved by its use can properly be deemed first-class.

The choice between a steel trestle and a reinforced-concrete trestle for an approach should always be determined by including in the comparing estimates of cost the equivalents for depreciation, maintenance and repairs, giving a substantial preference to the concrete layout because of the possibility of future deterioration of the steel due to neglect of painting.

As indicated on page 1193 of "Bridge Engineering" there are given in Chapters 53, 55, and 56 of that treatise a large number of tables and diagrams, by means of which can be quickly computed the costs of the embankments, timber trestles, steel viaducts, reinforced-concrete viaducts, retaining walls, abutments, and culverts which may be needed in estimating the cost of approaches to bridges. From these data there can also be found very easily the comparative economics of plain and reinforced concrete for building retaining walls and abutments.

It is sometimes the case that in the approaches to a proposed bridge there would be a variation in the total cost of right-of-way and property damages by adopting different kinds of construction therefor, hence this matter should always receive due consideration. One of the most effective methods of economizing on these items is to substitute a spiral approach, such as mentioned on page 1076 of "Bridge Engineering," for the usual straight trestle. While the construction costs of the two types do not differ materially, if the property occupied or damaged be very valuable, a great saving can sometimes be secured because of the comparatively small and compact area required for the spiral. Moreover, it is sometimes practicable to construct a building in connection with the latter, that will bring in such large rentals as more than to wipe out all costs for right-of-way and property damages.

In general, it may be stated that timber trestle is the cheapest kind of approach, as far as first cost is concerned, excepting for small heights, but