The idea of cost of reproduction is not synonymous with the idea of the cost of building a railway capable of serving the same transportation purpose. If all our railways were to be built anew, in the light of our present knowledge, and with our present traffic offerings and financial resources, vast changes would be made in the character of construction. The physical fact of existing construction prevents a theoretical substitution of what is the best construction for any community, together with its costs for the construction which was actually made years ago. In the event that an estimate of reproduction costs be made for a State as a whole, or for a great railway system as a whole, the conception of reproduction is modified so that the construction may take the form of progressive construction, the principal lines being built first and the less important lines afterward. This method will require the estimate for interest during the construction period to be greater. The money cost of the seasoning and the adaptation of the roadway to such a condition as will permit heavy trains to be run at high speeds, is great, but the amount is not readily ascertained. An estimate of cost of reproduction, to be true, must consider this item; and probably the more usual method of ascertaining it is to assume it to be an amount in some proportion to the cost of the excavation. This proportion will vary with the character of the material through which and of which the cuts and fills are made, and with the methods of construction necessarily adopted. There are many railways on which this cost will exceed 25% of the total cost of excavation. After the estimate has been made, including the item for seasoning and adaptation, there should be added a contingent fund to cover the omitted work, consisting of small borrow-pits and ditches, undetermined foundations, unexpected conditions encountered, unavoidable "force account" work, minor changes of streams and highways, damages to adjoining lands due to the methods of construction and to diversion of water, etc. This item will not exceed 5% of the cost of the roadway if the estimate be accurately made. The more convenient form into which an estimate of cost of reproduction of a steam railway is to be put is to follow the sub-accounts, as prescribed by the Interstate Commerce Commission for Expenditure for Road. Each item given in that accounting has a place in the estimate. These comments are confined to the items covering the roadway, namely, Right of Way and Station Grounds, Grading, Tunneling, Bridges, Trestles, and Culverts.