The actual cost of a tie equals the total of several items, of which the first cost is but one item. It must be transported from the place of sale and delivery to the road to the place where it is to be used. A certain amount of, track-labor is necessary to place the tie in the track. A considerable amount of track-labor is necessary to maintain the track at a proper surface. The amount of this labor will depend considerably on the length, width and weight of the tie, since a large heavy tie has such a hold in the ballast that it is not so easily disturbed by the passage of trains. Since the cost of track-labor is such a very important item in the total cost of a tie, a tie which can be kept in the track for a greater length of time and with less work for maintenance may be far more economical in the long run than a tie which has cost less money. The annual cost of a system of ties may be considered as the sum of (a) the interest on the first cost, (b) the annual sinking-fund that would buy a new tie at the end of its life, and (c) the average annual cost of maintenance for the life of the tie which includes the cost of laying and the considerable amount of subsequent tamping that must be done until the tie is fairly settled in the road-bed. The following very conservative estimate of the relative cost of untreated ties and ties which have been treated chemically is given as follows: the cost of the untreated tie is estimated at 40 c, while the cost of the chemical treatment is assumed to be 25 c., making the total cost of the treated tie 65 c. The life of the untreated tie is assumed to be seven years and that of the treated tie fourteen years. The annual interest on the first cost estimated at 4% will therefore be 1.6 and 2.6 c. respectively. The sinking-fund at 4% which would renew each tie at the given cost at the end of its estimated life will be 5.1 and 3.6 c. respectively. The average annual cost of maintenance is very difficult to estimate, but, since we are seeking a comparison rather than a definite estimate of cost, all that we need to know is the excess of the cost of one method of construction over the other. Owing to the impracticability of giving a definite figure for item (c) we will assume that it balances for the two methods, but with the understanding that the advantage is very distinctly with the treated tie and that the advantage extends not only to the comparative cost of track-work but also the indefinite saving in operating expenses, due to less jar of the rolling-stock on a smoother track, less cost of repairs, less consumption of energy by the locomotive, and all the advantages of a smoother track. Collecting these items we have the tabulated form as follows:
Original cost ............
40 cents 7 years
Life (assumed at) ..................
Item (a) - interest on first cost at 4%
" (b) - sinking-fund at 4%...............
" (c) - (considered here as balanced) ....
Average annual cost (except item (c)) ............
The methods of chemical treatment of ties will not be here discussed, as they may be found in numerous text-books. It is not easy to obtain an accurate estimate of the effect of chemical treatment, unless reliable figures showing the total life in the track of a very large number of ties are obtainable. It frequently happens that, owing to some imperfection in the tie or some error in its treatment, a treated tie may not last even as long as a wooden untreated tie. It is only by obtaining the average figures for a very large number of ties (at least several thousand) that a true measure of the economy of chemical treatment can be obtained. The lack of accurate figures is due largely to the fact that it is practically a difficult matter to keep track of the actual life of the ties. Chalk-marks, and even numbers stamped with dies, are easily obliterated in a few years. Marking the ties with tacks arranged to form letters seems to be the best method, and it has therefore been largely adopted by railroads which have determinedly made a study of this question. But such a method involves trouble and work which few roads have been willing to make. Even when figures have been obtained regarding the life of ties, it will be found that, of a lot of ties which are supposed to be uniform and whose average life is supposed to be say seven years, a considerable percentage of the ties may need to be removed in two or three years, while a very considerable percentage of them may still be in the track after 12 or 15 years' service. Similar figures are found for the life of chemically treated ties, some of them requiring removal after a very few years' service, while others will last much longer than could be claimed by the promoters of that particular system of tie treatment. It therefore becomes necessary in comparing the life of untreated ties with treated ties, or in comparing the life of ties treated with different methods of treatment, to compare the percentages of removals after a given period of years. It practically amounts to the same thing to determine for each kind of tie or each method of treatment a curve, showing the number of ties as one set of ordinates, and their corresponding life for the other. The comparison of such curves will show which manner of treatment gives the best results.