As is indicated by Table VII and Fig. 6, the average cost per train-mile seems to be steadily increasing, while certain of the percentages of the items of cost seem to be regularly increasing (or diminishing) instead of merely fluctuating. On this account the averages for the year 1910 will probably be incorrect as an estimate for immediate future costs. These percentages have been combined in Table XII, page 143. If we assume that the average cost of a train-mile is \$1.50, then the operating value of saving the use of the additional engine equals 33% of \$1.50 or 50 c. There is, however, one additional item to be considered. Although Items 25-27 includes repairs and renewals of locomotives, it does not include the addition, if any, for the capital cost of the extra locomotive. Perhaps this extra cost may be zero. If we consider that the cost of locomotives is roughly proportional to their tonnage, and that, with locomotives of the same type, the tractive force is nearly proportional to their tonnage, then the four locomotives would cost no more than the three heavier locomotives of equal power. But if the four locomotives cost somewhat more (as is probable), then the extra cost, say \$2000, divided by the mileage life of the locomotive, say 800,000 miles, would require 0.25 c. to be charged to the above cost per mile. In this case the addition is almost too small for consideration, but in other cases it should not be neglected.

## Table XII. Additional Cost Of Operating A Given Freight Tonnage With (N+1) Light Engines Instead Of N Heavier Engines

 No. Item (abbreviated). Normal average, per cent. Per cent affected. Cost per cent. 1-23 Maintenance of way and structures. 20.09 0 0 24 Supt. of equipment.............. 0.64 0 0 25-27 Repairs, etc., locomotives........ 8.62 0 0 28-30 Electric locomotives........... 0.01 0 0 31-33 Passenger cars ............... 2.14 0 0 34-36 Repairs, etc., freight cars......... 10.15 -10% -1.01 37-52 Other equipment ................ 1.18 0 0 Maintenance of equipment...... 22.74 .......... -1.01 53-60 Traffic......................... 3.08 0 0 61 Supt. of transportation........... 1.20 0 0 62-76 Dispatching, station and yard expenses ....................... 16.25 50% 8.12 77-79 Dr. and Cr.; also elec. motormen. . 0.47 0 0 80 Road enginemen................ 6.08 76% 4.62 81-85 Enginehouse; fuel and supplies.... 13.13 75% 9.85 86-87 Electric power .............. 0.06 0 0 88 Road trainmen.................. 6.40 100% 6.40 89 Train supplies.........'......... 1.78 0 0 90-103 Signaling; loss and damage, etc... 5.05 100% 5.05 104-105 Dr. and Cr. - joint facilities....... 0.02 0 0 Transportation ............ 50.44 ......... 34.04 106-116 General expenses................ 3.65 0 0 100.00 .................. 33.03