Item 61 unaffected. Items 62 to 76, station and yard expenses, will be considerably affected because the number of trains is increased, even though the number of freight cars is identical. An average increase of 50% for the extra train may be allowed for these items. Although the wages of road enginemen (Item 80) vary somewhat with the tonnage of the locomotives, they do not vary in strict proportion to it. Some schedules of wages pay no attention to the weights of locomotives, but only consider the class of service, whether passenger service, through-freight, or local freight. In such cases the amount paid in wages would be strictly according to the number of engines. In other cases there is an addition of 5 to 10% paid for handling the heavier engines. Assuming an average of 8% increase, we would have for four light engines 400% and for three heavy engines 324%, or an addition of 76% of the average wages for one engine, as the result of using the additional engine. Of course this item will vary with each particular case. The relative cost of fuel consumption with the heavier engines depends very largely on the particular engines compared. It is not unknown that a considerably heavier engine of one type may actually burn less fuel than a lighter engine of another type and make. When we consider the very large amount of fuel which goes to waste by radiation, the amount which is consumed when an engine is doing very little or no work, as when it is running on a level or on a down grade, and the proportion which is consumed in various other ways, as has already been described, it may readily be seen that only a small proportion of the fuel used may be considered as proportionate to its tonnage or proportionate to the weight on the drivers. The late A. M. Wellington considered that 75% of the fuel used would be unaffected by the weight of the engine, and that only the remaining 25% would be affected according to the tonnage. We might therefore express the amount of fuel used by four light engines as 4X75% + 4X25% = 400%.
The cost of operating three heavy engines may be expressed as 3x75% + 3(4/3X25%)=325%.
Therefore the added cost of fuel for the one lighter engine would be 75% of the average figure for one. We will consider that the other engine-supplies are affected similarly, and we therefore allow 75% for Items 81-85. The number of trainmen required for each train will not be affected by cutting off a few cars and we must therefore add the full amount for Item 88, Road trainmen. Since Item 89 applies only to cars, and chiefly to passenger-cars (see § 68), and the number of cars is unchanged, there will be no extra charge for Item 89. The remaining items (90 to 103) are small but will be charged at full train value, 100%. The debit and credit items, 104 and 105 (and also 77 and 78) nearly balance and in this, and all other similar computations, will be considered as unaffected. If we multiply each percentage, as given in Table IX, by the corresponding percentages which have been computed above for each item, the summation of these products will be the percentage of the average cost of a train-mile, which will be an estimate of the cost of the assumed condition. If we multiply this by the average actual cost of a train-mile we will have an estimate of the cost of one mile of this sort of operation. It is a question whether we should take the average figures for the year 1910, or, perhaps, even a still higher figure.