The actual mileage traveled by pusher-engines for each train assisted must be something in excess of twice the distance between the sidings at the top and bottom of the grade. Usually a telegraphic station at both the top and the bottom of the grade is at least very convenient if not essential to safe and efficient operation. If a regular stopping-place of the road is located even a mile or two beyond the top or bottom of the pusher grade, it will usually be found advisable, in spite of the added mileage, to have the pusher-engine service begin at the station. When the assistant engine is uncoupled from the train while running, the siding must evidently be at some little distance beyond the top of the grade, so as to give ample opportunity for the assistant engine to run onto a siding and have the switch turned before the train passes. All of these allowances add to the length of the pusher-engine service, which therefore makes it considerably more than the nominal length of the pusher-engine grade as taken from a profile of the road.
When we analyze the elements of cost, we will find that many of them are dependent only on time, while others are dependent upon mileage. Still others are dependent on both. Very much will depend on the constancy of the service, and this in turn depends on the train schedule and on a variety of local conditions which must be considered for each particular case. The effect of a pusher-engine on maintenance of way may be considered to be the same as the cost of an additional engine to handle a given traffic, as developed in § 198. The same total allowance for the expenses of maintenance of way (7.45%) will therefore be made. Although the cost of repairs and renewals of engines is evidently a function of the mileage, and would therefore be somewhat less for a pusher-engine which did little work than for an engine which was worked to the limit of its capacity, yet it is only safe to make the same allowance as for other engines. Other items of maintenance of equipment are evidently to be ignored. The item of wages of enginemen will evidently depend upon the system employed on the particular road. Whatever the precise system the general result is to pay the enginemen as much in wages as the average payment for regular service, and therefore the full allowance for Item 80 will be made. Similarly we must allow the full cost of the items for engine-supplies. While the engine is doing its heavy work in climbing up the grade, the consumption of fuel and water is certainly greater than the average; but, on the other hand, on the return trip, when the engine is running light, it probably runs for a considerable portion of the distance actually without steam, and therefore the consumption of fuel and water will nearly, if not quite, average the consumption for an engine running up and down grade along the whole line. That portion of fuel consumption which is due to radiation, blowing-off steam, and the many other causes previously enumerated, will be the same regardless of the work done. We therefore allow 100% for all of these items of engine-supplies. In general we must add 100% for Items 90, 91, and 94, the cost of switchmen and telegraphic service. While there might be cases where there would be no actual addition to the pay-rolls or the operating expenses on account of these items, we are not justified in general in neglecting to add the full quota for such service. Collecting these items we will have 45.05% of the average cost of a train-mile for the cost of each mile-run by the pusher-engine. Using the same figure as before, $1.50, for the cost of one train-mile, we have 67.57 c. for each mile-run.
Per cent affected.
Cost per engine mile, per cent.
Track material, labor, bridges ..
Steam locomotives .................
Road enginemen and engine-house expenses.............
Fuel and other engine supplies..
Signaling, flagmen, ana tele-graph....................