Do You Know the ling of Ton-miles?
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MY young haulier friend to whom, some time ago. I gave assistance in setting up a costing system, is in trouble again. He came to me the. other day and asked how •he was to get out a figure for the cost per tonmile of the traffic he was carrying.
" You are asking me a question which is far from easy to answer " I said.
f' But," he replied, " I have heard a lot of talk about the ton-mile ; everyone refers to it at some time or other in the course of conversation, and I thought it must be something which everyone understood."
"That is just the trouble,' I answered. "So many people use the term and so few really know what it means. An accurate figure for cost per ton-mile is, as a rule, so difficult to calculate, and involves such a tremendous amount of bookkeeping, that it is reasonable to say that it is impracticable to arrange for its computation. Indeed, my general rule when I am asked to deal with the problem is to suggest that it is something better left alone."
" I hope you won't say that to me," he replied, " because this is something the boss has' asked me to do and I can't very well 'tell him that he is asking the impossible."
" What do you understand by the expression?" I asked.
"To tell you the truth." he said, "I don't understand it at all; I don't even know what a ton-mile is. I have often wondered what it -might be, because I have a cutting from The Commercial Motor,' which I have kept for some time, referring to a type of vehicle of which we have several, a 15-ton Albion. It is a report of a road test, and there are some figures for ton-miles-per-gallon quoted in the summary which 'have always puzzled me."
"Have you got it handy?"
" Yes, I can soon find it," he said, and in half a minute he produced it. "This," be continued, " is the part that I have in mind," and he pointed out to the this sentence' Under easy conditions,' 240 gross-ton-m.p.g., 164 pay-load ton-m.p.g. ; under hard conditions, 177 gross-ton-m.p.g., 120 pay-load ton-m.p.g.'
"I suppose I ought to be ashamed to conles it," he said, "but I don't understand a single word of that."
" We will have to look up some of the other figures in the summary before I can explain it to you," I answered. " First of all, we want the figure for the groSs load, which is the total weight of the vehicle, the paasengers, driver: load, etc. I see that is 22 tons. Then we want the payload. That, I see, is 15 tons.. Now, for eVery mile that the
vehicle travels it does 22 gross-ton-miles and 15 pay-load ton-miles, so that, if it runs for 20 miles, the gross-tonmiles covered is 440, and the pay-load ton-miles 300."
" I see," 'nc replied. " You multiply the weight by the mileage."
" Exactly," I said. " Now, we want something else. We want to know the fuel consumption in miles per gallon. Will you look that up for me?"
"I see there is a paragraph headed fuel consumption." he answered. "It states that on an out-and-return 10mile route over undulating main roads the fuel consumption is equal to 10.92 m.p.g. ; on an 18.1-mile out-and-return route, including thick traffic and a first-gear hill, 8.05 m.p.g. Then comes the bit about ton-m.p.g." Good," I said. " Now, it seems fairly clear that what is meant by easy conditions is the first run of 10 miles over undulating main roads, when the fuel consumption was the equivalent of 10.92 m.p.g. I think we will deal with that before we go any farther. The point to note is that, in consuming a gallon of petrol, the vehicle ran 10.92 miles. As the gross load was 22 tons the ton-mileage was 22 multiplied by 10.92, which is, as near as makes no matter, 240. That is how the first figure of 240 gross-tonm.p.g. is calculated."
"And the others in the same way? " he butted in.
"Yes, and I suppose I may now take it that you understand how the figures for grossand pay-load ton-m.p.g. have been reached."
" Yes," T see that now, but why give separate figures for gross-ton-m.p.g. and pay-load ton-m.p.g.? Which is the one that concerns me? " he asked.
"The second one—the pay-load ton-m.p.g. The first one is more important to the manufacturer of the vehicle and the engineer or designer. It gives him an indication of the overall efficiency of his machine, of the capacity of the engine, of the ease of running .of the transmission and, snore particularly, the suitability of the gear ratios for the load carried, having in mind the size and pbwer of the engine. Irowever, we won't. go into .that, which is a technical -problem, 'but will-confine ourselves to-:the pay-load tors.rn.p.-gi which, although it is no answef to your question, has a good•deal to do with it."
This eXplanation-is 'good in one way," he said, " but
not so good in another, for it has raised a new problem." " What is that? " I asked.
" Well," he said, " there are, in this summary,. two figures for pay-load ton-m.p.g. One, under easy conditions, of 164-ton-ut.p.g., and the other, under hard conditions, of 120-ton-m.p.g. There is a good deal of difference there, and I am wondering which is the figure of inteest to me."
" They are both of interest to you," I replied. " for they indicate to you that, where the work which you are doing is over give-and-take main mods, you are likely to get 164 pay-load ton-m.p.g., but, if you are working in hilly country and traffic, you may get only 120-ton-mpg." " As a matter of fact," he said, " the bulk of the work that we do is long-distance haulage, and I suppose that means it goes under the category of easy conditions. At
• the same time there is, near the end of most journeys, a good deal of dense traffic to be negotiated—in London, Birmingham, Liverpool, Manchester and the like. Moreover. some of our traffic runs are between Leeds and Liver1)001. which means that we have some fairly stiff hill-climbing to do.. I suppose that means my figure for pay-load ton-m.p.g. will come-between those two extremes?" " That is a fair summing-up of the situation," I answered, "but, if you want such figures as a basis for your costing, you must get them from yonrl own records ' and not take anyone else's word for 'it."
" Yes," he said. " I quite appreciate that. It was one of the first things you drilled into me when you were explaining costing."
" Do you begin to see daylight? "-I questioned.
" All that I can say," he said, "is that I now understand .what is the meaning of the term ton-mile. These figures do not give me any indication of cost, for they refer only to fuel consumption."
"'It is not difficult," I said, " to give you a cost figure comparable with that. What mileage, per week, is your 15-tonner doing? "
"Between 500 and 600," he replied. " For that," I said, "we can take; on to-day's figures, 18d. per mile as a vehicle-operating cost. For every mile that the vehide runs, assuming that it is loaded to capacity, the ton-mileage is 15. Your cost per ton-mile is, therefore, 18d. divided by 15, which is 1.2d."
" I thought you said it was difficult," he protested. "There doesn't seem to be anything difficult in that." " You have overlooked something," I replied. " I was careful to say ' that the vehicle was loaded to capacity.' Are your vehicles always so loaded?"
"Not by any means," he said, ruefully.
" That is where your .problem begins," I said.' "Suppose on a particular journey the vehicle happens to be tarrying only 5 tons. The pay-load ton-mileage per mile run is then only five and your cost per pay-load ton-mile is. now 18d., perhaps a little less, because the fuel consurnp' tion may be less, but not enough to matter, so that the cost per pay-load ton-mile is now 18d. divided by five, which is "I see," he interjected. " What is the cost per pay-load ton-mile when the vehicle is running empty? " " It is infinity." I answered.
" What am I to do about it then? " he asked.
" Candidly;" I replied, "1 don't know. Suppose you give me the story of a week's work for one of these lorries, and we will use that as a basis for calculating the cost per ton-mile of the traffic carried."
"Here as one," he said, "a 15-tanner, lorry No. 37, for the week ended September 25 of last year. It set out at the beginning of the week from-Leeds and went to Bradford empty. It picked up a load of 15 tons and took it to Birmingham, where it dropped 10 tons and then ran on with the balance of 5, tons to Coventry. It picked up 12
tons in Coventry and ran to London, dropping 10 tons at one point and running a further 10 miles with a balance of 2 tons. It came back erfrpty over that 10 miles, picked up another 15 tons, which load it carried to ,Manchester. Of that total, 12 tons were dropped at Manchester and the remainder taken to Wigan. It weril from Wigan to Liverpool empty, picked up 8 tons in Liveripool for Halifax, and returned empty from Halifax to Leeds."
" A nice little run," 1 said. " Just about as complicated as it need be in order to show the difficulty of asses,sing costs per. ton-mile. I will deal with the journey, item by, item, to show how the ton-mileage varies. 1 won't bother about accurate mileages, but just take a round, easy-figure, so that our ton-mileage will he easy to calculate."
" Will it be all right to do that?" he asked. " Is it not necessary to be particularly accurate in this matter? "
" When you get right down to the job of assessing your actual figures, if ever you do get down to it," I said, "accuracy will be necessary but, for the time being, all that I want to explain to you is the principle involved.
1` Now, from Leeds to Bradford we can take to be 10 • miles, the vehicle running empty so that the ton-mileage was nil. From Bradford to Birmingham is 110 miles and, for that distance, 15 tons were carried all the way. The ton-mileage is 15 by 110: that is 1,650. Now, we have agreed that the cost per mile run is _Is. 6d. and for 110miles that is E8 5s., so the cost per ton-mile is 1.2d. That is the figure we have already obtained in discussing what the cost per ton-mile was when carrying a full load.
"Now 10 of those 15 tons were dropped in Birmingham, and the vehicle ran with the balance of 5 tons to Coventry_ The distance is.20 miles so that.the ton-mileage is 100. The cost, at 18d. per mile, is Ll 10s. and per ton-mile 3.6d.
" Perhaps it would be better," I added, "If We set these journeys down, mile by mile, giving the load carried, the mileage, the ton-mileage, the cost of the journey and the cost per ton-mile." This we did, with the result as set out in tabular form herewith.
"Now,' I continued, "you see ivhat I meant when 1 said that the assessment of cost per ton-mile, if it is to be done soas you get a cost per ton-mile for every lot of traffic you carry, is going to be enormougy difficult."
" Yes," he said, "I don't like to have to do that for every journey that each of our vehicles does."
" No, I thought you wouldn't," I replied. "We can, from this table, get an average figure for the cost per pay load ton-mile for that vehicle during that week. The vehicle has run 560 miles and has done 6,200 ton-miles, that is pay-load of course. The cost of 560 miles is 18d, per mile, a total cost of £42, so that the average cost per pay-load ton-mile is 1.63d."
" It is not so difficult after all," he said. •
" Wen, I don't know," I answered. ". You still have to reckon up the ton-mileage, bit by bit, of every, journey for, without doing that, there is no way of obtaining the figure of 6,200 for the total ton-mileage. sx.R.