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The Ton-mile Factor can be Misleading

6th July 1951, Page 52
6th July 1951
Page 52
Page 55
Page 52, 6th July 1951 — The Ton-mile Factor can be Misleading
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Which of the following most accurately describes the problem?


ANY of the.inquiries T get about the ton-mile come from transport managers of companies operating fleets of vehicles under C licences. Usually the director of a manufacturing concern makes some inquiries into the efficiency with which his fleet of vehicles is being operated. He does not know much about the subject, least of all about the intricaeies of costing road transport, but , he has heard somewhere the term "ton-mile." It is familiar in connection wish rail transport and, therefore, if he looks over the transport manager's figures for cost and finds that there is nothing entered therein from which he can deduce the cost per ton-mile, he promptly asks why.

The transpoit manager probably knows how impracticable it is to quote an accurate figure for the cost per ton-mile but. of course, agrees to. provide some figures at a subsequent date.

The first thing to do in tackling this problem is to make sure that we know exactly what is meant by the term " ton-mile." Actually it is weight multiplied by distance, weight in tons multiplied by the mileage that that number of tons is carried. It can perhaps be best explained by example. If the reader will turn to the issue of "The Commercial Motor" for March. 9, he will find a report on the road test of the Bedford 7-tonner. There is a paragraph in that -road test which runs: "Fuel consumption; 9.3 m.p.g. at .29.4.. ni.p.h. average speed, that is, 97,2 gross ton-m.ptg. or61.9 payload ton-mpg. as tested."

. . . ,

Cross and . Payload Weights . .

As a. preliminary, to explaining what is meant by gross Ion-mpg. and payload ton4n.p.g., it is first of all necessary to refer to the first paragraph in the test where the gross load carried 'by the .vehicle10 tons 8 cwt. 2 qrs. is given, and the payload-7 lord 6 cikt.

Now, for the expenditure of one gallos of fuel, 10 tons 8 cwt. 2 qrs., that is approximately 10.4 tons, can be moved over a distance of 9.3 miles. If that gross weight of 10.4 tons he multiplied by the.distance, 9.3' miles, the result is 97.2.. That is what is Meant by showing that the fuel consumption is equivalent ;497.2 gross ton-m.p.g.

The-payload, 7.3 tons; has been-moved the same distance for the expenditure of one gallon, and.jf_7,3 be multiplied by 9.3 the figure of 67.9-payload .tOn:m.p.g. results : The point to' note is that the ton-mile -iS.obtairred by multiplying the load by the miles run.

The point which perhaps needs a little explanation is the difference between gross ton-miles and payload tonmiles. The figure for gross ton-mileage per gallon is a matter of interest from the technical point of view. It indicates the amount of work measured in ton-miles Nihich

A38 this particular design of vehicle can do for the expenditure of one gallon of petrol. The figure is useful for purposes of .comparison between one make of vehicle and another.

It is the customer, the user of the vehicle, who is more directly concerned with payload ton-miles per gallon. He wants to know how much he can get in the way of ton-miles of actual useful load for the expenditure of his gallon of petrol.

Whilst the user is, of course, concerned with the number of payload ton-miles per gallon of fuel, he is, in thesense in which we are considering the subject in this article,, more directly concerned with the number of payload ton-miles he gets for is., or, to put it another way, he is anxious to know what is the actual cost to him per ton-mile of payload. He wants to know how much it costs to carry one ton Of payload one Mile.

If operators' vehicles were always fully loaded, the method of calculating ton-mileage either per gallon or per shilling would be exactly the same as that already discussed and set down in the figures relating to this road test of the Bedford 7-tonher. Unfortunately, that is seldom the case. The loads carried by vehicles fluctuate from full load to nil. They may be. part loads, the vehicle may carry a tew parcels or, sometimes, it may carry an overload. Just how difficult it is to calculate costs per payload ton-mile accurately can best be appreciated by the set of figures in Table I. These relate to a round journey made by a 7-8-ton lorry, the operating cost of which has been shown to be Is. per mile. It is assumed that the owner wants the cost per ton-mile for the loads this vehicle is carrying.

Let me run through the schedule item by item and show how the figures apply. The vehicle first leaves the garage and runs empty for 5 miles to the London depot. As no load is carried, the ton-mileage is nil and the cost of running this 5 miles is 5s.; the cost per ton-mile is 5s, divided by the load carried, that is to say divided by nil. The answer to that sum is infinity, in other words the cost per ton-mile cannot be calculated.

At the London depot the vehicle is fully loaded with 8 tons of material and runs 128 miles to Nottingham, the first stop. The ton-mileage is ascertained by multiplying 8 tons by 128 mites, giving 1,024. The cost of the journey is I28s., that is 128 miles at Is. per mile, and the cost per ton-mile is 128s. divided by 1,024, which is 1.5d.

Some 11 tons of the material are dropped at Nottingham. thus reducing the payload for the next trip of 26 miles to Leicester to 61 tons. The ton-mileage is ascertained by multiplying 611005 by 26 miles, that is 1751 ton-miles. The cost of travelling at Is. per mile is 26s., and the cost per ton-mile, obtained by dividing 175. ton-miles into 26s., 1.8d.

Fluctuating Costs There is no point in dealing item by item with all the various drops and pick-ups on this round journey of 968 miles, but 1 would like to draw the readers' attention to the way in which the cost per ton-mile fluctuates from point to point as the vehicle proceeds on its journey. Ignoring the short stretches during which the vehicle carries no load, the cost per ton-mile is at a minimum when the vehicle is fully loaded and it is then 1,5d.

As the load diminishes, the cost increases, and for the run from Newcastle to Edinburgh, 105 miles with only 1? tons on board, the cost per ton-mile is 8.5d. Similarly, on the return journey the cost per ton-mile falls again to 1.5d. as the vehicle runs fully loaded from Glasgow to Liverpool, but rises to Is. per ton-mile on the last part of the journey from Birmingham to London, when the load carried is only one ton.

The Table indicates the difficulty of obtaining real tonmileage figures, that difficulty in my opinion is so great as to make it not worth while to go to the trouble. On the other hand, the transport manager has been instructed to get out the figures per ton-mile, and the question arises; could some sort of figure be obtained which will be of any use and will serve the purpose of comparison?

Usually, the method is that which is indicated by the line at the bottom of Table I. Take the total.cost £48 8s. for the week and divide by the ton-mileage, 4,5891, giving 2.53d. per mile, which in a sense can be said to be the average cost per ton-mile for that week, and my general rule in advising transport managers on this point is to suggest that that is the only method which is practicable.

It has its difficulties, as I can show by taking one or two examples. Take the cost of a fleet which is engaged on the conveyance of machinery. Sometimes the vehicles are fully loaded, but quite frequently because of the need to make deliveries to fulfil urgent requirements, quite small loads are carried on the 5-6-ton lorries. Assume that the cost per mile of running the vehicle is 9d. During one particular week a vehicle is on comparatively short runs and carries 6-ton loads twice per day along a 20-mile lead and does that five days of the week. Each journey provides for the carriage of 6 tons for 20 miles, so the ton-mile per journey is 120. There are 10 such journeys in the week so that the ton-mileage per week is 1,200.

The mileage per trip is 40, that is, 20 miles out fully loaded and 20 miles returning empty, and there are 10 journeys, so that the weekly mileage is 400. The cost of running 400 miles at 9d. per mile is 3,600d., and if I divide that by 1,200 ton-miles I get a figure of 3d, per ton-mile.

The same vehicle another week is busy with emergency orders in the area, and conveys three I-ton loads, two Of these journeys over a 100-mile lead and one over a 50-mile lead. The ton-mileage is 200 for the long-distance run and 50

for the third journey. The total is 250 ton-miles. The actual mileage run is 500 and the cost of those journeys at 9d. per mile is 4,500d, The cost per ton-mile is 4,500 divided by 250, which is 18d.

Such figures as these for cost per ton-mile appearing in the last column of a long string of figures, will take a Iot of explaining if the transport manager is to prove to his owner that the efficiency of operation during the week when the ton-mileage cost was 3d. is no better than in the other week when the cost Per ton-mile is 184.,Which is one of Elie reasons why 1 am averse to uSing too-Miles 'in-calculations of this kind.

1 would like to hark back for a Morisent to that average figure of 2.534. per ton-mile which appears at the bottom of Table 1 to check its suitability for use in any practical way in connection with costs and charges. As an exainple, la me assume a straightforward run from London to Leeds and see if it will be possible to use that figure of 2.53d. as the basis of rates assessment.

The distance is 200 miles, so that for every ton carried to Leeds we should have to take the figure of 2.53d. as ;he cost per ton-mile and multiply it by 200, which would give 5064., or 42s. 2d. per ton. That, however, is assumed to he the cost only, and before we can go into any calculation of rates we most make some provision for establishment. costs and profits.

'The cost of operation of the vehicle is given at the top of the table as Is. per mile. Establishment charges will probably mean an addition of 44. per mile to that. That would increase the total of £48 8s. from Table Ito £64 10s.t. the cost per ton-mile including establishment costs would thus become 3.364. The total cost calculated per ton for the Leeds trip would then he 200 times 3.364., which is £2 16s. per ton, and that is probably a fair assessment of Ihk: total cost.

The trouble is that whilst in this case the llamas appe.irs to be reasonably accurate it is not, as I have shown in the second example, always safe to rely upon it. To give another example in the use of a 15-tonner, which we will assume costs Is. 64. per mile to run. This vehicle makes regular journeys from Leeds to London and back, making two trips in one week. During a typical week it will leave for London on Monday morning with 15 tons; it will unload in London and pick up 12 tons, bringing it back to Leeds by Wednesday afternoon. On Thursday morning it will take 14 tons from Leeds to London and return with a 15-ton load, finishing the' week by Saturday noon.

Loads and Leads

The ton-mileage in that ease on the outward journey on the Monday is 15 times 200, which is 3,000 ton-miles; carry back 12 tons, 2.400 miles; going out again on Thursday with

• 14 tons, 2,800 ton-miles; and carrying back 15 tons, another 3,000 ton-miles, That makes 11,200 ton-miles in all. The cost of running at Is. 64. per mile is £60 or 14,4004. Divide that by 11,200 ton-miles and the cost per ton-mile is nearly 1.34.

That is the cost of a vehicle which is well loaded in both directions and that is one of the.reasons why the figure of 1.3d. per ton-mile is so muels lower than 2.534. for the 8-tanner, although part of the economy is because of the fact that the I5-tonner automatically costs less per ton-mile than the 8-tonner.

What the difference between the two should be can easily be calculated. For the 8-tonner fully loaded costing Is. per mile, the cost per ton-mile should be 1.5d. For the 15tonner costing Is. 64. per mile, the cost per ton-mile is 15 divided into 18d., which is 1.24.

The point in putting forward the case of this'15-ionner is that it emphasizes the fact that in a fleet of different-sized vehicles, the ton-mileage figure will be even less useful for purposes or comparison than it is in a fleet where the vehicles are of the same size.

In conclusion, let me say that, as a rough check, applicable only in the case of a fleet of vehicles which is doing approxi-mately the same kind of work week in and week out, it is permissible to take the total tonnage carried and the total mileage run and multiply the two. That gives the total ton-mileage per week on an admittedly erroneous basis, and if that be divided into the total cost of the vehicles per week, a figure of cost per ton-mile can be ascertained for the

purpose required. S T.R.

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