Working Conditions and Fuel Costs
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Fluctuations in Fuel Consumption Caused by Variations in Working Conditions Emphasize the Importance of Keeping Accurate Records
I AMalways careful, when'answering questions about the . figures in '"The Commercial Motor' Tables of Operating
Costs,'-' to point out that they are averages and can be bettered or worsened as a consequence of operating conditions. Average costs fit average conditions. if the conditions are difficult then the cost will rise. Other things May also have to be taken into consideration when making an estimate of what the cost of a job may be. One of the most important of these "Cost affecting conditions" was indieated in ari article describing a test of a Cornmer 25-cwt. van; by Mr: L. J. Cotton in the issue of The Commercial Motor-for Noveniber 6 last year.
With the .article he included a table which, so far as I , can remember, had never been used before in connection • with these test articles . I refer to the fuel-consumption table which is reproduced, as Table I with this article. The figures show that,. in the case of a vehicle running with full load the cost was 61 Per cent. higher when the vehicle was making a journey of four stops per mile as 'compared with straightforward running with no stops at all.
That is something which-any experienced driver will know; at least he will have a suspicion that it is to be expected but has probably never gone to the trouble of carrying out any tests himself.
Effect of Load The two sets of figures represent extremes, but are none the less useful and interesting. The table also shows how fuel consumption is affected by the load carried. All these things are taken care of when the Tables are compiled.
Most of the differences are covered by averages and it is the main reason why, in a table which relates to low weekly mileages the fuel consumption is seen to be higher than in those tables which give figures relating to vehicles covering weekly mileages which may be regarded as orthodox.
I particularly appreciated Mr. Cotton's figures when I received a recent letter 'containing many queries starting with the subject of fuel consumption.
It is because of these fluctuations in fuel consumption figures, as well as for other reasons which this article will disclose, that I repeatedly recommend operators to keep records from which they can arrive at their own costs. It is to be regretted that so few follow my advice.
The predominant item in running costs is, of course, fuel consumption. It is, fortunately, the one concerning which most users have some information and it is easy, therefore, to point the argument that I have just put forward by taking fuel consumption as an example. I have mentioned that frequent stopping and starting are ajcause of high consumption, and‘l quote Mr. Cotton's table ali an example., Other conditions which have a corresponding if not so prominent an effect include (a), the particular class of work on which the vehicle happens to be engaged; (b), the type of country which the vehicle has to traverse; (c), type of driver, and (d), the effectiveness and sufficiency of the maintenance.
Regarding (a) I have often referred to building construction as one which is hard on a motor vehicle. The materials which have to be moved are often difficult to handle and, therefore,difficult to load in such a way as to give the vehicle what might be called a " chance." Usually, new buildings, especially on housing estates, are erected in advance of the eonstRiction of the roads which will eventually lead to them. This means that the vehicle, in the course of the journeys to and from the site has to traverse exceedingly rough ground.
Even if there is a road in existence, the delivery of the materials 'often involves leaving that road so that the effect; so far as the vehicle is concerned is just the same as if there were no road at all. There is excessive wear of tyres, abnormal wear and tear of the chassis and, so far as fuel consumption is concerned that becomes particularly heavy. This is because, in addition to the rough going to which the vehicle is subjected, there is the extra fuel used in tow-gear running. In many cases, too, we have to reckon with the operation of tipping gears.
.Here is the opinion of a builder who, if he does not keep cost records quite as closely as I would like, at least does know what he is talking about when he discusses the use of motor vehicles on building work.
He tells me that the life of a popular make of light lorry is, in his experience, under two years. As the annual mileage in this class of work is almost invariably moderate, he has to write off his vehicles at thc rate of 50,000 miles Instead of at an average of 150,000 miles. He thus increases the single item of depreciation by 200 per cent. All the other items of cost are affected but not necessarily to the same extent.
It will readily be agreed that there are at least a dozen trades in which the conditions under which their transport is operated would be likely to affect the running costs of the vehicles. But it is not only the circumstances surrounding the kind of work involved that affect costs, but the way in which the vehicle is driven, how it is maintained, and in general the attention it receives at the hands of those responsible for its upkeep. Fuel consumption, tyre life, wear and tear of brake facings and the general condition of the transmission can be aggravated by 100 per cent. according to the magnitude and seriousness of the repairs necessitated by the neglect.
I will take two extreme cases. On the one hand, we have a vehicle employed on work which is favourable to good performance, in the charge of a careful driver, the vehicle being carefully and conscientiously maintained. On the other hand, we have one which is at work under difficult conditions, in the hands of a careless driver and neglected in so far as maintenance is concerned. It will be realized that an extremely wide variation in the running costs of the two vehicles is likely to be experienced.
I rarely consent to discuss the differences in cost of operation involved in light and loaded running. My reason is mainly one of policy, not technical. I am always reluctant to do anything to encourage rate cutting, by which I mean encouraging a man to think there are ways and means of reducing costs, whereas the chances of so doing are most remote. Putting this another way; it is not right to hold out hopes of economy in fuel consumption as a means for cutting haulage rates, when other considerations may affect that item of cost in such a way as not merely to eliminate the anticipated economy, but to cause increased rather than decreased expenditure.
As.a simple example of conditions of use which might easily upset any such calculation, I need only compare the fuel consumption of a vehicle constantly employed in congested traffic with another almost continually engaged on long non-stop runs on main highways. The rate of fuel consumption in the former case may be 50 per cent, greater than in the latter. Mr. Cotton's figures show that, in the case he examined, the increment was actually greater than that. Such an increase, as. the figures which I am about to disclose, demonstrate, more than offset any economy attained as the result of light rtuming.
Light Running I do, however, receive many inquiries in which the condition of light running is mentioned, this being an indication that the inquirer anticipates some economies may possibly be effected as the outcome of that condition.
I have endeavoured-endeavoured, I repeat-to find a figure for fuel consumption which will meet these circumstances. At the same time, I should warn all those to whom these figures have an appeal, that a careless driver, or some unusual traffic condition, such as, for example, one involving the negotiation of several miles of slow running in traffic, will upset all his calculations and render the.figures valueless. However, it may be as well to set down some figures for fuel consumption and how they are affected by the load.
I do not propose to go through the whole range of sizes and load capacities; but will confine myself to the most popular and widely used vehicles. Moreover, I propose to confine myself to the carriage of goods, not passengers. The conditions of passenger transport are rarely such as to make it possible to state, with any degree of accuracy, what proportion of load is being carried throughout a particular journey.
I must emphasize again that the figures given must be used with all reserve, but, given that qualification, readers may find the information useful in cases where quotations are requested in connection with long-period contracts, the contractor being well acquainted with the details.
Figures for Four Conditions Table II gives the figures under four headings. There are those which would apply in the case of vehicles which normally carry a full load, and others which, on the average, carry such a load for 75 per cent, of their running time, These are usual conditions and are those to which the figures in the Tables apply. The third series is, perhaps, the most interesting as giving figures which may be expected in connection with vehicles which are fully loaded one way and return empty. Finally, there are data relating to the fuel consumption figures and cost relating to vehicles which habitually run light.
It is of interest to note the differences in weekly -expenditure on petrol, for some extreme examples. First, a 3-tonner, the smallest of those concerning which this information is given. At 400 miles per week the expenditure on petrol, assuming that the vehicle is fully loaded all the time, is 16 13s. 4d. If the vehicle is fully loaded for only 75 per cent. of the time, as would be the case if it ran in one direction fully liaded and brought back full loads on only every alternate trip, the-full cost would be £5 18s. or a saving of 15s. 4d. per week.
On the basis of 50 per cent, loading, the fuel cost is £5 lls. Bd. and the saving El Is. Bd. This is •the most frequent condition in the operation of C-licensed vehicles.
In the case of a 15-ton lorry, also running 400 miles per week, on work which provides traffic sufficient tG keep the vehicle fully loaded for 100 per cent, of its time the consumption is at the rate of 41 miles per gallon, the cost working out at lid, per mile. For 400 miles the expenditure on petrol is thus £18 6s. 8d. If the vehicle is loaded so that its loading characteristic is 50 per cent„ the m.p.g. may average about 51 and the cost per week will, on that basis, be 400 times 9.10d., which is f15 3s. 4d. The difference is 13 3s. 4d. • S.T.R.