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Which is the Best Vehicle?,

27th January 1950
Page 56
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Page 56, 27th January 1950 — Which is the Best Vehicle?,
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Which of the following most accurately describes the problem?

SELECTION of the most economical size of vehicle for any particular traffic can he most difficult. The factor of legitimate speed is one which must be considered, but it is not the most important. Lead distances, in relation to load capacity, are bf consequence and terminal delays, including waiting time as well as that properly required for loading and unloading. arc. particularly outstanding in this respect, • If it were possible to reduce the problem to the simple terms of an algebraic formula, then' speed, distance and standing time would be the three constituents of that formula.

The problem, incidentally, is of wide interest, for it is on Which the ancillary'user must have to solve as • frequently as the haulier. In acknowledgement of that fact, I 'propose, in the first place, to concern myself only with Costs and to omit referepees to rates and charges. .

Acceptance of the factor of terminal delays as being important in connection with the

choice of a vehicle makes it clear that almost every .case must, be decided on its merits, for the proportion of running and standing time vines with distance as well as with the .character. of the load, and -both'. Of these differ according to the class Of work. .! should point out that I 'am, in this discussion, leaving out any cOnsideration ofs, cases in which :there is a minimum-1 weight' of load if for example, the :Minimum Loa,/ be 10 tons, the question as to whether asix-toniter may he used clearly does not arise.

Choice Lies with the Operator

The class of work which must be considered. therefore. is that in which a given tonnage is available for conveyance daily, leaving the choice of vehicle to the operator, thus allowing him to decide whether he will use a small machine and make a larger number of journeys per day or a bigger lorry making fewer journeys.

A simple and straightforward case which will serve to demonstrate the principal aspects of the problem is one in which. flour in bags' is to be conveyed. • The operator, assuming that there is sufficient hat& to justify the use of the maximum-load eight-wheeler, and provided that other factors turn out to be in favour of such a vehicle, will in the first place have to consider the relative merits of a (s-tonner. a 70On maximum-load four-wheeler and a 14-ton maximum-load eight-wheeler. lie will. I think, decide that whatever size of vehicle he will choose. the power unit will be an oil engine.

As a preliminary. I have worked out some figures for the operating cost of these three types of vehicle. That informatkin is set out in Table I. The first point which arises is the period of depreciation which has been taken, For the 6-tonner I have assumed five years, for the 71-tonner seven years and for the 14-tonner eight years.

1 have included depreciation in the fixed costs rather than. as usual, in the running costs, because otherwise the calculations would he particularly complicated owing to the nee. ity of varying the amount debited against depreciation ,iecording to the annual mileage, which. in a problem such as !his, can vary.

For fuel cost I have taken Is. 9d. per gallon, that being d. more than the bulk price. In assessing the cost of tyres 1 have taken into consideration the-latest increases in price of 10 per cent: for covers and 5 per cent. for tubes. It may be noticed by those who have copies of "The Commercial Motor" Tables of Operating Costs that the amount quoted for maintenance is somewhat higher in this Table I than it is in the Tables. My investigations of late have shown me that in order to comply with ',relent conditions there is a .need for that increase.

, In what follows I am taking -sround figures for the cost per hour and the cost per mile: for the 6-tOntier ,7s. 3d. per hour and 4I. per mile:for the V-tornier 8s. per hour and 5d. per mile; and for the 14-toiiner Its, per hour and 714.1. 'per mile. in dealing with the problem I propose to take as a .basis for calculating loading and unloading times 10 minutes per. ton plus 10 minutes. In the _case at the 6-tohner, loading time wid be six times 10, plus 10, giving me I hr. 10 mins. As the unloading time is assumed to be thesame as the loading time, that gives me a minimuni terminal period of 2 hrs. 20 mins. I am going ftirther in this, inasmuch, as I am assuming that, as is so often the case, there are additional delays which amount to one hour per journey with each vehicle. That gives me a total of 3 hrs. 20 mins. for the 6-tonner.

In the .case of the V.,-tonner the net loading time. is 74times 10, plus 10, which is I hr. 25 mins, for loading plus the same for unloading, plu's 1 hi waiting time, giving a total of 3 hrs. 50 mitts. A similar calculation for the 14-tonner gives me a total terminal period of 6 hes. per journey:

Disadvantage tor Big Vehicle .

The cost of terminal periods for each size of vehicle is as follows: for the 6-tormer, 3 hrs. 20 mins. at 7s. 3d. per hour, £1 4s. 2d.; for the V.-tonner, 3 hrs. 50 Mins. at 8s. per hour, £1 10s.; and for the 14-tonner. 6 hrs. at Its per hour, £3 6s. That is equivalent to approximately 45. per tun"ettch for the two smaller vehicles and 5s, 6d. per ton for the largest machine, which therefore starts at a disadvantage.

Having dealt with the question of cost of terminal periods,. it is now passible to consider the effect. of Varying .lead distances. I will take a 10-mile lead as my first example. A reasonable time far a 6-tonner to cover 10 miles,. including a probable slow start out of an intricate passage leading to the mill yard, is half an hour. one hour for the total journey. Add the terthinal time, 3 hrs.' 20 mins., and we get a total-travelling" time of 4 hrs. 20 min. It should,.therefore, be reasonable In expect the vehicle to do two journeys per day in nine hours. The cost can he assessed as 'being nine hours at 7s. 3d. per hoot'. which -is 13 55. 3d, plus 40 mites at 4d. per mile, 13s. 4d-. Total cost for the

two journeys is then £3 18s, 7d., for which 12 tons have been delivered. The cost per ton is thus 6s. 61d.

Now for the 71-tonner. Whereas the 6-tonner is permitted to travel at 30 m.p.h, and I have taken an average of 20 m.p.h. over the short lead, the 71-tonner may travel at no more than 20 m.p.h., in which case we may take three-quarters of an hour as the time needed to cover the one-way journey and 11 hrs. for the round journey.

The terminal period, as assessed above, is 3 hrs. 50 mins., so that the total time for the journey, including loading. unloading, travelling and returning, is 5 hrs. 20 mins., which means that the operator would probably arrange for the vehicle to do two journeys in 11 his. The cost is 11 hrs. at 8s., £4 8s., plus 40 miles at 5d. per mile, 16s. 8d., giving a total of £5 4s. 8d. for the conveyance of 15 tons. The cot is thus approximately 7s. per ton.

One Run Per Day

• Now to deal with the 14-tonner. It needs six hours at the terminals and can be taken as requiring 50 mins. each way for the trip: The total time is therefore 7 tars. 40 mins. per journey, which means that in practice the vehicle will. do one journey per eight-hour day. The cost is for eight. hours at Ils. per hour, £4 8s., plus 40 miles at 71d., El 5s.. the total being ES 13s for the 14 tons which have been . carried. The cost per ton is thus slightly over 8s, . According to these calculations, viewing the matter solely from the economic angle, the vehicle to be preferred is the smallest of the three, the 6-tonner. • Now let us increase the lead distance to 90 miles. The 6-tonner, a 30-m.p.h. machine, should do the 90 miles in 31 hrs., that is 7 hrs, for the total journey. Add 3 hrs. 20 mins. for terminals and we get a total of 10 hrs. 20 mins., say, one load completed in an 11-hour day. The cost will he 11 times 7s.'3d., which is £3 19s. 9d., plus 180 miles at 4d. per mile, £3, total /6 19s. 9d1, which is equivalent to 11 3s. 31d. per ton.

The calculation for the 71-tonner is more complicated. Its speed limit is 20 m.p.h. and it will take at least five hours to run the 90 miles. If therefore the driver loads in a morning, travels the 90 miles and unloads at the other end of the journey, his time will be five hours for travelling plus 3 hrs. 50 mins. for loading and unloading and terminal delays, making 8 hrs. 50 mins., say, nine hours.

For this calculation to apply 1 have to assume that it is practicatle to unload at the destination when he arnives and that the reception desk is not closed for the day when he reaches there. Making that assumption it is obvious that the driver and the vehicle will have to stay the night at the outward end of the journey.

On the second day the driver will make thereturn journey, taking five hours, will load, taking 1 hr. 55 mins., and set out on his way with the second load. If he travels 36 miles and takes 2 hrs. 5 mins. to do that then he will have completed his second day of nine hours on the job.

On the third day he finishes the run

and takes 31 hrs. to do the 64 miles that are left. He takes 1 hr. 55 mins., say, two hours, to unload, and returns home in a further 5 hrs. making 101 hrs, in all. The total time taken is 281 bra., in which time he has delivered two loads of 71 tons each and has run 360 miles, The cast is 281 hrs. at 8s., which is £11 8s., plus 360 miles at 5d., which is £7 IN. The total cost is therefore £18 18s. To that it is necessary to add another £1 2s. to cover the driver's expenses and subsistence for the two nights, so that the total outlay is £20, which is equivalent to £1 6s. 8d. per ton.

Now to turn to the 14-tonner. Over a fairly long distance, such as 90 miles, • it is reasonable to assume that this vehicle will keep up the same average speed as the 71-tonner.and will therefore cover the distance in five hours. The loading and unloading time has been given as six hours, so that assuming that the vehicle works 11 hours, the work done will be similar to that of a 71-tonner. The driver will load, travel, the outward journey and unloadin that time. Driver and vehicle will stay the night at the outward end of the journey.

On the second day the driver will commence to return and iii five hours will be back at his loading point. He will take three hours to load and in the, remaining three hours of the ,11 hours will travel 54 miles on his second outward journey. .

On. the third day, the remaining 36 miles should be com

pleted in two hours. The driver will unload in three hours and return to his Starting point in a further fivehours. It will be safest to assume that for this total trip three full days of 11 hours are occupied. The cost will therefore be .33 hrs. at lls. per hour, £18 3s., plus 360 miles at 70., 111 5s.; giving a total of. £29 8s. Add to that £1. 2s., as before, for the expenses and subsistence allowance, and the total-cost of the trip is seen to be 130 10s. For that expenditure, 2.8 tons have been carried at 1 Is. 9d. per ton. • It shonld be noted that the assumption has been made that in none of these three cases is a loader required, it being taken for granted that there will he help available at each end of the journey.

Savings Offset Costs

, Another point which may be brought up in criticism Is

• none of these calculations have f .made provision, for the extra cost of overtime to be Paid to the driver in respect of the hours worked over eight or 81 per day, as the case may be. I have not overlooked that extra cost, but have followed the rule which I have found reasonably applicable in such cases, namely, to assume that the saving in respect of the other items of fixed costs, including overheads, because of -the fact that the vehicle concerned works for many more hours than 44 per week is sufficient to offset the extra payment for overtime. Calculations which I have made, and have from time to time set down in these articles, have generally shown that there is not much in it either way and that my assumption is normally justified.. I should regard it fair to make an exception to that rule in cases where Sunday work is involved as that necessitates the payment of double time, which would

eXceect the savings in fixed costs. . ' •

In mY next week's article.I shall pursue this subject more fully, taking instances of.langer leads. As the subject of the proposed increase in the' speed limit for vehicles over three tons unladen weight is pertinent to-day. I .shall also deal with this -and. show the economies which could he effected by such a change in the law. Even without such an. amendment, I shall' prove that the E4-tonner is the most economical vehicle over longer leads, and the 6-tonner over

shorter distances. S.T.R.


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