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Longer Leads Need Larger Lorries

3rd February 1950
Page 52
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Page 52, 3rd February 1950 — Longer Leads Need Larger Lorries
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Which of the following most accurately describes the problem?

1 N the prelimin.try investigation in examining the relative economic merits of three sizes of vehicle, a 6-tonner (30, m.p.h.), a 7.and a 14-tonner. all oil-engined, I assumed standard loading and unloading times-10 mins. per ton per load plus 10 mins. I added half an hour at each end of the journey for unexpected delays.

As a preliminary to the discussion I tabulated figures for current operating costs of the three types and arrived at the following figures:.

For the 6-tonner 7s. 3d. per hour and 4d. per mile..

For the 7.1,-1onner 8s. pet hour and 5d. per mile,

For the I4-tonner Ils. per hour and 71d. per mile.

These figures are operating costs only,with no provision for profit.

So far I have dealt with lead distances of 10 miles and 90 miles, Now let us take a lead of 180 miles. Taking the six-tormer, 7 hrs. will be necessary for travelling the outward distance, so that it will be but a little short of '11 hrs. by the time the vehicle has been loaded, travelled the 180 miles, and unloaded. The next day the vehicle will get back to its starting point in a further 7 hrs. travelling. 1 think it will be sufficiently accurate to base our calculations on that one complete journey. The total time is 18 hrs., I 1 on the first day, seven on the second, and the cost of that at 7s. 3d. per hour is £6 10s. 6d. The vehicle has travelled 360 miles at a cost of 4d. per mile, which is £6. In addition. I must take into consideration 12s. for a night's subsistence and expenses. The sum of these three is £13 2s. 6d.. which is equivalent to a cost of £2 3s. 9d. per ton.

In the case of the 71-tonner. practically 10 hrs. will be needed for travelling time so that on the first day, if we reckon 2 hrs. for loading and 9 hrs. travelling, the driver will be • 162 miles on his way when that day is finished, and he must 'put up for the night. Next Morning, in 1 hr., he finishes the journey by travelling the remaining 18 miles and takes another 2 hrs. for unloading at his destination. That leaves 8 hrs. 'of that day to set out on the return journey, and in that time he should cover 144 miles, : leaving 36 miles on the third day, which should take another , 2 hrs. That rouw journey has thus taken 24 hrs. and 'the cost is £9 12s. for time, plus £7 10s. for mileage. plus £1 4s. for subsistence and expenses; a total of £18 6s., and that cfividecl by 7,1 gives us about £2 10s: per ton.

The time needed for the 14-tonner can quickly be calculated by reference to that for the T.',-tonner, if it be realized that the difference between the two is the loading and unloading time only. On that basis the time is 26 hrs.. which. at I Is. per hour, is £.14 6s: The mileage is 360 at 71d. per mile, which is £11 5s., plus £1 4s. for subsistence and expenses. so that the total is £26 .15s. for the 14-tonner. The cost per ton is, .therefare. £.1 18s. To summarize these results, it seems clear that for the

TABLE IV Cost per ton for vehicles of various capacities over varying leads.

Legal limit for all vehicles-30 m.p.h.

(10 min. per ton plus 40 min. loading and unloading.) Lead (miles) 6 tons , C s. d.

10 ., 664 90 1 3 31 180 .. 2 3 9

increases, the heaviest vehicle comes more and more into its own until at 180 miles it is easily the cheapest. The Thtonner, judged by economic considerations alone, does not compare with the other two.

The results of the calculations in this and the previous article are set out in Table II, in which it is made, I think, perfectly clear that the 7.1e-tormer is the most expensive machine, the cost per ton being higher with that vehicle in all cases except as regards the 10-mile lead, for which, as might be expected. the heaviest vehicle shows to disadvantage. The reason why this should be so I have already suggested. It is that the standing time is great in proportion to the running time, and standing time in the case of maxim LI in-sized vehicles is particularly expensive.

In order to make the matter more clear I have in Fig. 1 set out the results of Table II in graphic form. The cost per ton with the 14-tonne!. is highest until the 22-mile lead is reached, when it crosses the curve of the 71-tonner. which thereafter is the most expensive. The 6-tonner is the cheapest until the 42-mile :lead is reached. Here the curve of the 14-tonner crosses it and becomes from then on the lowest in cost per ton carried.

In view of what I have stated about the importance in this matter of standing time, it will be interesting to take a different set of conditions in which that time is less than what was taken in the earlier set of examples. Suppose it be imagined that, as the result of more efficient organization at terminals, the loading time for any size of vehicle is reduced to 3 mins. Per ton plus 10 mins., and that other occasional delays which were provided for at the rate of half an hour at cach end of the journey are reduced to a quarter of an hour.

In the case of the 6-tonner. the time for loading will be 3 mins. times six, 18 mins., plus 10 mins.. making 28 mins., plus 4-hr. allowance for occasional delays, 43 mins. in all. The time taken for unloading is assumed to be the same, so that the total terminal time will be 1 hr. 26 mins. The time for the journey is not affected. and a I0-mile lead is assumed to take one hour. The total time per round trip is thus 2 hrs. 26 nuns., which, at 7s. 3d. per hour. is 17s. 8c1., to which must be added the cost of 20 miles at 4deper mile, 6s. 8d.. giving a total of :El 4s. 4d. per journey, which is 4s..'0.;c1. per ton.

For the 71-tonner, the terminal time similarly calculated

is 'mins. .at each end,.imaking 1 hr. 35..ntins„,altogether.

It takes 11 hrs to travel the 20 miles, giving us 3 hrs. 5 mins. for. the round trip. The cost of that at 18s. -per hour is JO 4s, 8d. Add 20 miles at 5`d., 8s. 4d., and the total cost becomes El 1.3s.. or 4s. 4.4f, per ton.

A terminal time for the 14-tonrier is 2.i hrs, and the travelling lime I hr. 40 mins., giving 4. hrs. 5 mins.. which, at I Is. per hour, is E2 4s. i Id. Add 20 miles at 7.1d. per mile, 12s. Cod., and we get a total cost of E2 17s. 5d., which is 4s. 1,41. per ton. Already the 14-tonner is showing to greater advantage thw-I it did in the first example.

Taking now the 90-mile lead. the terminal delays will be the same as in the exiimple just quoted and the travelling time will be equal to those which were given when it was assumed that the terminal periods were longer.

In the case of the 6-tonner, therefore, we have the terminal time of 86 mins. and a travelling time of 7 hrs., giving a total of 8 hrs. 26 mins., for which, at 7s. 3d, per hour, the cost is 13 Is. 2d, Add for 180 miles at 4d., E3. total•E6 Is. 2c1., which is El Os. 3d per ton. In a similar manner. it can be shown that for the 7i-tonner the cost is El 3s. VIA., and for the 14-tonner 18s. 101d.

Over the 180-mile lead, still With this short 'period of terminal time, the cost can be shown to be, for the 6-tormer £2 Os. 7d. per ton,for the 7,1-tonner £2 5s. 4d. per ton, and for the 14-tonner El 10s. 3d. per ton. These otriclusions are indicated in Table HI.

It will be useful as well as interesting to go through a similar set of estimates, this time assuming that the speed. lirnit for vehicles weighing more than 3 tons is increased from 20 m.p.h. to 30 m.p.h.

Before proceeding with the figures which will apply to those conditions, I. should. like to remark on the subject of those suggested increases in speed limit for heavier vehicles and the delay in bringing .them into force. That delay is something which 1 earthot. understand I have read time

and again the arguments for and against, and I understand that at the moment the only opposition lies with the trade unionists. That, to My mind, is the most incomprehensible aspect of the whole affair. everyone who travels the roads in this country, and I do a little myself, is fully aware that Most drivers of heavy vehicles break the law relating to speed limits on every journey they make. There may be exceptions to this, but I have yet to meet one. Day after day, those who drive cars are continually overtaking 20-m.p.h. vehicles which are running upwards of 30 m.p.h.

It is, of course, unnecessary to deal with the six-tonner in these calculations as that vehicle, in what has gone before, has been taken as adhering to the limit of 30 m.p.h

I 'Will. I1lt first lhti terminal conditions which' applied in the or 511 set of estimats, namely, that the time to load is 10 mins, per ton plus 10 mins. and the same time is required to unload In aduition. there is 30 mins dela,: at each end.

For the 7},-tonner. therefore, the terminal delay at each end is 75 mins. phis 10 mins plus '30 mins., which is 115 mins., and the total for loading and unloading is. therefore, 3 hr,, 50 mins. The travelling time is now the same as for the six-ionner and that over a 10-mile lead has been taken as one hour out and home. The total time for the complete thp is therefore 4 hrs. 50 mins.. and applying the same methods as before it can be demonstrated that the cost per ton is 6s. 3.W.

In the ca',..; of the 14-tanner the terminal delay, as estimated corlier in this article, is 6 hrs. altogether With an how travelling, that makes 7 hrk for the complete journey and the cost assessed on that basis is 7s. 31d per ton; still, it should be noted, in excess of either of the other

two In this case. however, it may be necessary to assume that the full eight-hour day is allocated in respect of this one journey. That will bring the cost up to 8s. per ton. With a 90-mile lead. the costs are similarly shown to he fi Is. 8d. ins the 71-Partner, which is just able to complete the round journey in an 11-houi day,.

For the 14-tonner, 13 hrs. are, required' and this means that that allowance must be :made for subsistehce and expenses for one night in relation to each round trip. Hven so, the cost per ton is only 18s. ltd.

The figures for those calculations are set out in Table 1.V. which demonstrates that except for the shortest lead. the 144onner is now the least expensive vehicle to operate, which is what might have been expected,

It is of interest to note that the cost per top as the result of the increase in 'the speed limit has been. reduced by nearly 6s To complete the story., I have gone through the same Let of calculations assuming the shorter terminal delays as before and the figures for this are set. out in Table V. Now the 14-tonner is, but for the d. per tbn which might be easily eliminated, the cheapest vehicle over all distances of 10. miles upwards.

hi Figure 2, I have draws a graph which is based on the figures in Table IV. This.heeds, I imagine, no further explanation. It shows. that evenWith a longer terminal delay of 6 hrs. per .week, the 14-toriner is the more economical vehicle for leads Of upwards sf 40 miles.

S T.R.


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