THE SIZE OF THE TRAFFIC UNIT.
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Why Neither the Bigger nor the Smaller Unit is Necessarily the Better for Every Purpose.
IN THE RECENT discussion on the relative merits of railway and motor transport, there has often been noticeable too much disregard of the influence which the size of the traffic unit has upon the cost of transport and the adequacy of the service provided.
From the point of view of economy in operation, _ either of road or railed transport, the advantage is all with the largest possible unit, provided that the business is sufficient to keep that unit fairly fully occupied. Even if we consider only the different types of commercial motor vehicle, we know that it is a .fact that the lowest costs per ton mile can be • obtained with vehicles of the highest load-carrying capacities. No one expects a 1-ton van to be operated at one-fifth of the cost per mile that would be reasonable for a 5-ton lorry. Nevertheless, a one-tonner and even smaller vehicles are frequently used partly because they are more speedy, and partly because the 'sub-division of loads leads to more prompt retail delivery over a wide area.
The small unit is, in fact, employed when time is of the essence of a contract. On the other hand, when time is of little or no value, the big unit.is preferred for any work sufficient to keep it regularly and fully occupied. Viewing the problem from a national standpoint, we have certain big haulage jobs of a regular character involving the transport of fairly constant quantities of heavy or bulky materials, regular supplies of which must be maintained everywhere. Under normal conditions, the right plan is evidently to maintain adequate stocks at an adequate number of points and continually to replenish those stocks by the employment of the cheapest possible form of transport. If stocks are not maintained, and we live from band to month, we may be compelled to use more expensive forms of transport .in order to effect early deliveries.
The Time Factor with Perishable Goods.
We have to deal also with large quantities of supplies which cannot be stored in bulk for long periods because of their perishable character. In the transport of such supplies the time factor is very important. Disregard of it may lead to a total loss of the supplies and will certainly lead to a depreciation in their value. A simple example of this fact is afforded by that common object, the egg. The market value of an egg, like that of a schoolmaster, is in inverse proportion to its age and experience. It starts life as a new laid egg, a thing now of considerable value. From this point it progresses downward through various stages, becoming is fresh egg, a cooking egg, and ultimately merely an egg, useful only for electioneering purposes. If too much of its life is spent in transport, it has reached one of the latter stages before it has arrived at its market. What then is needed is a rapid system of retail collection, working in connection with a sufficiently frequent system of through connection with the market.
z44 In the sphere of passenger work, the circumstances are not altogether dissimilar. Take, for instance, a small local branch line of a railway. If it is desired to work up the receipts of this branch, it is found desirable to run rail motors at frequent intervals rather than to run larger trains at longer intervals. The cost per passenger mile when the rail motors are used is doubtless greater, but the receipts are improved and ultimately, the traffic may be developed up to a point which will justify a frequent service of full-sized trains. On the other hand if, in the beginning, only one or two full-sized trains arc run in the day, the connection is so bad that the district never gets developed. This is obviously a case in which the use of the small unit is the best commercial policy.
Turning to the question of road traffic in towns, one finds, somewhat similarly, that the motor bus is more popular with the public than the tram, partly because it is a smaller unit. In this case, the smaller the unit, the shorter the delays that occur at stopping points." StipPosing the average passenger travels two miles and the capacity of the vehicle is 70 passengers ;then during every two miles in busy hours there must be delays adequate to allow 70 passengers to get off the vehicle and 70 more to get on to it. If the carrying capacity is 35 passengers this delay is halved. Moreover, if the smaller unit is employed, about twice the munber of vehicles are required to deal with a given volume of traffic. This means that the service is twice as frequent and, therefore, that the terminal delays of would-be passengers are roughly halved. From the passengers' standpoint, but disregarding differences of fares, the smaller the unit and the more frequent the service, the better.
Small Units Not Always Desirable.
The use of small units on the roads would not, how. ever, be justified if their presence involved a material. increase in congestion and obstruction. These constitute a charge on the community by slowing up all traffic and, therefore, increasing its cost of operation. Thus, it would not be sound policy to halve the carrying capacity of tramcars in order to make them more popular and to provide a more frequent service. The increase in the number of vehicles would certainly lead to an increase in congestion, which would cause a slowing up of the services and defeat the very object sought to be attained. Fortunately, however, the motor bus, owing to its flexibility, is so much less obstructive than the tram that, by its use, we can provide the more frequent service of smaller units without increasing obstruction at all.
Of course, if we were to increase the size of the unit in the case of the motor bus, we should reduce the Congestion of the streets or, alternatively, we should be able to deal with a larger volume of traffic at a lower cost per passenger-mile. Consequently, the new type of bus providing accommodation for about 45passengers is economically justifiable. If, however,
. . we were to go too far in the irecti in
on of cleasmg the size of motor omnibuses' we should have to face counterbalancing disadvantages in the form of lengthier delays at stopping places and, for a given volume of traffic, of longer delays before the arrival of the vehicle at the' point where the passenger is A fairly good example of the superiority of the smaller unit under many conditions is provided by the moving stairway as an alternative to the lift in cOnnection with the-underground railways. In effect, the moving ets.irway amounts to a contintious supply of small lifts. Each stair may be regarded as, a lift to carry one or two people. The delay before the-starting of the lift is reduced to. a negligible minimum. The delay in leaving the lift is non-existent. Consequently, even if the elevating speed is inferior, the effective speed is higher.
This rather desultory excursion around the fringe of a big subject will, it is hoped, at least be sufficient
tei show the futility o workinkOh the us'suiriptiOnthateither the bigger or the smaller unit is necessarily the better for every purpose. The:argument is often brought forward that trams must be superior to omnibuses because their capacity is greater and the cost per passenger mile is therefore, less. This does not follow in the least.' Everything depends on the value which the average member of the travelling public attaches to prompt conveyance and the &Void.anee of delays. Similarly, in respect of the carriage of goods, it is Particularly when prompt delivery is a positive asset that the motor vehicle must be used either as a supplement for the railway or else as an alternative to it, the selection between these two methods depending largely on the distance between the terminal points. It is only when the distances are considerable that the higher potential speeds possible on rails can really be attained.sufficieotly to lead to a saving of time on the journey,