The New Zealand Railways Magazine, Volume 1, Issue 6 (October 24, 1926)
Modern Shunting Methods — Part V.—Dimensions and Arrangement of Marshalling Yards
In considering the dimensions of a marshalling yard it is important to observe that not only must normal traffic be dealt with expeditiously, but an adequate margin should be provided to enable sufficient elasticity of movement to overcome and rectify any dislocation and delay caused by unexpected rushes of traffic.
Unfortunately it appears to be the exception rather than the rule for yards to be too large for normal traffic. A yard that is above requirements can be worked economically and is a wonderful safety valve in times of congestion, but a yard that is too small is always costly and can never be economical. Shortage of accommodation necessitates a large number of unnecessary movements both of engines and wagons. Further, a yard working at full pressure cannot immediately overcome any delays which may arise. Hence these are extended over a considerable period and react adversely upon the general organisation of train operation. Any disturbances in this connection have far reaching effects and immediately increase the operating expenditure.
The matter, therefore, resolves itself into a question of efficiency and economy in operation versus considerations of finance. An efficiently operated yard is an economical one, for efficiency depends on reducing conflicting movements to a minimum. The officers responsible for the lay-out have to decide whether it is advisable to be committed to a large capital cutlay and consequent heavy interest charges and a low operating cost over a number of years—not only in the yard itself, but in the indefinitely large area that is advantageously affected by a well regulated and rapidly operated yard—or whether to follow the more conservative plan of providing a less ambitious scheme, trusting that the operating expenses will, in actual practice, be less than estimated, and that all the difficulties that might arise in the future could be overcome by a small expenditure for increased facilities from time to time.
Coming to the technical side of accommodation and general arrangements, it is plain that whatever the method of shunting employed the component parts of a shunting yard are the same, viz:—
1. Reception roads.
2. Departure roads.
3. Marshalling and sorting.
4. Storage roads.
The provision of subsidiary requirements, such as:—
Loco, Depot and run round roads.
Wagon repair Depot.
Refrigerator car service.
Wagon cleaning sidings, etc.
These vary according to location, general purpose of the yard, the nature of traffic dealt with, the extent to which facilities are provided adjacent to the yard, etc.
With regard to reception roads, the number of roads vary according to the traffic density. One of the main factors is the length of tablet sections and, in the case of signalling, the headway permitted between trains. It too often happens that the sidings are not sufficient to take the trains as they arrive. That is to say, the shunters, through lack of facilities or lack of time, cannot take a train from the reception roads and break it up before another arrives. There is, therefore, a very close relationship between the main line operation and yard facilities. It is true where the density, is not particularly high, the timetable can be arranged to suit the yard work, but this, is invariably an unsatisfactory means of overcoming difficulties, in that other yards must suffer and possibly, in these days of competition, the rigidity of a timetable influenced by yard operation might adversely affect the revenue. It is essential, then, that the reception sidings be designed to so cope with the traffic offering that main line operation is not in any way interfered with or handicapped by the capacity of the yards.
The length of the roads should be such that the longest trains can be accommodated.
In the case of one group of reception sidings common to both up and down traffic, it is desirable to so arrange that entry from both ends is done with the least possible interference with legitimate yard work. The running roads should not be confused with shunting roads. This is in the interests of smooth working and, page 25 above all, safety to the staff. The larger the yard and the greater the volume of traffic, the more necessary this becomes.
It is not always a simple matter to decide where the siding shall be when traffic from both directions has to be considered. In addition to easy access from the main line the question of reducing unnecessary movement of wagons from these sidings to the marshalling yard has to be taken into account. The desideratum is to reduce the amount of return movement wagons have to make in the yard. For this reason, therefore, the sidings are usually placed at the head of the marshalling yard so that only wagons arriving from one direction have a return movement. Reception sidings can of course be incorporated in the main body of the yard, but it is found a much better practice to keep them separate. This reduces the interference with yard working and enables shunters, wagon examiners, number takers, etc., to move about more easily, and is generally more satisfactory.
Departure Roads,—These roads are set aside for trains made up in marshalled order awaiting departure. They should be long enough to take the longest trains leaving the yard. The number of roads depends upon the accommodation of the yard; the speed at which trains can be received, marshalled, and made up in train order; and the capacity of the main line for receiving the trains at the-periods when the marshalling yard is working at its maximum. As in the case of reception sidings, the departure sidings should be detached from the marshalling, so that the yard staff connected with the despatch of trains can work undisturbed.
Direct departure without interference with ordinary yard work and (in the case of double main lines) direct connection to the main line without fouling the opposing line is very necessary in busy yards. As previously explained the location of the yard in relation to the main line has a bearing on this matter. Burrowing or fly-over junctions are resorted to when traffic warrants them.
Easy access for the train engines from the Loco. Depot or from arrival roads (if necessary) is essential. The departure roads should be so placed in relation to the sorting roads as to enable trains to pass from one to the other with the least amount of shunting movement.
Marshalling and Sorting Sidings.—Separate groups of these are advisable for each direction when the traffic in each direction is more or less independent of the other, otherwise a single group is preferable.
Marshalling.—As regards the number and capacity, the most important question is to decide in what form the first marshalling is to take place, for this decides the number of roads. That is to say, how is the separation of wagons to be made? By destination? By direction? By group page 26 or region? By class of train? Must each be made separately, or can all be done at the same time with one forward movement? The main object of the first marshalling is to break up a train into the greatest number of component parts in the shortest possible time. The greater the number of roads the casier can this be done. There must, of course, be a limit to the number of roads radiating from one shunting road, whatever method of shunting is employed. In an engine worked yard the limit is fixed by the number of roads an engine can economically and expeditiously work. In a gravity yard, with the most modern form of shunting appliances, as many as 60 roads can be operated from one gravity road. Beyond this number difficulty would be experienced in arranging a gravity shunting road sufficiently steep to send wagons to the further parts of the yard, yet, not so steep as to cause violent collisions between wagons running into the sidings nearest the gravity shunting road.
The accommodation to be provided can only be decided through the officers responsible being conversant with the density of traffic, the number of destinations, local conditions, make up of trains and the peculiarities of goods train loading, etc. It is, therefore, quite impossible to lay down any hard and fast rule capable of general application.
If a yard is serving a large centre, roads will be allocated to private sidings, goods sheds and yards, wharves, etc; if located to concentrate and marshall traffic for numerous directions, the directional method will apply; if there are other yards in the vicinity necessitating further shunting, the regional system suggests itself; if fast through trains conveying special traffic long distances, i.e., coal, grain, etc., the classification by train would be advantageous. As just stated, the matter is too complicated to express in general terms and any suggestion as to the method to be employed would be valueless. In New Zealand such complication will not arise for some time, and the method of classification is comparatively simple, there being three general classifications (1) destination, (2) points at destination, (3) points beyond the sub-terminals at which trains leaving the yard are re-sorted.
It is advisable to plan the lay-out of the marshalling sidings so that trains can depart from them if necessary. This allows a certain flexibility in working which is advantageous at rush periods.
To be continued.