The tracks on a full sized railway are not just laid at random. Every piece of main line, siding and loop that is laid has been put there for a reason. There are a number of reasons for the tracks to be placed where they are. The ideal is to have stations located in the places most suited to the passenger and freight traffic which will be using it and to link stations together with dead straight track which keeps running times to a minimum.
The main reason that this doesn't occur is because of restrictions caused by the terrain through which the railway line passes. The terrain will often require many long tunnels, cuttings, embankments, bridges, and viaducts if a straight line is to be followed. The cost of these features is very high and so a compromise is reached by curving the track so as to reduce the need for these features. Also land costs can result in stations being moved from their preferred location to one which is perhaps only second or third best.
These factors give us quite a lot of help when it comes to building a model railway. On our model railway we are basically trying to fit something that is long and thin into an area which is short and fat. The use of curves enables us to fit the layout into the available space and the use of tunnels and other features allow us to break up the layout into a number of separate scenes which are close together but represent places that are supposed to be much further apart.
There is another factor that affects the track arrangement on a full size railway and that is the operational requirements of the line. The number of main lines and the number and location of all of the sidings and loops depend on the amount and type of traffic that is using the railway line.
A model railway will be much more interesting to operate if these operational requirements are taken into account when the track plan is originally designed.
If you copy a prototype track plan and run the model to the exact same timetable as the prototype uses then all of your track planning has already been done for you. However, as soon as you change the amount or type of rolling stock that you are running then you really need to consider the effect that these rolling stock changes would have on the track requirements. Many (but by no means all) of the track plans that you can find in books have been based on prototype track arrangements and have been modified to fit a particular space (terrain restrictions) and perhaps also to allow for the increased frequency at which the trains will be expected to run (operational requirements). One of the ways in which you can develop a track plan to suit your own operational requirements is to start from a prototype or model track plan and to modify it to meet your own needs.
Another way to develop a track plan to suit your requirements is to start from scratch and design the track layout either completely yourself or by copying different parts of various model and prototype plans that you think are suitable.
Whichever method that you choose to develop your basic track plan the process of checking that operational requirements are met is exactly the same.
Let's start by considering the operational requirements of a simple siding. Figure one shows a trailing siding (ie. the train has to reverse in order to enter the siding). A train can quite easily leave wagons or coaches in such a siding by going past the siding, reversing back in and uncoupling the stock to be left, and then continuing on its way. A similar process is used to collect the stock which was left in the siding by an earlier train. This siding is able to be operated quite satisfactorily as it is.
The same is not true of a facing siding (figure two). Any attempt to leave stock in this siding will result in the locomotive being trapped in the siding between the stock and the buffers with no way out. Therefore only a train complete with locomotive (or a multiple unit or push-pull passenger train) can use such a siding. The operation of the siding to include its use for parts of trains (as with a trailing siding) can be achieved by adding a loop alongside the siding (figure three). With such a loop the locomotive can run around the train, shunt the siding as if it were a trailing siding, and then run back around the rest of the train so as to continue on its way. Note that in order to be able to run around trains the loop must be long enough to hold the longest train that you wish to be able to run around with enough clearance for the locomotive to be able to get past each end of the train as it runs around.
From this we can see that small changes in the way that your track is laid out can make a major difference in the usefulness of the various tracks from an operational viewpoint.
Next let us consider the situation with regards passenger trains. Passenger trains can
run non-stop through a station,
stop at a station and then continue on in the same direction,
pass another train travelling in the same or opposite direction, and
terminate and eventually return in the direction from which it came.
Each of these actions involves more of operational interest than the one before.
In the case of passing a passenger train straight through a station or stopping and starting again in the same direction, nothing is needed beyond having a platform alongside the track so as to be able to distinguish between the two alternatives. To take one train past another requires a loop to be added with either one platform between the tracks of the loop or a separate platform for each track. Note that in order to be able to take a train past another the both roads of the loop must normally be longer than the longest trains (including locomotives) that you want to be able to pass. There are ways to pass two trains when the loop is shorter but the moves are fairly involved and you don't want to have that complication every time that you want to pass two trains.
The passenger train movement of greatest operational interest is to terminate the train and set back out in the opposite direction. This can be done on a through platform or on a terminal road, the two situations require the same track layout only in the case of a through line the track also continues on in the other direction. Operationally the two situations are slightly different in that a terminating train usually needs to occupy a platform for much longer than a through train and if it is occupying a through road then no through trains can use that road until the terminating train has moved back out. Therefore it is preferable to terminate trains on a separate terminating road.
Let us now therefore consider a simple terminating road (figure four). A passenger train can quite successfully be terminated on a single track like this but, unless it is a multiple unit or push-pull, the locomotive will be on the wrong end of the train for the train to be able to depart. There are two ways to solve this problem. The first solution is to use a different locomotive on the train when it departs. To be able to do this requires somewhere for the second locomotive to sit clear of the main line until after the train has terminated. This can be done most simply by providing a short loco siding just beyond the end of the platform (figure five). Once the train has arrived at the platform the locomotive is uncoupled. The locomotive in the loco siding is then attached to the other end of the train and the train is ready to depart. Once the train has departed the other locomotive can run down the platform into the loco siding.
The other alternative involves using the same locomotive on the departing train as was on the train when it arrived. This requires the provision of a loop (figure six). The locomotive pulls the train into the platform clear of the ends of the loop. It is then uncoupled and runs around the train. The locomotive is then coupled to the other end of the train ready to depart.
A terminus on the end of a section of double track has further problems. Normally each platform will be used for both arrivals and departures. This means that each platform road needs access to both of the main lines. This can be provided by the use of two crossovers (figure seven). Note that a loco siding (if that method is being used) must be beyond these crossovers so that it too may have access to all tracks, alternatively each track can be provided with its own loco siding but that requires a larger number of locomotives. Figure eight shows an alternative arrangement where the two crossovers overlap. A single crossover between the two roads provides for the release of locomotives in the same way that a loop does for a single platform provided that only one platform is occupied by a train at the time. For very busy terminii a central escape loop attached to both platforms can be provided.
Additional platform roads can be easily added at both single and double track terminii. For double track terminii the extra tracks should join the main lines between the end of the platform and the crossovers so that access to the platform for both arriving and departing trains can be provided. A platform road attached beyond the crossovers may be useful for a parcels bay where (depending on which side it is on) the parcels train can arrive (or depart) directly but must be shunted via another platform road for departure (or arrival).
Goods yards can be as simple as one or two sidings (or more) trailing the main line (figure nine). A trap point (optional on the model) protects mainline trains from breakaways in the siding area. To shunt sidings like this requires the use of the main line track and hence no through trains can run until after shunting is finished or if the through train must run before that the train being shunted must be moved clear of the main line and held until after the through train has passed after which shunting can continue. This will not be a problem on branch lines but you will normally want to keep trains moving on the main line. Another problem is that, despite having a crossover from the other main line, this yard is effectively one directional since no loop has been provided to allow trains from the other direction to be run around so that they can be shunted.
Figure ten shows a goods yard where these two problems have been solved. A headshunt is now provided so that the sidings can be shunted without blocking the main line. By attaching the headshunt as shown we no longer need a trap point since the turnout into the siding nearest the main line now serves that purpose. Also by running into the headshunt rather than one of the sidings economises on track since to be able to back into a siding and then run forward into the headshunt would require a minimum of a train length of clear track in both the siding and the headshunt whereas by running straight into the headshunt only the headshunt needs to be clear. The yard also now serves both directions through the provision of two crossovers between the main lines with the distance between them serving as a loop. With the arrangement shown it will be the trains on the main line nearest the yard that will need to be run around in order to be able to be shunted while trains from the far track will simply need to be reversed across one of the crossovers onto the other track and can then be run forward into the headshunt (and vice versa when leaving).
This second arrangement only ties up the main line when a goods train is arriving or leaving. This time could still be quite substantial because of the need to run around or shunt backwards and forwards to get in and out of the yard, also these maneuvers block both main line tracks while they are taking place. This will not be a problem on many layouts which only have enough room for one train on each main line anyway and hence only one train which will be held up for a short while.
Larger goods yards can solve even these problems. In figure eleven we have a quite substantial goods yard with sidings running off in both directions. The headshunt is replaced by a loop between the two sets of sidings which serves as a headshunt for both sets of sidings and also allows wagons to be run around within the yard itself (which will need to happen far more frequently because the sidings go in both directions). The direct connection between the left hand end of the yard and the far track allows goods trains from that track to be reversed straight into the yard without all of the backward and forwarding required of the previous arrangement.
Each of these yard arrangements is prototypical and where each is used depends on the operational requirements of the particular prototype. Whichever yard arrangement that you decide to use, the next step is to determine its location with respect to passenger platforms (if any) at that station. In all cases the platforms can be located beyond the yard at either end or can be located alongside the yard (between the crossovers on yard arrangements having a loop). This last location saves on length and also where crossovers are provided allows for the reversal of passenger trains as well.
Locomotive storage and servicing is the next thing to be considered. Locomotives can be stored on open tracks or can be held in a shed. In either case the track layout will be the same. Steam locomotives require coal, water, and ash facilities as well as a turntable so that tender locomotives may be turned. Diesel and electric locomotives require fewer facilities and can have a simpler track arrangement.
Figure twelve shows a simple loco depot for steam trains. The lower siding can be a raised track used for coal delivery. Locomotives arrive on the next track where they pass over an ash pit before being coaled and watered. They then run onto the turntable where they are turned. The locomotive leaves the turntable via the other line and is reversed into the shed. When the locomotive is required it can pull straight out of the shed and leave the depot.
An alternative arrangement found in some countries would be to provide a roundhouse next to the turntable thus saving on the turnouts leading into the shed. This arrangement should still have two access roads onto the turntable since we do not want to have to run locomotives back across the ash pit in order to get them out. Alternatively the ash pit and coaling facilities may be provided on a separate line or even be entirely separate. This arrangement has the disadvantage that the turntable needs to be used to get locomotives out of the shed as well as for turning them. This can be a major disadvantage on an exhibition layout if the turntable breaks down.
A solution to this problem is to use a through shed (figure thirteen). This arrangement operates the same way as the second alternative until the locomotive has reached the shed. It then operates the same as the first alternative when you take a locomotive from the shed.
A locomotive depot is a particularly useful feature to have at a terminus station since it is here that trains will need to be turned most often. The simplest way to attack one of these depot arrangements to a terminus is to attach it in place of the loco siding (figures five and seven). This will enable operation of both the terminus and loco depot in the manner previously described without requiring any additional turnouts to attach one to the other. Alternatively the depot can be attached anywhere via a single turnout provided that the locomotives can reach the departure end of the station without having to travel along a platform road.
A final feature to look at from an operational viewpoint is the junction. Operationally a junction is the same whether it be between a main line and a branch line or simply a bay platform at your through station.
A junction can be a single track coming off of a single track line, in which case only a single turnout is required.
A single track branching from a double track main line (whether for a branch or a bay) can be done in two ways. The first way is shown in figure fourteen. Here the single track comes off of the near track while a trailing crossover provides access for traffic from the single track to achieve the correct line on the main. For branches going off in the other direction either a facing crossover is needed in place of the trailing one (something many railways try to avoid wherever possible) or the alternative arrangement (figure fifteen) can be used where the single line is attached directly to both main lines.
Double track junctions can also be done in two ways. Figure sixteen shows the standard arrangement for a double track junction using two turnouts and a diamond crossing. This arrangement has one disadvantage in that there is no facility for a train approaching the junction from the trailing end to be able to reverse and travel down the other line. To be able to do this a separate reversing facility would need to be provided at a nearby station.
The second alternative for a double track junction is shown in figure seventeen. It is now much more obvious which is the main line and which is the branch. This arrangement allows trains to reverse direction at the junction but does not allow a train entering the branch to pass one leaving the branch. This arrangement is suitable for use where the branch tracks are bay platforms and hence are relatively short. The arrangement is also used prototypically in some modern junctions where multi-aspect colour light signals allow for close spacing of trains.
By combining these various track arrangements, a layout capable of much varied operation can be produced. Such a layout should be able to be operated much easier than one for which such planning has not taken place. This does not mean to say that all operations will be able to be carried out in a straightforward manner. What it does mean is that enough different moves will be able to be made in a simple yet realistic way for the operation to appear real. No more simply running trains round and round on the main line and just using the other tracks for storage because it is so complicated to make any other move that you get fed up of trying to do it. Yes, storage tracks can be added to wherever seems appropriate on the layout, but operational tracks are also required if interest is to be maintained.
Complicated moves can still be carried out on the layout but they happen when you want them to not just because that is the only way to be able to do something. They can be done to add interest to operation rather than having to be done so frequently that they become frustrating.
An example of a complicated move that can be readily created on any single track layout is to run two trains both of which are longer than your normal train length and hence cannot fit in your loops when it comes time for them to pass. Then you can have fun shunting them past one another. A not quite so complicated problem on a double track line is to have a longer than normal goods train needing to shunt a facing siding or yard.
In any case, more thought given to the operation of the layout during the track planning stage will pay off in a more varied operation once the layout is built.