In the fourth part devoted to itineraries, we saw what the advantages of flexible transit could be compared to rigid transit. In this fifth article, I propose to deepen our study which will then allow us to build automatic systems capable of managing flexible transit while passing in a station.
Note : that the writer of the article is from France and therefor uses French themes, signals, and equipment. The names and initials used in the pitchers and diagrams are kept the same for practical reasons but are explained in English through out the article
Issues with station transit
Station transit raises several difficulties related to the specific characteristics of rail traffic in stations:
- Some trains stop at the station,
- Other trains cross the station without stopping (e.g. freight trains or fast trains that do not stop at medium-sized stations)
- Still others can arrive in one direction and leave in the opposite direction (Railcar, shuttle for example)
- Maneuvers can be carried out in stations (traction relay or reversal of the direction of travel for the same convoy)
The fourth part on the routes has enabled us to know how to safely manage rail traffic on a station siding or an area of multiple switches, but we limited ourselves to taking into account fluid traffic without train stops, maneuvers or change of direction.
In this study we will see how to adapt flexible transit taking into account the specific characteristics of traffic management while in stations.
First of all, I would like to emphasize that achieving flexible transit regulation, even for a medium-sized station and even limiting oneself in the number of routes to be carried out, is a difficult task, not that it is a high-level intellectual exercise (a good dose of common sense and logical thinking is enough) but because the route chart and the management of the approach light signals are complex. A very precise inventory of the possible scenarios must be carried out beforehand in a very meticulous way before starting the construction of the automatic management system.
We will see in detail below all this preparation work, especially for signal management.
The transit station
The model I am proposing is based on a fictional transit station with 5 tracks on the platform. I named it Fleury-en-Beaujolais station. A main track crosses the station and allows the passage of main line trains without stopping.
The station is supposed to be somewhere between Paris and Lyon. Coming from Paris, that is to say coming from the west, we only have the main line with its 2 lanes, even and odd.
To the east, in other words towards Lyon, the line is divided into 2 divergence. The first, which is located downstream of the station, which we will not take into account in our study. The second with a single lane, called lane 3, towards Dôle. This destination appears on the photos below.
Photo 2 shows us the west exit of Fleury station towards Paris. The main traffic lanes (Paris – Lyon line) bear the numbers 1 and 2. Traditionally I have kept the Sncf numbering which assigns an odd number to the lanes coming from Paris and an even number for the lanes going back to Paris. Here 1 for the route coming from Paris and of course 2 for the Lyon-Paris direction.
In the station, the tracks are numbered from 1G to 5G, tracks 1 and 2 becoming 3G and 4G respectively in the station.
To the east, the appearance of the station is quite different.
Indeed, we find at the exit towards the east the junction towards Dôle (path 3).
Note at the exit from lane 1G, on the left, 2 dead-end service lanes. In the management of routes, we will not take into account these 2 lanes or the switch which allows the movement of convoys to be switched to these 2 dead-end lanes.
These service roads will have their place in a future article which will be devoted to shunting in stations.
From now on we can see that we are in the presence of a medium-sized station. Nothing to do with the entrance or exit beams of Lyon-Perrache station (see this article). However, configuring the automatic route management system will be a difficult exercise for us.
The figure above shows us an overview of the station. On the left, on the passenger building side (BV), a railcar is parked on track 1G while on track 5G a second railcar arrives from Lyon.
The tracks of the main line allow the crossing of the station at high speed, no switch being crossed in the deviated position. The 1G, 2G and 5G tracks, for their part, require the crossing of switches in the deviated position. This constraint of course has a direct impact on the type of signal installed at the entrance to the routes.
The following figure shows us the optical control panel (TCO) of the station:
For each track switch, the number of the switch (green background) and the number of the switch interlocking relay (REA) on a red background are indicated nearby on the TCO.
All service roads are two-way. Tracks 1 and 2 of the main line are one-way, including in the station (3G and 4G tracks). Normally the 3G and 4G tracks should be accessible in the opposite direction to allow any type of maneuver necessary (Taking charge of a broken down locomotive for example). As in EEP the trains never break down we will do without this possibility. More prosaically, this will spare us the programming of several additional routes because, as you will see, we will have plenty to do with those we have selected.
Important : An essential principle that is valid in everyday life in many areas states : There are no complex problems that can not be broken down into simple solutions.
I do not know if this adage can be applied in all circumstances but it seems to me to be perfectly appropriate in our situation.
Indeed, as far as we are concerned, we have a station crossing with 2 beams, one to the west and the second to the east for trains traveling in the west-east direction. For trains traveling in an even direction, we will obviously have the opposite east-west diagram.
We know how to manage routes on a single beam as we saw in the l’article dedicated to flexible transit. So let’s break down our station beam into 2 simple beams: (groupings)
- Zone 1 beam to the west.
- Zone 2 beam to the east.
The division of the station grid into two zones of routes leads to treating each route not as a global route programmed in a single sequence from the entry point to the exit point but as 2 successive routes treated as far as possible as independent routes .
In other words, this means that the management of the entire route for a train crossing the station without stopping there will be done in two stages :
- For example, the approaching train on track 1 West calls the Automatic Route Management (AGI) to allow routing only in the West beam.
- Once the western route is executable, the AGI establishes the route of the exit route in the East zone, between the station exit and signal 31, this time in the East beam.
This two-step programming is actually more complex than it first appears. In fact, the 2 phases set out above can only take place as is in so far as the routes requested at the entrance to zone 1 West, as well as at the exit from zone 2 East are immediately executable as soon as no itinerary incompatible with those requested is running in each of the two zones.
So let’s go back to the route call for Zone 1 West and now consider that there is an incompatibility. The train will therefore be stopped at square signal 30 (stop signal) as long as the incompatibility persists.
In this case, the activation of the exit route in zone 2 would be aberrant because it would lead to blocking the realization of other routes in this same zone 2 while the train is stopped at the entrance to the West zone. Such a design in the programming of routes would inevitably induce a significant loss of traffic fluidity, especially in the case of stations with high traffic density.
This means that routing in the exit zone can only be done if routing in the entry zone has been activated.
Important : In other words, for trains that do not stop at the station, the establishment of the exit route is strictly subordinate to the establishment of the entry route.
The flowchart below in Figure 7 illustrates this principle :
In the sequence of establishing a route having zone 1 as entry and zone 2 as exit, the AGI (Automatisme de Gestion des Itineraries = Route Management Automation) will first process the compatibility of the ITN (itinerary / route) requested only for zone 1, then if this operation authorizes the establishment of the entry route, the automated system then processes the exit in zone 2 for trains crossing the station without stopping.
For trains stopping at the station, the problem does not arise. The AGI will check if the train should stop at the station. If this is the case, the procedure for switching on and establishing the route is immediately carried out.
The table in figure 8 gives us the 2 possible scenarios :
- Either the route requested provides for a stop at the station and in this case only the route establishment procedure in Z1 is initiated. The exit procedure in Z2 will be launched later completely independently of Z1.
- Either the route does not include a stop at the station and in this case Z1 is processed first. If ITN2 is activated in the Z1 beam, the automation then activates the similar procedure at the Z2 exit. In other words, the exit in Z2 is subject to the establishment of the route in Z1.
This flexibility has the double advantage:
- To allow the train to enter Z1 even if the exit ITN in Z2 is not available. The train will then be stopped at the station pending the opening of the requested route.
- Not to unnecessarily block the other routes in Z2 in the event that the ITN in zone 2 is free and therefore engaged while the ITN in Z1 is unavailable. We suggest a curious traffic management since a train stopped in Z1 due to incompatibility would block any route in Z2 while itself would not be able to enter Z2.
As I indicated above, the management of routes in two distinct zones makes it possible to a certain extent to process a request for a route in 2 stages as if these routes were completely independent of each other. This is strictly correct for trains stopping at stations. For trains in transit without stopping, this statement should be qualified in so far as the management of approach signaling can not in any way be handled realistically without integrating the combination Z1 and Z2 simultaneously. This is undoubtedly the major problem of station transit programming in EEP, which deserves detailed development.
Reminder on signaling
We will deal in this paragraph only with signaling for entering the station by track 1. It is quite obvious that the problem posed and the answers given are identical for entering zone 2 East, both by track 2 and by the lane 3.
Let’s first look at the west entrance beam of the station:
Figure 9 shows us the entrance to Z1 West. Although the entrance is very simple with a single entrance lane (Lane 1) and a possible distribution on 4 lanes in the station (V1G, V2G, V3G and V5G) we will quickly see that the programming of the signals is nonetheless very complex.
First, let’s do a short reminder of the types of light signals in play here.
Our entry beam has a direct Route 1 -> 3G route requiring no slowing down except for that imposed by the possible stop at the station.
For the other routes, the trains pass one or more switches in the deviated position. We will agree here that the crossing can be carried out at 60 km/hour. It is therefore necessary to implement a 60 km/h slowdown coupled with a slowdown reminder at the entrance to zone 1 of routes.
Note : that the writer of the article is from France and therefor uses France signaling equipment. Although they may differ from what you are use to the idea and principals remain similar
First the announcement signal. This (Fig 10) is a type F signal, located at the entrance to the block preceding the route entry signal. In this case, the signal displays free track. This would be the case for trains approaching and having to cross the station in a direct route via track 3G.
The execution signal which is at the same time the route entry signal is a type G signal (Figure 11). By default, in the absence of any route call, this signal is squared,( stop position) i.e. it displays 2 red lights.
Only a route call will open this signal, which will then display the appropriate status according to the chosen route.
In our present network the signaling device is therefore as follows:
- 102.Signal 102: signal with 3 automatic block lights in free track position (VL).
- Signal 33: slowdown announcement signal 30/60
- Signal 30: route entry signal for the West zone Z1
- Signals S 20 – S 21 – S 22 – S 24: station exit and route entry signals in the East zone Z 2 respectively for tracks 1G, 2G, 3G and 5G.
- Route call contacts located just at the entrance to block c102.
Concrete case 1
Let us now see a first scenario. In this case a train has just entered block c102 calling the route V1 – V1G:
The train is in block c102. Signal S 102 is closed. The requested route being immediately executable, the route is displayed on the TCO. Signal S 33 displays the slowdown announcement and S 30 displays the warning in addition to the slowdown reminder, which is completely normal since the ITN Z2 signal (S 20 here for track 1G) is closed.
Here we are faced with a simple scenario.
Let us now see with figure 14 below what would happen if the route V1 -V1G was not executable immediately:
- S 102 is closed after the train has passed, which is completely in order.
- S 30 is squared since the requested route is not accessible.
- S 33 announces the slowing down since the route requested is on a deviated track but also displays the warning telling the driver that the next signal is closed.
During this time, the automation is running and performing a compatibility check on the route line V1-V1G each time the mobile route switch (CMI) is passed. For a reminder on automation, you can review this article.
When the route which prohibits the requested interlocking is freed, the automation then interlocks ITN V1-V1G, positions the switches and opens the signals in the appropriate state.
Two scenarios are then possible:
- The train is still in block c102 and we are returned to the signal display as shown in figure 13 above.
- In the meantime, the train has passed through block c33 (that it straddles c102 and c33 does not change the problem).
In this second case, if the programming of the route does not take into account the position of the train, we end up with a flagrant anomaly in the display of the announcement signal S33:
S33 is open at idle. In concrete terms, as figure 15 clearly shows, the safety at the rear of the train is no longer ensured. So what happened? the explanation lies in the fact that the management automation as we have designed it only knows 2 possible states:
- The route is unreachable and the signals display the states as shown in Figure 14 above.
- The route is immediately feasible and then the AGI switches the signals to the states displayed in Figure 13 without worrying about where the train is. We then obtain an untimely operation of S33.
To obtain a display that conforms to reality, it is therefore important to know where the train is in the event of delayed activation of the requested route. This therefore requires integrating a device that will detect the position of the train at any time to allow correct display of the signaling. In the present case, the AGI must in no way act on signal S33 once it has been passed by the convoy.
Thus figure 16 shows the exact signaling configuration in the present case:
- Signal BAL S102 is on warning
- The train has just crossed S33 putting this signal to the semaphore
- The ITN entry signal is idle doubled with the warning that announces S20 squared.( stop signal)
We now have signaling that ensures the safety of the train. Signal S33 is closed and thus protects the rear of the convoy by preventing any risk of overtaking by a second convoy.
Concrete case 2
Let us now consider a second scenario. Take the case of the V1 – V3G route. This is a direct route and does not require any slowing down in the absence of switches in the deviated position. Trains are allowed to pass through the station at the maximum speed of 120 km/h due to a speed indicator board (TIV), not shown here in the diagram below, located in block c33:
Figures 17, 18 and 19 show us the display of the signaling as the train progresses from block to block, both in the approach zone and in the Z1 route transit zone. There for. It is these signaling states that S30 and S33 must imperatively display in the event of delayed opening of the exit route in Z2 East:
Important: Determining the position of the train is essential in the management of transit in the station. Failure to take it into account inevitably leads to anomalies in the management of rail traffic.
Let us now examine a specific scenario which will show us the malfunctions to which we would be exposed if the position of the railway convoys were not taken into account.
To do this, let’s use a second train, a railcar heading towards the V1G track at the station. He called the V1-V1G route but the train preceding it forbade its opening due to incompatibility. The railcar is therefore stopped at the route entry signal S30.
Meanwhile, train 1 entered the V3G section at the station. However, he has not yet released all of the switches and crossings on his route, which prohibits the programming of the V1-V1G route in favor of the railcar (Fig 20):
We have so far here a perfectly normal operation of the automation of route management.
The following sequence illustrated by figure 21 shows that train 1 has released the Ag 7 switch, marked in the red circle. Now nothing prevents the formation of the V1-V1G route. During this time, train 1 continued on its way to signal S22, which still remained closed due to incompatibility with another route leaving station Z2, regardless of which route.
Figure 22 below shows us the logical sequence: the incompatibility having disappeared, the route of the railcar is traced. The S30 signal opens displaying the slowdown with a warning since the railcar must stop at the station. The signage is therefore fully consistent.
Here everything goes normally without the slightest error and can therefore make us believe that our programming is perfect.
In fact, this is not the case because the illusion is due to the fact that the ITN of train 2 opened before that of train 1, thus allowing the formation and opening without error of the route requested by the train. railcar.
Let us now return to the situation as it appears in figure 20 and that, contrary to what we have just seen, it is the exit route in Z2 of train 1 which opens first. If we do not take into account the exact position of the train then we obtain the signaling configuration as it is displayed in figure 23 below:
The error stems from the fact that the AGI established the route V1 In-V3G-V1 Out without taking into account the position of train 1 at that time. As a result, he switched the signaling as if the train was still in the ITN calling area at c102, so with signals S30 and S33 IN FRONT of the train, except that in this case S30 and S33 are BEHIND train 1 .
This leads to a huge programming error with three serious anomalies:
- The railcar is routed to V3G instead of V1G which was its originally assigned destination.
- The rear protection of train 1 is no longer ensured and the risks of overtaking by train 2 are high.
- The protection of train 2 is no longer ensured with the signal S33 being green.
This observation imposes on us the urgent need to set up a train presence detection device for each block of the approach zone. The exact location of the train will authorize or prohibit, depending on the case, the change of state of signals S30 and S33.
We will see in the part “Practical application of flexible transit in stations in EEP” how in the “mechanical” version it is possible to concretely carry out lane detection. In this case, we will use invisible “Stop – Start” type signals for this, corresponding perfectly to the two logic states that are:
- Block free.
- Block occupied.
The next article well not be limited to the singling problem of station transit signaling but deals with all the important points to achieve a reliable automation, capable of managing heavy traffic in a passing station.
This article is now complete. If you have any questions or suggestions, please give us your feedback in the leave a reply input box below.
Thank you for your helpful comments. Have fun reading an other article.
This article was translated by Pierre for the English side of the EEP-World from the article written by François for the French side of the EEP-World.