For most passengers, underground transport remains a mystery hidden behind the concrete walls of the tunnels. We usually enter the car, take seats at the door or in the center of the cabin, watching only the flashing of advertising and lights in the dark. However, few people think about the complex engineering process that allows heavy trains to change the direction of movement at the end station. This maneuver seems magical, but it is actually the result of a clear coordination of automation and human actions.
The process of changing direction, or rolling stockIt requires the highest precision. A train cannot simply turn 180 degrees like a car on a wide road, because it is rigidly tied to a rail track. To implement this maneuver, complex track development is being built at the end stations and in the depot, including turnouts and additional branches. It is these engineering solutions that allow you to change the vector of movement of the composition without losing time for long downtime.
In this article, we will discuss in detail the technical aspects of how the reversal occurs. You will learn about the different station schemes, the role of switches and how the driver manages this process. Understanding these mechanisms will help you look at the usual trip in a completely different way, evaluating the scale of the infrastructure hidden from the eyes of the average passenger.
Basic principle of rolling stock turnover
The fundamental problem of railway transport, including the subway, is that cars do not have steering in the usual sense. Wheel pairs are rigidly fixed in trolleys, and trolleys - in the body of the car. Therefore, to change the direction of movement, it is necessary to physically shift the rails or overtake the composition along a special loop. In conditions of dense urban development and deep tunnels construction of loops is often impossible, so engineers use the switching.
Hand-shifting is a track device that allows you to transfer rolling stock from one path to another. When a train arrives at the terminal station, it must not just stop, but take the opposite route. To do this, an arrow is installed in front of the composition, which transfers it to the neighboring path. After that, the driver moves to another cabin (or the control panel switches remotely), and the train is ready to go in the opposite direction.
There are two main types of turnover organization: with and without changing the direction of the train. In the first case, the locomotive or head car that led the train is in the tail, and the driver must drive it to the beginning. In the second case, which is more common in the modern metro, the train has control cabins on both sides, making the process much easier. The key element here is stationeryIt determines how long the whole procedure will take.
⚠️ Warning: Never attempt to lock doors or interfere with automation at end stations. Any delay in the cycle turnover It can disrupt the entire line, causing a chain reaction of lateness.
Modern automation systems, such as GoA 3 or GoA 4They allow some of these operations to be performed without human intervention. The computer itself controls the opening of doors, transfer of arrows and even the movement of the composition on the way of departure. However, even in fully automated lines, dispatchers centrally manage the flows, ensuring security.
Train turning station schemes
Engineering thought has developed several basic station schemes that allow the efficient deployment of trains. The choice of a specific scheme depends on the passenger traffic, the geology of the soil and the availability of free space underground. Each scheme has its advantages and disadvantages in terms of throughput and time required for maneuver.
The simplest and most common scheme is single-stage. In this case, behind the platform there is one additional path where the train is driven. While one train is on the platform and lets out passengers, the next one is already waiting in a dead end or approaching him. After disembarking passengers, the doors close and the train hits a dead end, freeing up the main platform for the next train.
More complex schemes suggest that cross-conference in front of or behind the station. This allows trains to change direction without going into deep dead ends, but simply moving from one main path to another. This is often used on lines with very high passenger traffic, where every minute of downtime is critical. It is important to accurately time the arrows.
- 🚇 Ring pattern: The train does not turn around, but goes in a circle, changing only the side of the passengers boarding (used on ring lines).
- 🚇 Two dead ends: Allows one train to sink while the second takes up the platform, which increases the intervals.
- 🚇 Cross-conference scheme: Allows you to make a turn without running into a dead end, just going on a parallel path.
In some cases, especially in the old metro, a scheme with the turnover of "loops" is used. The path behind the station makes a full loop, and the train, without changing the direction of the head part, returns to the platform of the opposite direction. This is rare, as it requires a large radius to turn.
⚠️ Note: When using a cross-section scheme, the speed of the arrow is limited. The train always passes this section at a reduced speed, which can feel like a light vibration.
What is the "neck" of the station?
A neck is a complex section of the path in front of or behind a station where several paths converge or diverge. It is here that the maximum number of turnouts is located, and this is where delays in maneuvers most often occur.
Role of switches and automation
The heart of the reversal process is the switching. These are complex mechanical devices consisting of wags, frame rails and a transfer mechanism. When the train is approaching the end, the system signaling and centralization (SSC) receives a command to prepare the route. The arrows must be put in the right position long before the composition approaches.
In modern metros, this process is fully automated. Sensors on train wheels (accelometers and wheel pair counters) transmit location data to a central computer. As soon as the tail of the composition frees a certain section of the path, the system gives a command to translate the arrow. The driver in the cockpit sees on the screen display permission to move or command "Stop".
The mechanical part of the arrow translation takes a few seconds. The electric drive moves the wig, which is pressed against the frame rail with great force so that the wheel can not jump off. If at least one arrow in the route does not stand in the correct position or is not fixed, the traffic light signal for the driver will remain red. That's the basic principle. safety.
| Type of device | Function | Time of operation | Controlling |
|---|---|---|---|
| Electrical arrow | Translation of witty | 2-4 seconds | Automatic. |
| Rail chain | Defining employment path | Instantly. | Permanent. |
| Traffic light | Permission/Prohibition of traffic | 0.5 seconds | Automatic. |
| Stress (buffer) | Stopping the lineup at a deadlock | - | Mechanical |
It is important to note that the shooters require constant maintenance. Dirt, ice or foreign objects can disrupt their work. Therefore, in winter or after thunderstorms, you can often see track workers at the end stations, checking the state of the mechanisms.
If you are sitting in the first carriage, you may hear a characteristic click or hum before stopping on the final. This works the arrow mechanism, preparing the way for your train.
Actions of the driver during turnover
Despite the high degree of automation, the driver remains the main guarantor of safety. His work at the end station is a well-established algorithm of actions, which he repeats dozens of times per shift. After arriving at the terminal platform, the driver must make sure that all passengers have left the carriage.
There is a procedure called circumvention. The driver must walk along the platform or in the cabin (depending on the rules of the particular subway), making sure that no one is left in the car, especially sleeping passengers or children. Only after visual control and receiving a signal from the dispatcher or automation, the driver drives the train to a dead end or on the way of departure.
Then the control cabin is changed. The driver moves into the cabin, which has now become the head. He checks the brake system, makes sure of serviceability. coupling (if the train is connected) and receives a route. At this point, the sign “Train to the depot” or “Final” often flashes on the board for passengers so that people do not sit in an empty train.
- 👮 Exit control: Make sure the platform is empty before sending to a dead end.
- 👮 Change of cabin: Transition to the opposite end of the composition and activation of the remote.
- 👮 Systems verification: Brake and communication test with the dispatcher before the new flight.
In some systems, the driver does not need to physically move to another cab. It can simply turn the key or press the “Change direction” button and control will switch to another remote. However, visual inspection of the cabin is still mandatory.
⚠️ If you fall asleep in the carriage and wake up on the final, when the train has already gone to a dead end, do not panic. The driver will definitely notice you when going around or through the security cameras and help you get out.
☑️ Engineer's algorithm on the finite
Technical features of a turnaround in a dead end
A dead end is a maneuver that requires accurate calculation of the braking distance. The metro train has a huge inertial mass. When approaching the stop at the end of the dead end, the speed should be minimal, usually not more than 5 km / h. The stop must be strictly within the limits limit-bar Or a special sign.
If the train stops too early, it may not completely release the needle neck, which will block the movement of other trains. If it is too late, there is a risk of hitting the buffer. Although modern systems ALS ARS (automatic locomotive alarm) force the train to brake when speeding, the human factor and the technical condition of the brakes play a decisive role.
In a dead end, a technical inspection of the chassis is also often carried out. While the composition is standing, the depot duty officer or the inspector can visually assess the condition of the wheel pairs and current collectors. This time is used for a short rest of the driver before the return flight.
Interestingly, in dead ends are often located devices for washing wheel pairs or sandbox, where the supply of sand used to improve the grip of the wheels with the rail during acceleration is replenished. So the dead end is not just a parking lot, but a mini-service center.
The accuracy of stopping at a dead end is measured in centimeters, since the possibility of transferring arrows for the next train depends on this.
Problems and delays in turnover
The reverse station is the “narrow neck” of the entire line. Any fault here paralyzes the movement in both directions. The most frequent problems are associated with the failure of the hand mechanisms or failures in the alarm system. If the arrow does not get in the right position, the train cannot leave the platform, and the next thread also gets up.
The human factor also plays a role. The delay of the driver when bypassing the car or moving to another cabin for a few seconds can knock down the stroke of movement. During peak hours, when the intervals between trains are 90 seconds, even the slightest delay accumulates, forming a traffic jam in the tunnel.
Backup traffic patterns are used to minimize risks. If the main turnaround path is busy or faulty, the dispatcher may send the train to an adjacent depot or use the backup tracks, if the station scheme allows. However, this always leads to an increase in intervals.
It is important to understand that the noise and vibration that are sometimes felt when turning, often associated with the passage of switches and curves of the path in the neck of the station. This is a normal workflow, indicating a complex mechanical work hidden underground.
- 🛑 Arrow failure: Requires manual transfer or transfer of the train to the backup path.
- 🛑 Communication failure: The driver does not receive the route and must wait for the command.
- 🛑 Passenger factor: Delaying the doors or getting stuck in the passenger slows down the entire cycle.
Why do trains sometimes stand on the final, not leaving to a dead end?
A long parking on the terminal platform usually means that the dead end is occupied by another train that has not yet managed to leave, or there was a delay on the line ahead, and the dispatcher artificially increases the interval. It may also be due to the expectation of a command to transfer arrows if the automation is manual.
Can the train turn around without a driver?
Yes, on lines with a high degree of automation (for example, Moscow City – Neklinskaya in Moscow or some lines in Singapore and Dubai), trains are fully automatic. The system opens the doors, closes them, translates the arrows and changes the control cabin.
What happens if the train doesn't reach the stop in a dead end?
If the train stops earlier, it may not fully clear the pointer area. In this case, the alarm system will not give a command to transfer the arrows, and the next train will not be able to enter the platform. The driver will have to turn back to get up right.
Why do we need a buffer at the end of the dead end?
Buffer stops are massive metal structures designed to stop the train in case the driver does not brake in time. They extinguish the kinetic energy of the composition, preventing the crash and leaving to the surface or in office spaces.