1. What Happens If a Train Stops in the Wrong Place at Platform Screen Doors?
If a train stops slightly too early or too late at a station with platform screen doors, the train doors and the platform doors will not line up. As a result, passengers cannot get on or off [1]. To prevent this, stations use a device called the Automatic Train Stop Control (TASC). This system places small devices called "ground transponders" at several points before the station. These send distance information to the train [1].
The train’s computer compares its current position with the correct stopping point. It then creates a braking plan to decide how hard to apply the brakes. The train follows this plan to stop precisely [1]. This is somewhat like a cyclist gently squeezing the brakes before a white line. However, for a train, a machine measures the distance and makes the plan. Even with this system, it is said that occasionally the train may need to stop and restart to align correctly [1]. Once the train stops, the doors do not open immediately. Who gives the signal to open the platform doors and train doors at the same time?
2. How the Conductor Switch Links Train Doors and Platform Doors
On conventional lines, after the train stops, the conductor checks that the stopping position is correct. Then, the conductor operates the "conductor switch" to open the train doors. The platform screen doors open in sync with this action [2].
At stations where JR East has installed platform doors, there are sometimes signs hanging from the ceiling that show the connection status. There are three types: "Link," "Rush," and "Separate." Normally, the setting is "Link," where both opening and closing are synchronized with the conductor’s switch. In "Rush" mode, the doors open in sync, but station staff operate the closing separately. In "Separate" mode, there is no synchronization [2]. On conventional lines, these three modes are used. But what about the Shinkansen?
3. Why Shinkansen Platform Doors Are Not Connected to the Train
The method for Shinkansen platform doors (movable barriers) differs by line. A 2023 explanation states that for the lines and sections covered, there is no function to link with the train vehicles. The plan for Tokyo Station mentioned later is from a different time period [2].
On the Tokaido Shinkansen, station staff open the movable barriers first. The conductor then sees this and opens the train doors. This order is the reverse of conventional lines. At unmanned stations and similar locations on the Kyushu Shinkansen, the conductor uses a remote control to open and close the barriers [2]. This description is from 2023 and may not be the same today. However, it shows that in systems without automatic links, human eyes and voices ensure safety. To link the doors, the system needs to know "which vehicle’s doors are where." But even trains running on the same tracks have different numbers and positions of doors. How is this challenge overcome?
4. How One Platform Door Works for Trains with Different Door Positions
Trains running on the same track can have different door numbers and positions. This includes commuter trains, limited express trains, and trains from other companies. Aligning the platform door openings with all vehicle types is a major challenge for installation [3].
Keikyu Corporation solved part of this problem by making the doors themselves wider. Their "Anywhere Door" has an opening width of about 3.2 to 3.6 meters. This is wider than the typical 2 meters. Calculated, it is about 1.6 to 1.8 times wider [3]. It is said that the system can accept a deviation of plus or minus 850 millimeters. This means passengers may be able to board or alight even if the train is 85 centimeters too far forward or backward [3]. This door automatically detects the number and arrangement of train doors, so no device is needed on the train side. A demonstration experiment was reported to be held at Miura Kaigan Station in October 2016 [3]. While wider openings help, they do not solve every case where door numbers differ. Is there a way to identify them more precisely?
5. How QR Codes on the Toei Asakusa Line Show Door Numbers and Positions
On the Toei Asakusa Line in Tokyo, QR code labels are attached to the train doors. Scanners mounted above the platform detect the state of the train doors from the movement of these QR codes. This controls the opening and closing of the platform doors. The Tokyo Metropolitan Bureau of Transportation and Denso Wave developed this jointly. It is said to be the first use in a subway system, adopted in 2019 [4].
Before adoption, a verification test of the synchronization was conducted at Daimon Station for about one month in November 2017 [4]. The QR codes contain information about the number of cars in the train and the number of doors [4]. It is important to note that QR codes are not a technology to stop the train. They are a technology to identify the number and position of doors. Aligning the stopping position is the job of a separate device, like the TASC mentioned in section 1. Separating the roles of "identifying" and "stopping" makes the system clearer [4].
For Tokyo Station, a separate plan has been announced. JR East announced that platform screen doors at Tokyo Station will use QR codes to automatically recognize door positions. Only the relevant sections will open automatically. Operations are scheduled to begin by the end of fiscal year 2028 for tracks 20 and 21, and by the end of fiscal year 2029 for tracks 22 and 23. This is said to be the first use in the world for Shinkansen. Currently, station staff open and close them. Automating the closing process is a topic for future study [5]. Methods tested in subways are planned to be used for Shinkansen. Stations where humans opened doors first will now use QR codes to identify door positions.
6. Measuring the 2 m and 3.4 m Door Widths at Home
Let us feel the width of platform doors with our own bodies. On a hallway or room floor at home, use a measuring tape or string to measure 2 meters and mark the ends. Then, measure 3.4 meters from the same spot. 2 meters is the typical width of a platform door. 3.4 meters is the middle width of Keikyu’s "Anywhere Door" (3.2 to 3.6 meters) [3].
The difference is 1.4 meters. You can imagine how much room this allows for a train that is 85 centimeters off position. Dividing 3.4 meters by 2 meters gives about 1.7 times. You can calculate this yourself to check. When you go out, try observing a train stopping at a station with platform screen doors. Stand in a safe place on the platform, away from the yellow line. Do not lean against the platform doors. If there are signs hanging from the ceiling, look for which of "Link," "Rush," or "Separate" is displayed [2]. If you want to read more, explanations of the opening and closing differences for Shinkansen [2] and the announcement article for Tokyo Station’s Shinkansen platform doors [5] are available in Japanese.