I stood at the wrong door! Why do subway doors always change the direction they open?

Audit expert: Hu Qizhou, Associate Professor, School of Automation, Nanjing University of Science and Technology

Have you ever had the experience of trying to cross the subway car to get off during rush hour? The doors were open on the left at the previous station, but suddenly they were opened on the right at the next station! As a result, you finally squeezed to the door, but you had to squeeze back. Not only was it uncomfortable, but you also received cold stares from other people in the car. It was really embarrassing.

As an experienced subway user, I have always been confused about the direction of subway door opening. Why do I get on the subway from one side and get off from the other side at the next stop? Does the driver randomly choose one side to open the door or does he have a set of systematic rules?

Different subway stations

As one of the most convenient means of transportation in modern society, the subway is very popular among office workers. To discuss the reasons, we have to say that there are many accidents on the way to work. Wind and rain are common, and there are occasional sandstorms. Of course, there are also the most terrible traffic jams. In this case, the subway stands out from many means of transportation with its advantages of punctuality, efficiency and speed, and escorts workers to work.

In fact, to answer the question of where the subway doors open, we have to start with the platform layout of the subway .

Subway platform types can be roughly divided into island type, side type and mixed type . According to the needs of passenger flow management, there are some other types of stations, but they are basically developed from these three types of structures.

The island platform is the most common type of train platform, with tracks on both sides and a platform in the middle. There are boarding passages on both sides of the island platform, so passengers do not need to change platforms to get on the train. Even if they accidentally get on the wrong train, it is very convenient to return, as they just need to get off at the next stop and take the train in the opposite direction.

Island platform at Clapham Common station on the London Underground

Source: Wikipedia/Diliff

It can be said that the island platform is convenient for centralized management and for passengers to turn around midway, but the construction cost is high and it is difficult to expand the waiting room later. When my friends came to Beijing Science Center to visit the exhibition, they got off at Anhuaqiao Station on Beijing Metro Line 8, which is an island platform.

A side platform is also called an opposite platform. It has a structure where the track is in the middle and the platforms are located on the left and right sides. It is also a common platform type. Generally speaking, a side platform is defined as a station with tracks on only one side. Some smaller stations only have one platform and one track, which also belongs to a side platform.

Side platform of Haidian Huangzhuang Station on Beijing Subway Line 10

Source: Wikipedia/Yiyuan New Residence

The side platform has a simple structure and low construction cost. It is also easy to expand the platform after it is built. However, it is inconvenient to manage and it is troublesome for passengers to turn around. If passengers find that they are standing on the wrong platform, they often cannot cross the track directly, but need to take a detour through an underground passage or overpass to reach the opposite platform.

A mixed platform means that there are both an island platform and a side platform at one station. It has the characteristics of both platforms and is also the most expensive. The mixed structure of island and side platforms includes: double island platform, Spanish platform and stacked platform.

The double island platform at the National Library Station of Beijing Subway

Source: Wikipedia/N509FZ

As it has the advantages of both island platforms and side platforms, hybrid platforms can greatly improve train operation efficiency, reduce operating costs, reduce energy consumption, improve passenger safety, and reduce passenger congestion. However, its disadvantages are also obvious: the construction cost of hybrid platforms is high, and the maintenance and management costs are also relatively high. It requires appropriate personnel to manage it, and improper management will bring safety hazards. Therefore, hybrid platforms are often found in subway stations with busy traffic in economically developed cities.

The old platform of Changchun Station on Changchun Light Rail Line 3, which adopts the Spanish-style platform

Source: Wikipedia/TowerCard

After understanding the subway platform form, it is not difficult to conclude that the opening direction of the train door actually depends on the structural form of the subway platform. When the platform forms of the two stations before and after are different, the opening and closing direction of the door may change.

Of course, depending on the actual situation, in real life there are also situations where the doors are opened from the same side at most stations along the entire journey, or where the doors are opened almost entirely alternately from left to right.

Which side do subway doors open?

However, how can we accurately determine the direction in which the car door opens?

The easiest way: check the prompts on the subway door display screen.

In fact, the door opening direction problem can be solved by paying a little attention when riding the subway: first, if the subway has a dynamic electronic display screen, you can pay attention to the prompts on the screen and follow the instructions to understand the door opening direction; the second most common reminder is the voice prompt. When the door is opened, the corresponding prompt light above the door will light up or flash. Please be sure to check before arriving at the station.

Dynamic display screen of Beijing Subway Line 8

Source丨Editor

There is one more small issue I want to remind everyone. If your clothes or schoolbags are caught by the door when getting on or off the train, don't panic. You can try to pull them gently. Generally, the corners of your clothes can be pulled out normally. If they are really stuck, you can wait until the next station arrives and the door automatically opens. If you are really in an awkward situation where all the subsequent stations open the opposite door, you can contact the security guard patrolling in the carriage to handle it , or contact the staff for help through the emergency call device in the carriage .

There are two types of buttons installed on both sides of the doors in the subway car, namely the yellow "emergency call device" button and the red "emergency unlocking device" button .

It is important to note that you should not pull the emergency unlocking device at will because of extreme panic . Under the protection of the vehicle system, once the emergency unlocking device of the train is triggered, it will cause the train to brake automatically, and must be manually restored by a dedicated person before it can operate normally. Therefore, if you touch it at will unless there are special circumstances, it will delay the normal operation of the train and hinder the normal travel of all passengers on the entire line. If you use it in non-emergency situations, you will bear the corresponding legal responsibilities according to law.

In the subway, the platform is a very important part. Without the platform, you can't get on or off the train, let alone take the subway. Therefore, in order to save your time and get to work on time, we need to check the route in advance and take a good look at the transfer route, so as not to waste time due to inconvenient transfers or taking the wrong train.