Short Overview on Five Different Kinds of Doors

Currently, due to the changing living styles, and also the advancement in technology, there have been numerous changes in the transport buses, and changes in doors have been one of them. Bus doors have been one of the highly evolving section in this sector, where power operated doors are fitted to ensure the passengers’ comfort and more efficient satisfaction of their needs. There are a number of door types which currently are fitted in the busses, depending on the requirements. In this paper, there will be given a short overview on five different kinds of doors, their operation and comparison of their advantages and disadvantages.

Twin Glider Door

Twin glider door applies a system of interconnected shafts, and it usually contains two leaves, which usually curved inward on the opposite directions leaving a clear passenger path, and on closing the shafts, turning the leaves together and the door locking. These leaves are carried on the steel shafts that are located at the bottom by the bearings which are bolted to the step and suspended from an overhead mechanism.

This kind of doors is usually controlled by an electric system or a pneumatic system, depending on the requirements. The doors can be automated or operated manually. Currently, most of these doors are automated, where the driver uses a closing and opening switch to automatically operate the door. A step is fitted within the door, and one corner of the door panel, which is lower, is cut away in order to clear the step while the door is opening, and the subsidiary panel of the size closing the door panel is carried by the lower swing link which supports the door panel in order to close the cut away portion, when the door is closed. This kind of door is mostly used for the entrances and exits.

Advantages of twin glider doors:

The twin leaves offer a wide area for passenger path.
They have a longer closing and opening time.

Disadvantages of twin glider doors:

They have a wide range of functional temperatures.
Its folding movement is not so suitable, in case the bus is crowded.

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Folding Doors

This is a pneumatic pressure door, which uses the pneumatic power to operate itself. They operate by folding parts together, using a system of interconnected shafts and gear. The folding doors are designed in order to provide an easy and quick space division with a pleasing visual appearance and moderate sound attenuation. They also provide quick sound and sight division with the pull-and-latch simple operation. Folding doors include a number of operators, such as MB-D3 Electrical Bi-fold Operator, although, they can be operated manually or automatically, depending on the requirements.

Folding doors usually have properties, such as a specific operating voltage, overdriven protection and also a maximum operating force. In case of the above examples, it is 300 N. They also have an emergency release handle and a specific opening time. They operate at a specific range of temperature, and the opening speed depends on the temperature.

Advantages of folding doors:

Some types of folding doors can be used in extreme temperatures (-40 to 50 degrees).
It is durable.
Its structure makes it easy to apply in any kind of buses.

Disadvantages of folding doors:

Have a fast opening and closing time (most have 2.5 seconds).
It’s simple and compact in its structure, making it easy to maintain.
Opening speed is affected by the temperature.
Not so suitable in crowded buses.

Glider Doors

This is a type of doors, which when opened the leaves glide, is turning to the inside and the other way round to close. Its mechanism is quite similar to that of twin glider door, apart from the fact that this type has a single leaf. It combines rotary and linear movements to slide the door wings to the side of the doorway as they open. This makes them ideal for both entrance and exit doors, and they are the most popular door type in the market.

Glider doors are usually fitted with pneumatic or electrical driver, where there is a variant to suit all the applications. They have a rapid smooth operation, and the door way is flat or moderately contoured. The aluminum framed door wings are bonded together using a unique fixing system with levers, such that when opened, they turn to the inside giving a clear pathway. It is mostly used for the entrance and exits.

Advantages of glider doors:

Glider doors have a large glass area, offering a maximum sideways vision for the driver.
Some, in order to enable the door to pass over the first step, have a step cut-out.
They have emergency egress by exhausting air.

Disadvantages of glider doors:

Simple gliding doors, the setback of approximately 70 mm from exterior are less vulnerable to damage.
They offer a clear passage path.
They take more closing time than the folded type.

Sliding Plug Door Sliding plug door mechanism can either be pneumatic or electrical type, depending on the requirements. The mechanism includes a lever element arranged to move with a door panel, the lever element with an actuator of the mechanism. In case of the pneumatic type, the doors open by means of the plugging out of portal followed by the sliding movement within the car body. The plugging is realized by the rotation of the door pillars which push out the telescope on which the door leaves are mounted.

The rugged construction and simple design of the mechanism provides the maximum reliability, when the shelf plate shallow depth allows the sliding plug door to be fitted in places, where other kinds of doors cannot be fitted. Other features include the option of having the hidden pillar tubes located in the body cavity at the side of the door aperture. In such configuration, the pillar tubes are invisible from the outside or inside vehicle.  It improves the vehicle’s aesthetics and also protects pillar tubes from the damage. The modern design allows the double wing door to be fitted in the vehicle aperture of 1350 mm in order to open sufficiently and to leave to the clear opening in the excess of 1200 mm and protect it from damage. Although, the doors can be viewed as the single and double wing versions; such doors ideally suit for fitting at both exit and entrance doors.

Advantages of sliding plug door:

Occupies less space, hence, efficient in crowded buses.
The door slide in the body, hence, prevents passengers from the accidentally knocking on the door.
Its drive mechanism provides the maximum reliability and efficiency, hence, one of the best models in the market.

Disadvantages of sliding plug door:

The pillar tube gets protection from the cavities, hence, the higher protection.
In case of the break down, more work can be required due to the fitting in, as compared to the folding type.

Swing Plug Door

The Swing Plug door can be defined, based on the aspect that the door opens by the means of plugging out of the door portal, followed by a swing movement until it is in the open position. They consist of a door mechanism, door wings, rotating rods, of an emergency control and also control equipment. The door wings are all-glued, of a sandwich construction, consisting of Al-profiles, covering Al-plates and filler. Door is glazed with single safety glass. The door wings can be locked in the closed position, and there are outer buttons installed for controlling the door.

The upper mechanism secures opening and closing of the door, while an electromotor with a gearbox is used as a driving constituent. The movements are generated by the rotation of the door pillars which are connected with the door leaves by the means of the pillar arms. The door mechanism drives both the door wings simultaneously by the means of draw bars. During the movement, the door leaves are kept parallel to the car body and with the parallel arms. The draw bars are the one which transfer the forces on the rotating rods holding the door wings. The doors have locks installed in the door wings, and the door is usually locked by triangular or square key.

Advantages of swing plug doors:

The door cylinder is kept in a way to realize the mechanical lock, hence, safety maintained in case it losses the air pressure.
If electric power is lost, the emergency release enables the manual opening of the doors.
The compact package minimizes the intrusion in the passengers’ space.

Disadvantages of swing plug doors:

The electric operation eliminates the inconvenience of air piping and the weight and cost of an air compressor.
They have a short closing time, hence, are more efficient.
Requires higher amount of current.
In less spacious bus stops, the movement of the door can be quite ineffective, as compared to other models.

Reason for Selection of the Folding Doors and the Sliding Doors as the Best Door Designs

The length of time a bus is packed at a station is very important, especially during the short headways and service peak periods. Some passenger behaviors, such as the deliberate holding open of doors, has a detrimental effect on maintaining the short dwell times and service timetable. Mechanical malfunction can be resulted, because the door holding is also a significant contributor to buses having to be removed from the service. The use of sliding doors and folding doors reduces this risk, since it’s quite hard to hold them when set in the closing motion.

Sliding door tends to maximize the width of the door aperture, meaning that one can easily achieve a double flow in and out of the bus, as compared to other models.

When it comes to safety, the doors are safe, especially where no conductor is involved. The opening movement of the two kinds of doors are in way that it’s not easy for a passenger to get injured during the opening and closing, unless on extreme occasions.

Sliding doors that retract within the body of the bus wall do not intrude into the passenger’s space, except when crossing the threshold of the vestibule. Their action and design are relatively simple mechanically and quick, since they have only a backward and forward direction of the movement.

In case of the folding doors, they can be easily operated manually, in case of any technical problem, hence, safety increased.


Different kinds of doors have different features and different modes of operation, and each type fits in a specific situation, depending on the conditions in which they will be operating in. It is always necessary to analyze the door requirements, which will suit the bus before choosing the door type. This will avoid malfunctioning or inefficiency in the future.

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