This section describes the four door passenger geometries commonly used in North American transit buses.

• Swing Door
• Bi-fold Door (Infold and Outfold)
• Slide - Glide Door
• Parallelogram Plug Door

For each geometry, a schematic pictorial illustrates the motion, closed, and open positions of the door panels relative to the door opening. This pictorial is supplemented with a text description of the door motion. In addition, the common applications of the particular geometry are listed, significant considerations regarding the geometry are summarized, and implications of the geometry on door panel design and construction are noted.

Description of Geometry
The door panel is mounted to the vehicle by means of a short vertical shaft attached to the top trailing edge of the panel and a pivot arrangement affixed to the bottom trailing edge. When the top shaft is rotated by the actuation mechanism, the door panel rotates about an axis through its trailing edge, to a point where the panel is perpendicular to the side of the vehicle. In the open position, most of the door panel protrudes from the side of the vehicle.

Applications
• Exit doors on transit buses where it is desired to limit passenger access to the vehicle (for fare collection or other considerations) or where passenger actuation of the door is desired.
• Compatible with air-open or push-open spring close actuators.
• Most common door geometry on utility vehicles.

Application Considerations
• Simplest mechanism when utilizing a pneumatic differential engine.
• Doors may be recessed or mounted flush with the vehicle exterior.
• In the open position, most of door panel protrudes from side of vehicle.
• Less suitable for wide openings because of door protrusion.
• Air-open spring close and push-open spring close mechanisms provide a latching capability when door is closed.
Implications for Panel Design
• Door panels must be rectangular and flat .

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Description of Geometry
Each door leaf assembly consists of two panels fastened together with a hinge or hinges. The leading edge is affixed to a guide device that is constrained by a fixed track or rod mounted to the door header. The trailing edge is affixed to a vertical shaft that is connected to the prime mover. When the prime mover rotates the shaft, the hinged panels will move either into the vehicle ("inward bi-fold") or away from the vehicle ("outward bi-fold"). As the two door panels rotate, the leading edge of the assembly is drawn away from the center of the door opening towards the door jamb, opening the door. Typically, two bi-fold door leaf assemblies are used in a door portal, one each opening to the right and left sides, respectively, of the door portal.

Applications
* Entrance and exit doors on standard transit buses

Application Considerations
• Useful for wide openings
• Inward bi-fold doors have minimal exterior protrusion in open position and less intrusion into interior than slide-glide doors of the same portal width.
• Inward bi-fold doors may present a hazard in emergency situations.
• Outward bi-fold doors protrude beyond the vehicle body.
• Bi-fold panels and frames limit the amount of window area.

Door Panel Implications
• Bi-fold doors must be rectangular and flat.
• Bi-fold door panels must incorporate attachment points for hinges and hinge line seals.

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Description of Geometry
Each door panel has a guide device affixed near its leading edge. This device is constrained by a fixed track or rod mounted to the door header. A vertical door shaft is connected to the top and bottom of the door panel near its trailing edge by means of arms and rod end bearings or hinges. When the prime mover rotates the door shaft, the trailing edge of the door is pulled into the vehicle, while the guide device constrains the leading edge to travel towards the door jamb to the "open" position. In the "open" position, the door panel is perpendicular to the side of the vehicle and as close as possible to the jamb. The leading edge of the door panel may protrude beyond the vehicle side in the "open" position.

Applications
• Entrance and exit doors on standard transit buses.

Application Considerations
• Limited protrusion beyond the exterior of the vehicle.
• Wide doors installed on conventional high floor buses may require that the sides of midstep be cut back to provide clearance for the door in open position.
• Doors may be curved to match exterior contour of bus. However, curved doors reduce the clear-opening between door panels in the open position.
• Can be weather tight.
• Not subject to panel lift-out at higher vehicle speeds.

Implications for Door Panel Design
• Attachment points must be provided for door shaft arms.
• Weather seals for lower shaft arm or hinge must be carefully designed

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Description of Geometry
Each door panel is suspended near its top and bottom by curved (boomerang) arms attached to a rotating door shaft mounted inside the vehicle body. A third guide arm is attached to a point near the leading edge of the door and to a point on the vehicle body. When the door shaft is rotated, the door panel moves out of the opening and follows a circular trajectory to a point adjacent to the vehicle body and clear of the door opening. Parallelogram Plug Doors may be used in either single panel or bi-parting configurations.

Applications
• Principal uses are on intercity and tour coaches.
• Vehicles where a flush door and/or no protrusion into body is desired.
• Shuttle vehicles where smooth sides are desired.

Application Considerations
• Door panels may be flat or curved to match vehicle body contour.
• In open position, entire door panel is on exterior of vehicle.
• Door linkages must be designed to withstand forces associated with cantilevered door panel mass.
• Leading edge of door panel overlaps door opening when in fully open position.
• Latching devices may be required to prevent door panel "lift-out" caused by aerodynamic effects at higher speeds.

Implications for Door Panel Design
• Attachment points must be provided for boomerang arms and guide arm.

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