A transit bus door panel should be durable, readily maintained and repaired, and free of inherent hazards to passengers. There are several approaches to the design and construction of a satisfactory door panel, so door panel specifications should be performance oriented rather than design specific. This section outlines key design requirements for transit bus door panels, some of which were previously incorporated into the "White Book" (3) and other specifications. Selected features are illustrated in Figures 4-1 and 4-2.

Design Life
Door panels shall be designed to function properly for 12 years from vehicle date of service under the climatic and atmospheric conditions prevalent in the vehicle operatin area.

Design Features
• Glazing area shall be maximized consistent with maintaining the deflection character istics define under mechanical properties.
• The edge of a 6 inch high curb shall be visible to the seated driver through the closed front door when the bus is more than 12 inches from the curb.

Materials
• Door panel structural frames and skins shall be made of corrosion resistant metals or non-metallic materials. It is recommended that carbon and LAHT steels not be used for door panels due to their susceptibility to corrosion.

Glazing
• Door window glazing shall conform to the requirements for side window glazing.
• Door window glazing rubber will permit the installation and removal of the window glazing material without disassembly of the door panels.

Construction
• Metallic door panel frames shall be assembled utilizing mechanical fasteners or electric welding.
• Frame members and/or reinforced fastener attachment points shall be provided for attaching door linkages, grab handles, touchbars and other linkage and ancillary items.
• A kickplate fabricated from a corrosion resistant metal shall be provided on the lower portion of any exit door panel having glazing only in the upper portion of the panel

Structural Requirements
• Elastic deflection of the door panel (with glazing installed) shall be no more than 0.25 inches when a 200 pound load is applied to an area of 10 square inches at the center line of the door while the top and button of the door panel are supported by line supports located 2 inches inward from the inmost top and bottom edges of the door panel.

Exterior Finish
• The visible exterior surface of the door panel shall be finished using the same finish applied to the exterior surface of the vehicle.

Maintainability
• It shall be possible to repair damage to the door panel, other than "racking" or distortion of the door frame, using conventional automotive body repair techniques.
• It shall be possible to replace door window glazing without disassembly of the door panel.
• It shall be possible to replace leading edge seals without disassembly of the door panel.

Protection
• When the doors are fully closed, the hard surfaces of the leading edges of the door panels shall be at least 4 inches apart.