Good train door design needs a good interface between the car body and the door. This means the doors remain sealed against draughts, water and noise.
Door guides and supports needed to be mounted within the section of doorway which is protected by the door seals and other suitable means – ensuring that no ingress of dust, debris, or any other foreign matter is likely to wear or damage the door equipment.
The proposed design – which needed approval early in the process – needed to be maintenance friendly and suited to an annual cleaning regime.