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As Andy has said they can be supported. If your layout is permanent then plywood support for the track and borders. Lay the track and boarders on ply and trace the raised track. Cut out with jigsaw and make supports. 

I agree but there are a few things you can do. The elevated cross over has pylons that can be turned to hold the borders: https://uk.scalextric.com/products/elevated-cross-over-c8295 It is not very clear on this pictures but there are thin "fingers" that stick out that are there to hold the barriers and borders. The track supports can be used as well: https://uk.scalextric.com/products/track-supports-and-clips-c8226 In addition to the block tops there are also grey ones that pinch the edge of the border or track as well. All easily found online... There are also other tricks like using duct tape or "blue tak" to hold it or if you want something permanent you can use plaster of paris , wood, nails and screws to hold it all in place...  

How about making borders/shoulders that don't fall off when they are raised up when a layout has an incline or overpass?

You do realise that you are replying to yourself? (the identical numbers after your name show you’re the same person & your posting history removes any possible doubt!) 😉

Ian, same name, same thoughts! I was thinking of using the red Land Rover as a basis for the blue Goodwood recovery vehicle and looking at my E-Types to convert to the safety car. It would be fantastic if Scalextric could make these as I don't really like the idea of chopping a near £50.00 model up! While they're at it a Jaguar XKSS and C-Type would be great to go along with the D-Type... you can only hope lol!