Slot car track is not wide enough. Borders are necessary and often named: aprons, curbs, kerbs, shoulders and speed corners.

For decades flat borders have been made with foam, cork, poster board, etc. However banked turns were messy until now.

This part comes out perfect with SLS printing in Nylon 12. However this part also shows the limitations of FDM printing. We do get one good surface with FDM so the part is placed to keep the racing surface smooth and everything else needs clean up.

The clips which make the attachment, will break with PLA, use PETG or use another attachment method.

I also uploaded the simple shape that is easier to print. It will not work with guardrails and can be attached with silicon if the tabs and clips come off with the support. https://makerworld.com/en/models/1970758-12-banked-slot-car-track-border-solid-print#profileId-2118920