By the way, a few minutes ago a discussion with Boot2490 about calculator racing games and particularly Lotus Turbo Challenge eventually led to me bringing up an old project of mine that I have never completed that was meant to be an xLIB clone of Lotus Turbo Challenge, to show that such racing game with basic hills and race track could be done in TI-BASIC and libraries. He asked me how that game was made, but it's rather hard to explain without pictures, because most of the secrets are inside the sprite sheets. If you look at the game sprite sheet attached to this post, it should tell you enough about how the racing track was done. This is quite a necropost here, but I thought I would share now that this was brought up on IRC, for anyone curious, and maybe this could be useful for anyone who would like to make a similar project in the future.
The game engine, from what I remember, also had support for multiple kind of track textures, but in BASIC it would have required hacked pics, meaning hassle to send the files to a calc.