I made a cake several weeks ago for a cousins adorable 2 year old, who is VERY into cars. I'd seen some race track cakes, but most of them were carved. Meaning, they stacked cakes, then carved away a portion of them and frosted over that. I wanted to avoid the carving, because 1. I hate to throw cake away, and 2. it can be difficult and messy. Plus, it's hard to frost over carved cake, as there are a lot more crumbs.Instead of carving, I opted to use rice krispy treat to sculpt the track. You can see how it was done in the photos below.
Once the basic structure is complete, you can finish decorating with buttercream frosting and fondant accents. Here, the only fondant decorations are the little race cars.