The tracks are exceptionally well-designed, but there's a few nitpicks I have:
- I spawned on the wall of your tripwire area instead of on the tripwires themselves; instead of using tripwires to spawn the player into the map, you should instead use the stat.leaveGame objective (contrary its name, it actually adds 1 when a player logs into your world)
- Whilst I noticed no bugs/issues with the mechanics in the map, the redstone is very inefficient and looks rather old-school, which could negatively impact performance (although I had no problems)
- There is nothing to warn the player that they're going the wrong way, nor anything to put the player back on the track if they go off-course - I'd recommend using execute detect to damage a player that's off-course
- The enderpearl item kinda sucks due to the damage received from using it (come to think of it, I'm not sure I like the fact that you can take damage in a map about racing...)
- Any items that need to be dropped to use (e.g. mushroom, banana peel, etc.) are a little awkward if you're already holding ctrl to sprint, one possible way around this would be using a fishing rod (retextured to be invisible) in the player's off-hand slot, then checking for the item the player has selected in their main hand as they right-click with their off-hand (where the rod is) in order to activate the item
Keep in mind though that I'm really reaching to say anything negative here, as this map is honestly superb. It deserves more attention.